State of California
California Natural Resources Agency
Department of Water Resources
State Water Project
Long-Term Drought Plan
March 2024
This report was prepared by:
California Department of Water Resources
Andrew Schwarz
State Water Project, Climate Action Manager
Molly White
State Water Project Water, Operations Manager
John Leahigh
State Water Project, Assistant Division Manager for Water Management
Rylan Gervase
State Water Project, Deputy Director Policy Advisor
John Yarbrough
State Water Project, Assistant Deputy Director
Anthony Navasero
Drought Coordinator
With Contributions from:
Tracy Hinojosa
State Water Project Water Operations Compliance Coordination, Manager
James (Tripp) Mizell
Office of General Council
Jacob McQuirk
State Water Project Water Initiatives Planning and Management Branch,
Manager
Rosemary Hartman
State Water Project Ecosystem Monitoring, Research, and Reporting,
Environmental Program Manager
Jesse Dillon
State Water Project California Aqueduct Subsidence Program, Manager
Dustin Jones
State Water Project Water Operations Branch, Supervising Engineer
David Rennie
State Water Project Asset Management, Manager
Contents
California Department of Water Resources i
Contents
Chapter 1. Introduction Page 1-1
1.1 SWP Water Supply Planning Objectives Page 1-3
Chapter 2. California Climate, Variability, and
Historical Droughts and Impacts Page 2-1
2.1 California Climate and Variability Page 2-1
2.2 Historical California Droughts Page 2-2
2.3 Uniqueness of California Droughts Page 2-6
Chapter 3. Analysis of Potential Future Droughts Page 3-1
Chapter 4. SWP Water Supply Allocation
Planning and Operations Page 4-1
4.1 SWP Annual Allocation Planning Page 4-1
4.1.1 Water Supply (Runoff) Forecasts Page 4-1
4.1.2 SWP Water Supply Allocation Process Page 4-2
4.2 Real-Time Operations Page 4-3
4.3 Additional Allocation and Real-Time Operations Considerations Page 4-5
4.3.1 Central Valley Project Operations and Coordinated Operations Agreement Page 4-5
4.3.2 Feather River Requirements Page 4-6
4.3.3 SWP Storage Targets Page 4-7
4.3.4 State Water Contractor Delivery Requests Page 4-8
4.4 Regular Communications and Coordination Activities Page 4-8
4.4.1 Water Operations Management Team Page 4-8
4.4.2 CALFED Operations Group Page 4-9
4.4.3 State Water Contractors Water Operations Committee Meetings Page 4-9
4.5 Drought Planning Activities Page 4-9
4.5.1 Annual SWP Drought Contingency Planning Page 4-10
4.5.2 Drought Toolkit Page 4-10
4.6 SWP Operational Drought Actions Page 4-11
4.6.1 Human Health and Safety Water Supply Allocation Page 4-12
4.6.2 One Facility Operation Page 4-12
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ii California Department of Water Resources
4.6.3 Facilitation of Transfers and Exchanges Page 4-12
4.6.4 Water Transfer Delay Programs Page 4-13
4.6.5 Environmental Actions Page 4-13
4.7 Statewide Drought Actions Supported by the SWP Page 4-14
4.7.1 West False River Drought Salinity Barrier Page 4-14
4.7.2 Temporary Urgency Change Petition Page 4-15
4.7.3 State Water Contractor Conservation Actions Page 4-15
4.7.4 Review of State Curtailment and Transfer Policies Page 4-16
4.8 Limits and Tradeoffs of Extreme Drought Page 4-16
Chapter 5. Lessons Learned from the 2020–2022
Drought Emergency Page 5-1
5.1 Communication Page 5-1
5.2 Temporary Urgency Change Petitions Page 5-1
5.3 Delta Barriers Page 5-2
5.4 Aqueduct Reverse Flow Operations Page 5-2
Chapter 6. SWP Actions to Improve Long-Term Drought
Resilience and Add Flexibility, Efficiency, and Capacity Page 6-1
6.1 Delta Conveyance Page 6-1
6.2 California Aqueduct Subsidence Program Page 6-2
6.3 Forecast-Informed Reservoir Operations Page 6-2
6.4 Storage Investigations Page 6-3
6.5 Evaluation and Adjustment of Oroville Carryover Storage Targets Page 6-4
6.6 SWP Enhanced Asset Management Page 6-4
6.7 DWR Climate Action Plan Page 6-4
6.8 SWP Climate Change Resilience Planning Page 6-5
6.9 Climate Change and Drought Risk Communication Page 6-5
Chapter 7. Actions to Improve Long-Term Drought
Resilience that SWP Supports and Contributes Toward Page 7-1
7.1 West False River Drought Salinity Barriers Programmatic Approach Page 7-1
7.2 Improved Seasonal Forecasting Page 7-2
7.3 Continuing Commitments to Environmental Resiliency Page 7-3
Contents
iii California Department of Water Resources
7.4 North Delta Barriers Page 7-5
Chapter 8. References Page 8-1
Chapter 9. Useful Web Links Page 9-1
Figures
Figure 3-1 Declining Delta Exports with Climate Change
during Five-Year Drought Page 3-3
Figure 4-1 Historical SWP Table A Water Amounts requested by
Water Contractors and Approved for Delivery, 1968–2023 Page 4-3
Figure 4-2 SWP Allocation Process and Forecasted Operations Page 4-5
Tables
Table 1 Estimated Average and Dry-Period Deliveries of SWP
Table A Water (2043 Climate Change Conditions without
Adaptation, in TAF/year) and Percent Reduction in SWP
Table A Amount From the Same Drought With Current
Climate Conditions 3-4
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iv California Department of Water Resources
Acronyms and Abbreviations
AR atmospheric river
B120 Bulletin 120
CASP California Aqueduct Subsidence Program
CDFW California Department of Fish and Wildlife
CVP Central Valley Project
CW3E Center for Western Weather and Water Extremes
DCR Delivery Capacity Report
Delta Sacramento-San Joaquin Delta
DFM Division of Flood Management
DRA drought relief action
DRY Drought Relief Year
DWR California Department of Water Resources
D-1641 Water Rights Decision 1641
ESA Endangered Species Act
FIRO forecast-informed reservoir operations
HAB harmful algal bloom
HHS human health and safety
ITP incidental take permit
LTO long-term operation
maf million acre-feet
NMFS National Marine Fisheries Service
Reclamation U.S. Bureau of Reclamation
RVOS River Valve Outlet System
State Water Board California State Water Resources Control Board
Contents
v California Department of Water Resources
SWC state water contractor
SWP State Water Project
taf thousand acre-feet
TUCP temporary urgency change petition
USACE U.S. Army Corps of Engineers
USFWS U.S. Fish and Wildlife Service
WFR drought barrier West False River drought salinity barrier
WOMT Water Operations Management Team
1983 Agreement “Agreement Concerning the Operation of the Oroville
Division of the State Water Project for Management
of Fish and Wildlife” between the California
Department of Fish and Wildlife and the California
Department for Water Resources, August 1983
State Water Project Long-Term Drought Plan
vi California Department of Water Resources
Chapter 1. Introduction
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Chapter 1. Introduction
The 2024 State Water Project (SWP) Long-Term Drought Plan consolidates
information and actions taken during past droughts along with descriptions
of the actions taken by the SWP to plan for and prepare for future droughts.
The scope of the SWP’s drought planning activities is driven by the role the
SWP plays within California’s water management system during times of
drought. The SWP’s planning is specific to its role as a wholesale water
provider. The SWP’s drought planning is necessarily different from the
planning by other water managers that are responsible for directly providing
water to end-use customers. For these water managers, drought planning
generally includes identifying a portfolio of different water supplies and
demand management actions that ensures a minimum amount of water can
be provided with a set degree of certainty. Retail water suppliers have a
“duty to serve” water demand within their service areas and must have
detailed contingency plans for meeting demand during drought conditions.
The SWP, as a wholesale water supplier, makes no guarantee of annual
water deliveries. Instead, the SWP stores and delivers available water to the
maximum extent possible within regulatory, contractual, and operational
constraints. Users of SWP water acknowledge and understand that SWP
water supplies will fluctuate significantly from year to year. Nonetheless, the
SWP is focused on maintaining, to the maximum extent possible, the
reliability and resiliency of SWP water supplies and other benefits in the face
of climate change and other system stressors. In addition, SWP encourages
public water agencies to do their own planning in accordance with state
requirements and Federal Emergency Management Agency and National
Drought Mitigation Center recommendations. Key to supporting those
efforts, the SWP Delivery Capability Report (issued every two years)
provides probabilistic estimates of current and future SWP deliveries to
support risk assessments, impact analysis, and investment planning.
The SWP is a critical backbone water supply and water conveyance system
that provides water to other water agencies — not to individual customers.
The water supplied by the SWP becomes part of the water supply portfolio of
those public water agencies that have contracted to receive SWP water. The
water supply obligations upon the SWP are defined within the contracts
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between DWR and these agencies. This water supply obligation is based on
the concept that the SWP will convey and deliver water — as it is available.
By design, the amount of water that the SWP is obligated to provide varies
with hydrology.
In addition to providing water supply, the SWP has an important role, along
with others, in meeting Sacramento-San Joaquin Delta (Delta) flow and
water quality objectives set by the California State Water Resources Control
Board (State Water Board). The SWP operates its reservoirs and pumping
facilities to meet these objectives, which are a condition of the SWP’s water
rights permits. During a drought, circumstances may arise where,
independent of system operations and management, not enough water is
available to meet all needs. In these circumstances, the SWP is a partner
with the Central Valley Project (CVP), the State Water Board, California
Department of Fish and Wildlife (CDFW) and other resource agencies, to
allocate water to meet the most critical needs given the limited amount of
water and uncertainty about future conditions.
Changing hydrology — including more frequent, longer, and extreme
droughts resulting from climate change — will challenge the SWP and other
water suppliers throughout California. Addressing these climate change
challenges will require planning, investment, and innovation at State,
regional, and local levels. This SWP Long-Term Drought Plan is one part of a
multi-pronged response to these challenges. Additional drought planning and
climate adaptation information is provided in the California Water Plan
Update 2023, SWP Delivery Capability Report (DCR), and DWR’s permits to
operate the SWP. Further analysis and planning will be provided later in
2024 in the SWP Climate Adaption Analysis, Watershed Resiliency Grants,
and San Joaquin Basin Watershed Studies.
The scope of actions taken by the SWP to plan and prepare for future
droughts is intended to maximize the storage, conveyance, and delivery of
available water within physical and regulatory constraints. This SWP Long-
Term Drought Plan describes historical California climate and droughts,
analysis of future climate and drought vulnerability, SWP water supply
planning objectives, SWP water supply allocation planning and operations,
SWP drought planning actions, lessons learned from previous droughts, and
SWP actions to improve long-term drought resilience and enhance the
physical capabilities and flexibility of the system.
Chapter 1. Introduction
California Department of Water Resources 1-3
Consolidating this information into a single document is intended to provide
additional clarity on the scope of SWP drought planning activities as well as
to show how many different activities work together to provide a
comprehensive planning approach for SWP water management.
DWR will review this drought plan every five years, at a minimum, and will
update the plan following significant drought events.
1.1 SWP Water Supply Planning Objectives
The SWP adheres to the following objectives to guide operational decision-
making and development of SWP water supply allocations. These objectives
require considered decision-making to manage trade-offs during critically dry
years:
•
Deliver water supply to meet minimum human health and safety
(HHS) needs.
HHS demand for water is based on minimum unmet water demands to
meet domestic supply, fire protection, and sanitation needs during the
year. The minimum Delta export threshold needed to support annual
HHS demands varies from year to year and by season. Pursuant to the
SWP’s 2022 HHS guidelines, demands are currently based on minimum
water supply and are limited to 55 gallons per capita per day. These
guidelines are expected to be updated because of recent legislation.
•
Preserve upstream storage for future dry year and drought protection.
To prepare for future dry conditions the SWP plans for targeted
carryover storage. (Carryover water is water that could have been
delivered but was held in storage instead; increasing the carryover
storage decreases the supply delivery in the year it was stored but
may increase supply in subsequent years. However, if the subsequent
year is wet, the additional stored water may provide little or no benefit
and may have a cost in terms of flood protection.) This carryover
target was 1.3 million acre-feet (maf) for several years. During the
2012– 2016 drought, it became evident that DWR needed to preserve
additional carryover storage in Lake Oroville to meet contractual and
regulatory requirements should the following water year be dry. In
2018, the Oroville carryover target was evaluated and increased by
300 thousand acre-feet (taf), and beginning in 2019, DWR
implemented an end-of-water year storage target of 1.6 maf.
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•
Meet regulatory requirements.
The State Water Board issued Water Rights Decision 1641 (D-1641) to
DWR and U.S. Bureau of Reclamation (Reclamation) in 1999. D-1641
includes water right permit terms and conditions to implement water
quality objectives to protect municipal and industrial and agricultural
beneficial uses in the Delta as well as water quality and flow objectives
to protect fish and wildlife beneficial uses. The objectives vary by
month and by water year classification. In addition to D-1641
objectives, the SWP also provides for minimum instream flows to the
Feather River as well as additional flows through export reductions in
the south Delta for State and federal Endangered Species Act (ESA)
protections as required by the biological opinions issued by the
National Marine Fisheries Service (NMFS) and U.S. Fish and Wildlife
Service (USFWS) and the incidental take permit issued by the
California Department of Fish and Wildlife (CDFW).
•
Deliver water based on water rights priority.
In addition to providing water to meet minimum HHS and Delta water
quality and flow objectives, other deliveries are made under contract
to entities downstream of Lake Oroville that assert senior water rights.
Upon the construction of the Oroville Reservoir facilities in the 1960s,
DWR entered into agreements with districts that claimed more senior
water rights than the State and that divert water downstream from the
City of Oroville. Pursuant to these agreements, DWR supplies up to
approximately 955 taf of water each year during the contracted
irrigation season (typically March through October). Outside of the
irrigation season, these districts historically have taken delivery of
water for beneficial uses, such as rice stubble decomposition and
waterfowl habitat.
•
Maximize diversion to storage and delivery of water supply.
During winter and spring, when storm events produce natural runoff,
to the extent possible, the SWP maximizes diversion to upstream
storage to be released later for rediversion at the SWP south Delta
export facility or for Delta requirements. In addition to capturing runoff
upstream, the SWP maximizes south Delta exports during the winter
and spring for direct delivery and for storage in San Luis Reservoir for
future delivery to state water contractors (SWCs).
Chapter 2. California Climate, Variability, and Historical Droughts and Impacts
California Department of Water Resources 2-1
Chapter 2. California Climate, Variability,
and Historical Droughts and
Impacts
California has a natural landscape that is diverse from its coastal shores,
deserts, and fertile central valley to its foothills and mountain ranges.
California has a widely variable climate dependent upon the latitude,
elevation, and proximity to the coast and has generally been described as a
Mediterranean climate of warmer, drier weather in the summer and cooler,
wetter weather in the winter. California’s climate is more variable than any
other location in the United States with annual precipitation across the state
varying from a less than 11 inches to almost 43 inches. This variability
seems to be increasing in recent decades, with California experiencing its
second driest year on record in 2021 and its wettest year on record in 2023.
California’s natural variability has historically resulted in periods of extended
dry conditions, often resulting in significant droughts. But not all droughts
are the same, and not all parts of California experience the same dry
conditions. The following summary describes some of the important aspects
of California climate, its variability, and descriptions of significant drought
periods and their impacts. The difficulty in predicting these conditions and
the uniqueness of each past drought provide insights into the challenges of
managing one of California’s most important water resource projects.
2.1 California Climate and Variability
California's hydroclimate presents a complex picture marked by geographical
disparities, climatic extremes, and a critical dependence on precipitation
patterns. The majority of precipitation occurs in the winter months and falls
over the northern half of the state, particularly along the coastal western
region and Sierra Nevada mountains. Throughout California, atmospheric
rivers (ARs) play a pivotal role. These intense concentrated pulses of water
vapor can deliver upwards of 50% of annual rainfall in just a few days.
(Dettinger et al. 2011)
The hydroclimate variability in California is closely connected to the state's
Mediterranean climate, characterized by a narrow window of opportunity for
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annual precipitation during the cool season. In the winters of 2012–2013,
2013–2014, and 2014–2015, a ridge of high pressure off the west coast of
California redirected the normal storm track away from California for several
months during the core of the wet season resulting in a historic drought
(Lund et al. 2018). Conversely, between December 2022 and January 2023,
nine ARs hit California in the longest stretch of continuous AR conditions in
the 70 years that records have been collected (The Atmospheric Rivers
Program 2023).
California's precipitation variability stands out within the conterminous
United States, with dramatic year-to-year fluctuations driven by the wettest
days contributing disproportionately to overall precipitation (Dettinger
2016). The dominance of large storms in California, responsible for
approximately two-thirds of the variance in water-year precipitation, sets the
state apart (Dettinger 2016). Climate-change projections indicate potential
increases in precipitation from the largest storms, underscoring the influence
of these events on the state's regimes of wet and dry spells. Managing these
hydroclimate challenges requires a nuanced understanding of California's
unique precipitation patterns, the impact of atmospheric rivers, and the
evolving dynamics influenced by both natural and climatic factors.
2.2 Historical California Droughts
1976–1977 Drought
The 1976–1977 drought is considered the state’s worst two-year drought
period on record. Statewide runoff in 1977 hit a record low of 15 maf and
was preceded by a dry year. Those conditions contributed to the first time
California water agencies had to prepare for major cutbacks to their water
supplies. The record low in statewide runoff created conditions whereby 47
counties declared local drought-related emergencies and an estimated
125,000 acres of irrigated cropland were fallowed despite a significant
increase in groundwater extraction.
The response to the 1976–1977 drought was multifaceted from many levels
of government. The federal government passed three laws to provide
economic relief with objectives to augment community water supplies,
improve water systems, aid in the purchase and transport of water, and
promote water conservation. The State established a Drought Emergency
Task Force which responded to the drought by utilizing educational
communication and creating legislative and direct assistance approaches.
Chapter 2. California Climate, Variability, and Historical Droughts and Impacts
California Department of Water Resources 2-3
These efforts, combined with a wide publicly accepted conservation effort,
guided the state out of the drought and into subsequent years of wetter
conditions.
1987–1992 Drought
The 1987–1992 drought was a six-year period of dry to critically dry
conditions. The Sacramento Valley experienced four out of six critically dry
water years and two dry water years, while the San Joaquin Valley
experienced all six water years as critically dry. Twenty-three counties
declared local drought emergencies by the end of 1991. During the 1987–
1992 drought, statewide reservoir storage was approximately 40% of
average by the third year of the drought, and it did not return to average
conditions until 1994. SWP allocation was still 100% until 1990, when
allocations for agriculture dipped to 50%. In 1991, SWP allocations dropped
severely to 20% for municipal and industrial and 0% for agriculture. A 1991
governor executive order created a drought action team and directed DWR
to implement a drought water bank. Implementation led to a pilot program
wherein DWR purchased water to deposit into a drought water bank to be
used as needed on an annual basis.
2007–2009 Drought
The 2007–2009 drought was characterized by three consecutive dry or
critically dry water years and the fourth highest total fire acreage of
1.6 million acres in 2008. Unique to this drought was a period of
unprecedented restrictions on diversions from the SWP and federal CVP for
the protection of federal and State-listed fish species in danger of extinction.
The 2007–2009 drought was also the first time a statewide proclamation of
emergency was issued. Compared to past droughts, the statewide hydrologic
conditions during this drought were not extremely severe, but southern
California experienced its single driest year in which parts of southern
California, including the City of Los Angeles, experienced record low
precipitation in 2007.
The area most severely affected by this drought was the west side of the
San Joaquin Valley where CVP deliveries decreased from 50% and 40% in
2007 and 2008, respectively, to 10% of contractors’ allocations in 2009.
SWP deliveries decreased from 60% and 35% to 40% of contractor’s
allocations in 2009. This drought was characterized by water shortages
directly linked to significant economic impacts to agriculture and rural
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communities. The 2007–2009 drought highlighted the need for establishing
methodologies and metrics to assess socio-economic impacts as well as
increasing the understanding and status of groundwater resources. The
State also recognized and established standards for water suppliers to
receive credit for substantial capital investments in urban water conservation
and water management planning.
2012–2016 Drought
Just three years after the previous drought, the 2012–2016 drought was
characterized by the driest four consecutive water years on record for
statewide precipitation, which include two of the warmest calendar years on
record in statewide average temperatures, 2014 and 2015. The drought hit
its lowest record for monthly runoff of 3 inches in 2014. Warmer
temperatures resulted in higher freezing elevations for winter storms, much
of the precipitation falling as rain rather than snow, and increased
evapotranspiration rates. In April 2015, the amount of water stored in
California’s snowpack, referred to as snow-water content, was as low as 5%
of average. The SWP water supply allocations began to decrease during that
period and eventually dropped to a record (at the time) low of 5% in 2014.
This dramatic reduction led to increased groundwater extraction, and
groundwater levels in many parts of the state fell below previous historical
lows. For the first time, satellite imagery revealed the broad spatial extent of
damaging land subsidence occurring throughout the San Joaquin Valley in
response to drought-induced groundwater extraction. San Joaquin Valley
land subsidence rates matched historical record levels, and impacts included
massive tree mortality in the central and southern Sierra, and then-record
levels of wildfire costs.
This prompted the second statewide emergency proclamation for drought.
The State Water Board required a stress test process from water agencies.
In 2016, those stress tests showed that almost 10% of the state’s larger
water systems would need some level of mandated water use reduction over
the next three years, based on a conservative assumption of continued
record dry hydrologic conditions. Additionally, the extent of issues
surrounding drinking water shortages for small rural water systems and dry
private wells was elevated by the severity of water shortage conditions that
occurred during the 2012–2016 drought and beyond. The 2012–2016
drought also reflected an intensification of historically observed drought
impacts and the emergence of new impacts, such as the challenge of
Chapter 2. California Climate, Variability, and Historical Droughts and Impacts
California Department of Water Resources 2-5
maintaining sufficient cold water to support ESA-listed salmonids habitat as
well as increased threats to water quality from harmful algal blooms (HABs).
2020–2022 Drought
The 2020–2022 drought is characterized by three consecutive La Niña
weather patterns that traditionally equate to drier conditions in Southern
California. The La Niña weather patterns produced drier-than-average years
and very low annual runoff. The drought was highlighted by the second year
that the state hit its lowest record of 3 inches for monthly runoff, matching
that of 2014. Snow-water-content levels dropped as low as 35% of average
in April 2022. Reduced snowpack and earlier spring warming led to an 8%
drop in the fraction of spring snowmelt runoff into the Sacramento River and
the San Joaquin River over the past century. Throughout summer 2021,
almost 100% of the state was in drought conditions with approximately 90%
of the state in extreme or exceptional drought conditions. One extreme
outcome from the 2020–2022 drought was the impact on domestic wells.
More than 1,200 domestic wells went dry in 2022, which was almost a 50%
increase from 2021.
Extreme drought conditions during the 2020–2022 drought created a very
dry and arid landscape and produced some of the state’s largest wildfire
seasons on record. In 2020, almost 4.4 million acres burned from more than
9,600 fires, which destroyed more than 10,000 structures. The first giga fire
(a wildfire that exceeds 1 million acres), the August Complex, burned more
than 1 million acres in 2020. In 2021, almost 2.6 million acres burned from
more than 8,800 fires, which destroyed more than 3,600 structures. The
Dixie Fire very nearly became the second giga fire, burning almost 1 million
acres of the SWP’s primary watershed.
The 2020–2022 drought also affected most of the Western United States;
one of California’s water sources, the Colorado River system, saw its water
supply continue to trend downward. During the worsening drought
conditions, the largest storage units in the Colorado River system, Lake
Powell and Lake Mead, had a combined storage of 25% of total capacity in
2022, which was down from 39% in 2021.
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2.3 Uniqueness of California Droughts
From the description of the listed historical droughts above, it is clear that
California’s droughts are not identical, but are unique in their own conditions
and impacts. Some droughts can be localized and affect regions of the state,
while others can be broad and have statewide impacts. Some droughts can
be quick and short, but still challenge management of water supplies, while
others are longer with more exaggerated or extreme impacts. California
droughts can vary by location and scale, periods of time and duration,
climate and landscape conditions, and impacts to communities and
economies. But one current trend of droughts that appears to be consistent
is their magnification by climate change and subsequent heightened impacts.
This danger drives the need for DWR and California to prepare for more
impactful droughts and water shortages in its future.
The wide range of impacts to the environment, landscape, economy, and
people of the state have spurred State government to take additional action
in a variety of ways
to improve the state’s resiliency to droughts and water
supply shortage conditions. Senate Bill 552 requires County governments to
develop drought plans to support small water suppliers and rural
communities that are often frequently affected most by droughts and water
supply shortage conditions. Another example of actions taken are legislative
mandates Assembly Bill 1668 and Senate Bill 606 that require urban water
managers to adopt water shortage contingency plans, drought risk
assessments, and annual water supply and demand assessments.
DWR is
also leading a task force, the Drought Resilience Interagency & Partners
Collaborative, which is a public forum with State and non-State agency
members to advance pre- and post-drought planning actions to build
resiliency to the increasingly arid conditions. The California Water
Commission has developed a white paper, Potential State Strategies for
Protecting Communities and Fish and Wildlife in the Event of Drought
(2024); this paper highlights strategies to address drought and water
shortage impacts, such as integrating groundwater recharge opportunities
with federal- and State-operated reservoir management through the
development of forecast-informed reservoir management, managed aquifer
recharge, and reservoir reoperation to improve the capture and storage of
flood waters for recharge of groundwater basins.
Chapter 3. Analysis of Potential Future Droughts
California Department of Water Resources 3-1
Chapter 3. Analysis of Potential Future
Droughts
A wide array of scientific literature documents the likely impacts of climate
change on California hydroclimate and water resource systems (Vicuna et al.
2007; Dettinger et al. 2015; Diffenbaugh et al. 2015; Ray et al. 2020).
Droughts are likely to be more severe and frequent in the future because of
exacerbating climate change, as well as other factors including increasing
human demands, and increasing environmental demands. Climate change
likely will result in higher temperatures, more variable precipitation, greater
evapotranspiration, and higher sea levels, all of which will impact the SWP
and likely will lead to hydrologic drought conditions that are more stressful
than historical experience in both severity and frequency.
The Delta Adapts Water Supply analysis, completed in 2021 for the Delta
Adapts Climate Change Vulnerability Assessment by the Delta Stewardship
Council, shows that each of these climate stressors will have slightly
different impacts on the SWP. Higher temperatures will result in higher
snowlines, earlier snow melt, and greater evapotranspiration generally
resulting in early peak runoff, lower spring runoff, and greater trade-offs
between flood protection and water supply operations. Lake Oroville plays an
important flood protection role from October to May each year, with the
1970 U.S. Army Corps of Engineers (USACE) Water Control Manual for Lake
Oroville setting forth required flood control storage and flood control releases
needed for downstream flood risk reduction during this time of the year.
Greater evapotranspiration, generally resulting from higher temperatures
but also from changed vapor pressure deficits, results in greater demand for
water from plants (both natural communities and agricultural) and greater
evaporation; these in turn result in reduced soil moisture, deep percolation,
and streamflow downstream. More variable precipitation was shown to
generally have a greater impact on the driest years because dry years tend
to get even drier and more frequent. More variable precipitation is also
expected to result in wetter wet years. These wetter wet years, similar to
what was experienced in 2023, could be so wet that existing export,
conveyance, and storage capacity are fully utilized, and excess water cannot
be managed for beneficial use. Moderate sea level rise (less than 2 feet) was
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shown to have a somewhat subtle but chronic impact on SWP performance.
As sea levels increase, more water is required to maintain compliance with
environmental and water quality regulations in the Delta. The Delta serves
as a transition zone between freshwater from the confluence of the
Sacramento and San Joaquin rivers and saltwater from the Pacific. The
amount of freshwater flowing into and through the Delta drives seasonal and
annual salinity levels. Where freshwater and saltwater meet is referred to as
X2. (X2 is a measurement of distance from the Golden Gate Bridge where
water salinity is 2 parts per thousand of isohaline salt at 1 meter off the
bottom of the waterbed.) A rising sea level threatens the Delta with greater
salinity intrusion by moving the X2 location further east into the Delta
estuary. Counteracting this saltwater intrusion requires increasing the
volume of water released from reservoirs or other tradeoffs, such as salty
water quality.
Where the additional water required to counteract sea level rise comes from
increased releases of upstream storage, it will contribute to lower reservoir
carryover storage, making the system more vulnerable to drought
conditions. Analysis showed that higher levels of sea level rise were strongly
correlated with the most significant water shortage conditions in simulations
of future conditions.
Delta Adapts also included a comprehensive drought analysis of impacts on
Delta water supplies. The analysis looked at both severity of drought impacts
(i.e., the degree to which a historical drought might be exacerbated by
climate change if it were to reoccur under future climate conditions) and
frequency of drought impacts (i.e., the degree to which a historical drought
of a given severity might reoccur more frequently under future climate
conditions). Delta Adapts estimated that under today’s climate conditions
and with the water management infrastructure, operations, regulations, and
current demands, conditions as severe as during the 2012–2016 drought
would only be experienced twice in 1,100 years. Figure 3-1 shows how Delta
exports during that 5-year drought period would compare under current,
2030, and 2050 conditions. Average exports over the 5-year period decline
11.5% below current conditions under 2030 conditions and 18.5% under
2050 conditions. Figure 3-1 also highlights that the worsening conditions of
the drought are not due solely to warmer and more variable conditions
during the drought; exports are also reduced because of the warmer, more
variable conditions of the climate in years running up to the drought. In
Chapter 3. Analysis of Potential Future Droughts
California Department of Water Resources 3-3
September of the year (2011) prior to the start of the drought, storage in
the major North-of-Delta CVP and SWP reservoirs declined as well. Under
current conditions, simulations show more than 8 million acre-feet of water
being carried over from September of the year before the drought into the
first year of the drought.
Under 2030 climate conditions, carryover storage going into the first year of
the drought is reduced by 400,000 acre-feet (5%), and under 2050
conditions carryover storage going into the first year of the drought is
reduced by 760,000 acre-feet or nearly 10%.
Figure 3-1 Declining Delta Exports with Climate Change during
Five-Year Drought
Warming temperatures, more variable precipitation, and higher sea levels all
place additional stress on the water management system and will reduce its
ability to meet all demands. Delta Adapts found that under future climate
conditions, the likelihood of experiencing drought conditions similar to the
2012–2016 drought increase as temperatures increase, sea levels rise, and
precipitation becomes more variable. By 2050, temperatures are expected to
be approximately 2 degrees Celsius warmer than today, precipitation
approximately 12% more variable, and sea levels approximately 1 foot
higher; combined, those conditions would result in drought conditions
State Water Project Long-Term Drought Plan
3-4 California Department of Water Resources
comparable to the drought of 2012–2016 becoming 5 to 7 times more
common.
The 2023 Draft SWP Delivery Capability Report also explores potential future
drought conditions. The SWP Delivery Capability Report models slightly
different conditions than those modeled by Delta Adapts but finds similar
results. The historically experienced drought periods of 1929–34 (6 years),
1976–77 (2 years), 2014–15 (2 years), and 1987–1992 (6 years) all show
increasing severity under 2043 conditions with climate change. Table 1
below, excerpted and adapted from the 2023 Draft SWP Delivery Capability
Report, shows how climate change makes each of the historical droughts
worse. Modeled SWP Table A deliveries are reduced by 10–46% below
deliveries during the same drought with historically experienced conditions
and contemporary regulations. The range of potential decreases is driven by
the conditions of the specific drought and the severity of climate impacts.
Table 1 Estimated Average and Dry-Period Deliveries of SWP Table A
Water (2043 Climate Change Conditions without Adaptation, in
TAF/year) and Percent Reduction in SWP Table A Amount From the
Same Drought With Current Climate Conditions
Period*
2043 Future Climate Change Scenarios
Current
Conditions
50% LOC**
75% LOC**
95% LOC**
(1922–2021)
(1922–2021)
(1922–2021)
(1922–2021)
Long Term
Average
2,238
1,990
1,852
1,770
-11%
-17%
-21%
2 Year
935
623
532
503
(1976–1977)
-33%
-43%
-46%
2 Year
399
357
348
322
(2014–2015)
-11%
-13%
-19%
6 Year
902
644
629
588
(1987–1992)
-29%
-30%
-35%
6 Year
612
543
549
451
(1929–1934)
-15%
-11%
-10%
-26%
* Periods were manually selected to include the driest, most notable,
and most recent years from the simulation.
** LOC= Level of Concern as defined in Draft SWP Delivery Capability
Chapter 3. Analysis of Potential Future Droughts
California Department of Water Resources 3-5
Report. 50% LOC describes a median climate change condition at 2043,
75% and 95% LOC describe increasingly severe and less likely, but
plausible, climate change conditions at 2043.
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3-6 California Department of Water Resources
Chapter 4. SWP Water Supply Allocation Planning and Operations
California Department of Water Resources 4-1
Chapter 4. SWP Water Supply Allocation
Planning and Operations
Drought is a normal part of California’s hydroclimate, and the SWP has
operated through numerous drought periods in the past. Despite this
history, California’s unpredictable climate makes it extremely challenging to
foresee when conditions will slide into drought or when a large storm will
arrive to alleviate drought conditions and recharge reservoirs. To help
anticipate future conditions, the SWP employs a tiered yearly, monthly, and
daily planning and operational scheme to forecast as best as possible this
uncertainty and ever-present risk of drought conditions.
4.1 SWP Annual Allocation Planning
The annual SWP water supply allocation planning cycle begins each year in
November, using information from runoff forecasts. These runoff forecasts
are produced by DWR’s Division of Flood Management (which is independent
of the SWP) starting in December and continuing through May. The runoff
forecasts are used with water supply allocation models and produce water
supply allocation studies that explore possible operational outcomes given
current conditions and forecasted future outcomes. By December 1 of each
year, DWR’s Director issues an initial SWP water supply allocation (in
accordance with the long-term water supply contracts). DWR’s Director may
issue updates to the allocation as conditions evolve throughout the year with
a final allocation issued in May.
4.1.1 Water Supply (Runoff) Forecasts
The runoff forecasts are a key factor in determining the SWP water supply
allocation. Beginning in December, DWR’s Division of Flood Management
(DFM) produces monthly water supply forecasts for the runoff from
Sacramento and San Joaquin watersheds. The runoff forecasts issued
February through May (Bulletin 120 [B120]) incorporate actual snowpack
measurements in addition to precipitation data. These forecasts provide a
probabilistic range of hydrologic outcomes. DWR provides the B120 forecasts
to the public and water agencies on its website. The B120 forecasts are used
by the SWP and many other water managers throughout the state to inform
their water supply planning activities. Water supply forecasts produced by
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4-2 California Department of Water Resources
DWR’s DFM are developed independently so there is no operational or
management overlap between the DFM and the SWP. Although the SWP
contributes funding and operational expertise to the forecasting team, the
SWP does not contribute to forecast calculations or decision-making. This
distinction is important to ensure scientific independence of forecasts and
allow for rigorous and unbiased assessments.
4.1.2 SWP Water Supply Allocation Process
At the beginning of the annual water supply planning cycle (November of
each year), significant uncertainty exists as to the hydrologic conditions for
the water year. So, the runoff forecasts (described above) provide a range of
potential hydrologic conditions that inform SWP estimates of possible
available water deliveries. The SWP develops several allocation studies that
explore the range of potential water supply availability resulting from a
probabilistic range of water supply runoff forecasts provided by DFM. At a
minimum, an average (50% hydrology exceedance) and dry (90% hydrology
exceedance) hydrology are used to inform potential operations and
allocations. Additional information that explains water supply forecasts and
exceedance probabilities can be found on the National Resource
Conservation Service website. The allocation studies also evaluate a range of
potential regulatory requirements that are uncertain and dependent on
hydrology, temperature, and other uncertain conditions.
In consideration of hydrologic uncertainty, the water supply allocation makes
conservative assumptions that precipitation for the remainder of the year
will be much lower than average. Therefore, the study used for allocation
recommendations is based on a dry hydrology assumption of a 90%
exceedance, where there is only a 10% probability that actual conditions will
be drier than the conditions assumed for the study. (A 50% probability
assumes there is even chance that actual conditions will be drier or wetter
by the end of the year.)
Given the changing hydrologic conditions as the water year unfolds, the
studies are updated monthly January through May of each year. If actual
observed hydrology improves, water supply allocation increases may be
issued by DWR’s Director, and the final allocation is typically issued in May.
Decreases in the allocation may be warranted in very dry years but every
effort is made to avoid decreasing the allocation after March.
Chapter 4. SWP Water Supply Allocation Planning and Operations
California Department of Water Resources 4-3
It is important to note that demands for SWP water, which used to fluctuate,
are now largely fixed. In every year since the mid-2000s SWP contractors
have requested their full SWP Table A allocation. Figure 4-1 below shows the
requested and approved SWP Table A deliveries in each year since 1968.
Figure 4-1 Historical SWP Table A Water Amounts requested by
Water Contractors and Approved for Delivery, 1968–2023
4.2 Real-Time Operations
The allocation studies provide a range of forecasted SWP water supply
availability as well as a range of monthly averages of system-wide conditions
(e.g., Feather River releases, Delta outflow, SWP exports, etc.) based on a
range of hydrologies and regulatory requirements. Ranges of forecasts must
be considered because not only are hydrologic conditions subject to change
as the year unfolds, but many regulatory requirements are dependent on
hydrology.
State Water Project Long-Term Drought Plan
4-4 California Department of Water Resources
The actual day-to-day SWP operations (e.g. south Delta exports and Feather
River releases) will differ from those forecasted in monthly operations in
allocation studies because day-to-day SWP operations respond to actual
experienced physical and regulatory conditions. At any given time, the SWP
is operating its facilities to meet the project objectives and priorities (listed
in Section 1 above) as well as manage flood protection throughout the
winter season. Operations are updated weekly and/or daily (and sometimes
even more frequently) based on real-time conditions. Each of these planning
and operational actions is described in greater detail below. These actions
are considered part of the SWP’s drought action plan because they occur in
all years and provide the earliest indications of, and responses to, dry
conditions.
These daily operations address the real-time conditions encountered, such
as hydrologic, meteorological, tidal, and ecological conditions, which deviate
from monthly forecast information and are outside the control of the SWP.
SWP operators meet daily with CVP operators to coordinate and adjust
operations as needed to meet water quality and flow standards required
under D-1641, or flows needed for compliance with State and federal ESA
permit requirements.
Figure 4-2 provides a depiction of how the SWP allocation studies are trued
up with real-time operations.
Chapter 4. SWP Water Supply Allocation Planning and Operations
California Department of Water Resources 4-5
Figure 4-2 SWP Allocation Process and Forecasted Operations
4.3 Additional Allocation and Real-Time Operations
Considerations
Within both the annual allocation planning and real-time operations
decisions, a number of considerations are included in developing the
allocation studies and real-time operations.
4.3.1 Central Valley Project Operations and Coordinated Operations
Agreement
As a condition of their water rights permits, the SWP and Reclamation’s CVP
are jointly obligated to meet flow and water quality requirements to support
in-basin uses — legal uses of water in the Sacramento Basin, including
municipal and industrial, fish and wildlife, agriculture, and recreation. DWR
and Reclamation share the obligation for meeting in-basin uses through a
coordinated operations agreement signed in 1986. This agreement is subject
to periodic review and was most recently amended in 2018. The coordination
of project operations to meet the joint obligations occurs through ongoing
interaction and information sharing, at times requiring multiple interactions
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4-6 California Department of Water Resources
each day. Each allocation study, as well as real-time operations,
incorporates the forecasted and actual operations and conditions of the CVP.
4.3.2 Feather River Requirements
Instream Flow Requirements
Minimum Feather River flow requirements are prescribed in the 1983
“Agreement Concerning the Operation of the Oroville Division of the State
Water Project for Management of Fish and Wildlife” between the CDFW and
DWR (1983 Agreement). At a minimum, the releases from Oroville Reservoir
must meet the monthly instream flow requirements pursuant to this
Agreement.
Typically, during the winter period, when sufficient unregulated flow in the
Sacramento and San Joaquin valley system is present, Feather River
releases will be reduced to conserve water to meet demands later in the
year. But, when conditions are dry or when additional releases are needed to
support Delta exports or in-basin uses (e.g., Delta water quality and flow
standards), Oroville releases will be greater than what is needed to meet the
minimum Feather River instream flow.
The 1970 U.S. Army Corps of Engineers (USACE) Water Control Manual for
Lake Oroville sets forth required flood control storage and flood control
releases needed for downstream flood risk reduction. The storage and
release requirements vary based upon the actual storage, inflow forecasts,
and the wetness of the Feather River watershed. All flood control releases
are coordinated with the USACE and downstream water agencies.
River and Hatchery Temperature Management
Feather River temperature requirements are also prescribed in the 1983
Agreement, as well as in the 2004 biological opinion issued by the NMFS.
Maintaining sufficient storage in Lake Oroville throughout the summer
provides for a more efficient temperature control of reservoir releases,
avoids depleting large volumes of cold water not needed for downstream
temperatures, and conserves the colder water for the later summer and fall
for fisheries.
Chapter 4. SWP Water Supply Allocation Planning and Operations
California Department of Water Resources 4-7
Water removed from deeper in Lake Oroville will have a lower temperature,
and the main intake structure at Lake Oroville allows operators to control the
elevation at which water is removed from the lake.
In wet years, typically there is enough water to manage all temperature
requirements. But, in dry years and hot years, inadequate storage and
warmer lake temperatures often require SWP operators to blend warmer
water being conveyed through the main Hyatt Powerplant intakes with colder
water from the low-level River Valve Outlet System (RVOS). This operation
reduces power generation.
During the drought of 2021, DWR experienced the lowest storage since
Oroville Reservoir was filled for the first time in 1969, surpassing the
historical low in September 1977. Because of the very low storage, the
RVOS was used for blending purposes beginning in June 2021. In August
2021, storage fell below the power pool at about 860 taf, and the RVOS was
the sole means of releasing water to meet downstream purposes.
4.3.3 SWP Storage Targets
Lake Oroville Storage Target
The September 30 carryover planning target for Lake Oroville is currently
1.6 maf. However, in dry years, the 1.6 maf carryover target may not be
achievable because of the low runoff, and storage is compromised to meet
minimum HHS demands, downstream environmental requirements, and
contractual obligations. Carryover storage targets must balance competing
trade-offs between long-term water supply yield of the project and the dry-
year water supply reliability.
SWP San Luis Storage Target
The low-point storage target for the SWP share of San Luis Reservoir is
42 taf. In addition, the SWCs are contractually allowed to carry over a
portion of their annual allocation in San Luis Reservoir, for future water
supply reliability in dry conditions. This additional storage plus the low point
storage of 42 taf is included as a planning target in the allocation studies
beginning in December of each year.
State Water Project Long-Term Drought Plan
4-8 California Department of Water Resources
Southern SWP Storage
Storage in southern reservoirs is generally assumed to be consistent throughout
a one-year cycle, although fluctuations may occur for outages, power resource
contingencies, winter operations and dam safety operations. Larger changes in
storage may occur when southern SWP contractors elect to take flex storage in
Castaic Lake and Perris Lake, as typically occurs in drought years.
4.3.4 State Water Contractor Delivery Requests
The SWCs submit their initial delivery request schedules by early October.
These requests include month by month water deliveries under a range of
assumed allocations such as 30%, 50%, 60% and 100%, but can vary as
needed. The SWCs delivery requests are used as input for allocation studies.
As the water supply allocations are adjusted based on new hydrologic
information, updated delivery schedules are requested and are then used to
inform subsequent allocation studies.
4.4 Regular Communications and Coordination Activities
In connection with SWP’s annual, monthly, and real-time planning and
operational decision-making, the SWP maintains regular communications
with interested parties throughout the year to ensure actions are
coordinated and understood. The following section describes several of the
important communications channels that the SWP maintains during regular
operations, which allows for efficient and rapid ability to step up
communications during droughts.
4.4.1 Water Operations Management Team
The Water Operations Management Team (WOMT) meets weekly during the
fall, winter, and spring, and includes managers from DWR, Reclamation, the
USFWS, NMFS, CDFW, and State Water Board. This structure promotes
regular and consistent coordination among senior managers from these
agencies. WOMT is the regular decision-making body whose task is to ensure
that water project operations comply with both the State and federal ESAs.
If WOMT does not reach consensus on operations, the Directors of those
agencies convene a designated meeting to resolve any issues that WOMT
cannot agree upon.
Chapter 4. SWP Water Supply Allocation Planning and Operations
California Department of Water Resources 4-9
4.4.2 CALFED Operations Group
The CALFED Operations Group meets monthly from October through June of
every year. This group provides a forum to share Delta water management
and fisheries information, but unlike WOMT it is not a decision-making body.
The meetings are facilitated by DWR and are designed to facilitate open
communication to the public about water management activities in the Bay-
Delta being implemented to protect Bay-Delta aquatic species and beneficial
uses of Bay-Delta waters.
At each meeting, staff from Reclamation, DWR, the CDFW, USFWS, NMFS,
and State Water Board provide updates to meeting attendees concerning
SWP and CVP operations, as well as recent activities related to State and
federal ESAs and State Water Board Bay-Delta Water Quality Plan standards
implementation. After each presentation, the opportunity for questions and
answers is available to those in attendance.
4.4.3 State Water Contractors Water Operations Committee Meetings
Monthly, DWR provides briefings to the SWCs that typically include a SWP
water operations overview, SWP allocation study overview, and a contract
administration update. Throughout each year, DWR provides briefings that
consist of SWP operations, hydrology update, Lake Oroville forecasts and
SWP water supply allocation overview.
4.5 Drought Planning Activities
Conducting water operations to meet both water supply and environmental
requirements is especially challenging during extreme and prolonged
drought conditions. Under extreme drought conditions, the combined
upstream water project storage must be utilized to meet critical ecosystem
and human health and safety needs in a manner that balances current needs
with potential future needs until the end of drought conditions. During
consecutive dry years, allocation studies have shown that under continued
dry conditions, there may not be sufficient upstream supply to fully meet all
SWP water supply objectives. These circumstances trigger certain drought-
planning activities pursuant to the SWP’s State and federal ESA permits, and
specific drought actions may be warranted. These activities are further
described below.
State Water Project Long-Term Drought Plan
4-10 California Department of Water Resources
4.5.1 Annual SWP Drought Contingency Planning
The 2020 incidental take permit (ITP) issued by the CDFW to DWR for the
long-term operation (LTO) of the SWP requires the development of a
drought contingency plan under the following conditions:
On October 1, if the prior water year was dry or critical,
Permittee, in coordination with Reclamation, shall meet and
confer with the USFWS, NMFS, State Water Board, and CDFW to
develop a drought contingency plan to be implemented if dry
conditions continue into the following year. On February 1, if dry
conditions continue, Permittee shall submit the drought
contingency plan to the CDFW and shall update the plan monthly
based on current and forecasted hydrologic conditions. If dry
conditions continue, Permittee shall regularly convene this group
to evaluate hydrologic conditions and potential for continued dry
conditions that necessitate implementation of measures identified
in the drought contingency plan for the current water year.
The drought contingency plan solely addresses conditions for the year in
which it is issued. Although the drought contingency plan is a requirement
connected with the SWP’s permit, in recent years (2021 and 2022) the plan
has been coordinated and developed jointly with Reclamation.
Each drought contingency plan typically will include an overview of
hydrological conditions, a species status update, hydrology forecast, SWP
and CVP operations forecast, areas of potential concern, and any drought
actions to be implemented or that may be potentially needed. Recent
experience has shown short-term swings between wet and dry conditions
over the last decade, so the scope of each drought continency plan will
depend on the SWP and CVP conditions and forecasts at that time. The plan
is updated monthly throughout the water year, or until hydrology and
conditions improve such that drought actions are no longer anticipated or
required.
4.5.2 Drought Toolkit
In accordance with the 2019 biological opinions and 2020 ITP, DWR and
Reclamation worked with the WOMT agencies to identify implementable
actions that could be taken during a drought to manage the limited water
supplies of the SWP and CVP. The Drought Toolkit provides a coordination
Chapter 4. SWP Water Supply Allocation Planning and Operations
California Department of Water Resources 4-11
process to implement drought relief actions and identifies potential measures
to be taken during drought years and successive dry years. This Drought
Toolkit describes the coordination, processes, planning and potential drought
response actions in the event of a drought. The coordination process begins
with WOMT. WOMT will request activation of the Drought Relief Year (DRY)
team to assess the potential application of available drought actions and to
plan for future actions if drought conditions persist. The DRY team comprises
technical and policy makers from each of the six WOMT agencies. The DRY
team is also responsible for disclosing the evaluations conducted during any
implemented action for the current water year. The DRY team will, at a
minimum, convene when Shasta cold water pool management is in critical
condition. WOMT, however, may activate the DRY team at its discretion,
based on real-time conditions.
To support an efficient and organized drought response, the Drought Toolkit
contains summaries of potential drought relief actions (DRAs). These
individual action summaries provide DRY team members with a quick
reference that includes both the seasonal timing and implementation times
for rapid evaluation. The Drought Toolkit contains an array of strategies and
is intended to act as a repository of the institutional knowledge gained when
a DRA is implemented. The Drought Toolkit leverages planning and
communication channels to implement actions that can be taken year-round
to support operational flexibility and ongoing habitat and restoration actions
that may bolster the species’ resilience, especially during drought and
successive dry year conditions. As new DRAs are identified and developed,
those DRAs will be evaluated through the LTO coordination process and will
be added to the Toolkit as appropriate. At a minimum, the entire Drought
Toolkit will be revisited no less often than every five years following the
issuance of new biological opinions for the LTO of the SWP and CVP.
The latest version of the Drought Toolkit is available online at the
Reclamation website.
4.6 SWP Operational Drought Actions
When upstream storage is insufficient to fully meet all SWP water supply
objectives, tradeoffs and impacts will occur and drought actions may be
necessary. Management of the SWP during such conditions requires difficult
tradeoffs and informed decision making about the use or preservation of
limited water supplies to minimize near-term and longer-term impacts.
State Water Project Long-Term Drought Plan
4-12 California Department of Water Resources
These tradeoff decisions are made in consultation with other agencies and
attempt to best manage uncertain future conditions.
Throughout the year, drought response actions will change as the year’s
hydrology develops. As noted above, every drought and drought response
will be different. Duration, severity, water storage conditions, and
temperatures are important variables in how a drought unfolds. A subset of
actions from the Drought Toolkit presents a list of historical short-term
drought actions taken during years with limited water supply to meet all
water supply objectives. These decisions serve as examples of drought
actions that may be considered in subsequent drought years. This is not an
exhaustive list nor are actions listed in a particular order.
4.6.1 Human Health and Safety Water Supply Allocation
Under extreme drought conditions and if the forecast indicates an elevated
risk of continuing drought conditions, DWR will allocate available supplies to
ensure that the SWP long-term water supply contractors can meet their
minimum HHS demands, based on minimum water demands for domestic
supply, fire protection, and sanitation needs that cannot be met by other
available water supplies.
4.6.2 One Facility Operation
A one-facility export operation uses either the SWP or CVP facility to export
water from the Delta, and the limited export is distributed between the SWP
and CVP through the intertie between the Delta Mendota Canal and
California Aqueduct. This operation allows the SWP and CVP to limit
upstream releases while maintaining minimum HHS exports. This action was
implemented in 2021.
4.6.3 Facilitation of Transfers and Exchanges
Pursuant to California Water Code Section 1810, the SWP facilitates bona
fide water transfers from sellers to buyers when unused SWP conveyance
capacity is available. Transfer and exchange (which consist of two or more
transfers) are especially important during drought as buyers acquire
additional water from willing sellers to optimize water management and
meet critical needs. Facilitation of transfers and exchanges enable better
storage management and lower energy cost as one can access different
Chapter 4. SWP Water Supply Allocation Planning and Operations
California Department of Water Resources 4-13
sources of water supply when it is available instead of spending extra energy
to extract and replenish within a short period of time.
4.6.4 Water Transfer Delay Programs
In dry and critically dry water years, DWR works with various water agencies
across the state to facilitate water transfers from the Sacramento Valley
through the Bay-Delta to meet south-of-Delta water needs. Water transfers
originating from the Feather River Watershed commonly will be releases from
stored water in Lake Oroville. July through November is the permitted window
to release and export the transfer water. But, in most years, transfers are
moved July through September. In critically dry years, the SWP has delayed
releasing the stored water until the October and November period to bolster
storage during the summer months and conserve cold water pool for the fall
period when cold water releases are critical for the fisheries.
4.6.5 Environmental Actions
The SWP implements a number of actions and monitoring activities to
understand drought effects to the aquatic environment. These actions and
monitoring commitments are implemented to allow SWP scientists to better
understand the system and develop action for implementation in future
droughts. As an example, during the 2020–2022 drought, the SWP increased
its investment in environmental monitoring of drought consequences by
funding monitoring of invasive vegetation and harmful algal blooms. Staff
also collaborated with other agencies within the Interagency Ecological
Program to synthesize existing knowledge of environmental impacts of
drought on the Delta. This project resulted in a technical report and a series
of peer-reviewed journal articles to be published in a special issue of the
journal San Francisco Estuary and Watershed Sciences in March 2024. The
papers concluded with a number of recommendations that may be
implemented by the SWP to reduce the impacts of drought.
The most effective actions to reduce impacts of drought on the environment
are frequently actions taken in non-drought years to increase overall system
resiliency. For example, restoration of tidal wetlands and floodplain habitat
(including that covered by the EcoRestore program) provides benefits to at-
risk fishes and other wildlife in both drought and non-drought periods.
Similarly, the Yolo Bypass Salmonid Habitat Restoration and Fish Passage
(Big Notch) Project will decrease the minimum flows in the Sacramento River
that allow juvenile fish to access critical rearing habitat in the Yolo Bypass.
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To ensure the benefits of restoration and SWP levees are maintained in the
long-term, DWR is investing in assisting the CDFW Nutria Eradication
Program. Drought years are particularly important for making progress in
nutria eradication because droughts limit nutria dispersal.
The SWP is also developing new tools to help respond to the environmental
impacts of drought faster and better. In 2023, DWR piloted a new
cyanobacterial monitoring program using new tools to assess cyanotoxins at
many of the routine monitoring stations throughout the Delta. In
coordination with the USFWS, CDFW, and other State and federal agencies,
DWR also piloted experimental release and population supplementation of
Delta smelt during drought periods when populations usually decline. DWR is
developing environmental DNA and other genetic tools to better monitor at-
risk fishes during their migration through the Delta or at salvage facilities
during drought periods when catch of fish in traditional monitoring programs
is low. Environmental DNA methods are also being piloted to detect new
invasive species more rapidly — invasive species that may become more
easily established during drought periods when native species are stressed.
Longfin smelt have a particularly strong flow-abundance relationship, so they
are particularly hard hit by droughts. The Longfin Smelt Science Program,
mandated by the 2019 ITP, includes efforts to establish a refugial population
in case of catastrophic loss of the wild population, which could occur during
prolonged drought. The program also includes a new longfin smelt outflow
study looking at mechanisms of the longfin smelt outflow abundance
relationship, and a contract with the USFWS and other agencies to create a
new life cycle model for longfin smelt that would, among other things, model
outflow effects on longfin smelt abundance.
4.7 Statewide Drought Actions Supported by the SWP
4.7.1 West False River Drought Salinity Barrier
The West False River Drought Salinity Barrier (WFR Drought Barrier) was
installed by DWR in 2015 and again in 2021–2022, both under Governor
Drought Emergency Proclamations. The purpose of the barrier is to mitigate
salinity intrusion in the central Delta and protect the beneficial uses of Delta
water. The barrier has been proven effective to preserve water quality in the
Delta when releases of fresh water from upstream reservoirs are reduced.
Although the barrier provides incidental benefit to SWP operations, which are
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California Department of Water Resources 4-15
minimal during extreme drought, the benefits of the barrier to in-Delta water
users and ecological conditions are much broader.
Installation of the WFR Drought Barrier was accompanied by a robust
environmental monitoring program, including monitoring for impacts of the
barrier on salmonid migration, predation rates, harmful algal blooms, and
aquatic weed distribution. Future installations of the WFR Drought Barrier
and similar drought actions also should be accompanied by environmental
monitoring.
4.7.2 Temporary Urgency Change Petition
The submittal of a temporary urgency change petition (TUCP) is an
emergency adaptation strategy provided for within the California Water
Code. Through the submittal of a TUCP, DWR and Reclamation jointly
request that the State Water Board consider a temporary modification of
Delta water quality and flow standards contained in D-1641. Such requests
are made when forecasting and modeling indicate that continuing to meet D-
1641 standards in the near term will result in more severe impacts to water
quality and aquatic resources later in the year, and that the most prudent
course of action in the near term is to preserve water storage for late season
temperature management, instream flow, water quality, and Delta outflow
later in the year. TUCPs have been submitted and conditionally approved by
the State Water Board in 2014, 2015, 2021, 2022 and 2023.
4.7.3 State Water Contractor Conservation Actions
During drought conditions, DWR regularly communicates with its customer
agencies regarding expected conditions and SWP operations. This
information is intended to support these agencies as they make their own
drought response decisions including the degree to which to implement
water conservation actions. During periods of extreme drought, DWR will
also communicate publicly with its member agencies to encourage specific
conservation actions or targets. In addition to DWR communications on
expected conditions, SWP contractors who are required to develop Urban
Water Management Plans are also required to adopt Water Shortage
Contingency Plans (WSCP). The plans include required conservation actions
when specific water shortage conditions occur.
State Water Project Long-Term Drought Plan
4-16 California Department of Water Resources
4.7.4 Review of State Curtailment and Transfer Policies
DWR, as a part of a statewide drought action, prospectively considers State
Water Board policies governing water right curtailments and water transfers.
DWR assesses these policies within the context of DWR's role both broadly in
supporting the state's water needs and as owner/operator of the SWP and its
roughly 28 million water users. Where DWR identifies challenges or
inconsistencies with state needs, it coordinates with the State Water Board.
4.8 Limits and Tradeoffs of Extreme Drought
In any given extreme drought condition, the SWP and CVP must respond to
short-term crisis conditions while continuing to preserve the operational
flexibility to respond to future, long-term conditions, should prolonged
drought conditions continue. Because the end of drought conditions cannot
be predicted, operations must be conducted in a manner that balances
current needs with potential future needs. Consequently, there are inevitable
tradeoffs that must be made in managing water project operations during a
prolonged drought. Decisions are made after full consideration of all the pros
and cons of any potential action. These decisions require the full and
balanced consideration of the benefits and the impacts of the action on the
natural environment and human activity.
Chapter 5. Lessons Learned from the 2020–2022 Drought Emergency
California Department of Water Resources 5-1
Chapter 5. Lessons Learned from the
2020–2022 Drought
Emergency
Although each drought is unique and poses its own challenges and requires
its own customized response to conditions and impacts, new knowledge and
experience is gained with each new drought event. Capturing and preserving
these lessons is an important element of the SWP’s efforts to continuously
improve drought management and plan for more severe future droughts. A
high-level summary of the lessons learned from the 2021–2022 drought is
provided below.
5.1 Communication
Early and consistent communication with the public and water agencies is
critical to aligning drought response efforts. The SWP’s operational decisions
and announcements on water allocations occur at regular intervals, starting
in December with an initial allocation and concluding in May with a final
allocation. But Central Valley farmers make their planting decisions for the
next year in October and November. These decisions have a high impact on
demand for SWP water. SWP staff recommends that communications be
increased early in the water year and maintained throughout the season
between SWP allocations. If conditions are well below average, in
anticipation of a dry year, communication on water conservation with the
SWP contractors should start well before the initial allocation.
5.2 Temporary Urgency Change Petitions
California’s hydrologic conditions are dynamic, uncertain, and can change
from month to month. The need for a TUCP often becomes clear only weeks
before it is needed. SWP staff concluded that while TUCPs were processed
relatively quickly, it was rarely possible to observe the full public review
timelines that are otherwise required. SWP staff recommend working with
the State Water Board to identify opportunities to streamline processes
related to TUCPs, and to engage in the WQCP process so that future TUCP
needs can be planned for, to the extent possible.
State Water Project Long-Term Drought Plan
5-2 California Department of Water Resources
5.3 Delta Barriers
The SWP implemented or considered a series of temporary rock barriers in
the Delta to mitigate salinity intrusion during the drought emergency. These
barriers were a component of preventing saltwater intrusion as less fresh
water was released from upstream reservoirs into the Delta to preserve
water storage critical for HHS. Salinity intrusion threatens Delta agriculture,
local municipal supplies, the natural environment, as well as the supply of
drinking water south of the Delta.
From June 2021 to November 2022, the SWP installed a drought salinity
barrier at West False River in the Delta. The barrier was successful at
mitigating salinity intrusion and likely will be needed again based on the
cyclical nature of drought in California. The SWP also planned to implement
drought salinity barriers in the north Delta if drought conditions continued to
worsen after the 2022 water year. Barriers were planned to be implemented
as early as June 2023 at Miner Slough and Steamboat Slough but were not
needed as record snowfall in 2023 alleviated drought conditions.
Because the WFR Drought Barrier has proven an effective drought measure
and is expected to be needed again during future droughts, DWR is working
toward a longer-term plan for the periodic and severe drought-based
installation of the barrier. This effort is allowing DWR to work with permitting
agencies in a more proactive manner (See description in Chapter 7.)
Funding the continued study of HABs in and around Franks Tract in the Delta
will help identify and understand the growth of HABs in the area.
5.4 Aqueduct Reverse Flow Operations
The SWP examined several proposals to deliver water stored south of SWP’s
major reservoirs by reversing the flow in SWP aqueducts. These proposals
were considered to protect HHS if 2021 was followed by another critically dry
year. Kern County Water Agency and Dudley Ridge Water District requested
that DWR consider a proposal to reverse the flow in the California Aqueduct
by closing check site gates and pumping around the check site to deliver
water to these agencies from the Cross Valley Canal and Kern Water Bank as
far upstream as Check 20. In addition, the South Bay water contractors
requested consideration of a proposal to reverse the flow in the California
Chapter 5. Lessons Learned from the 2020–2022 Drought Emergency
California Department of Water Resources 5-3
Aqueduct as far upstream as Bethany Reservoir to deliver water from
Semitropic Water District to these agencies.
Ultimately, both proposals were ruled out as either infeasible because of a
mix of technical, financial, operational, and legal considerations or were
found to be unnecessary as water could be delivered by a series of
operational exchanges among water contractors. SWP staff recommends
that the feasibility of these projects be reexamined during future drought
emergencies as a potential solution during a scenario where no water is
flowing through the aqueduct. Operational exchanges are typically always
possible and preferred in any other circumstance.
State Water Project Long-Term Drought Plan
5-4 California Department of Water Resources
Chapter 6. SWP Actions to Improve Long-Term Drought Resilience and
Add Flexibility, Efficiency, and Capacity
California Department of Water Resources 6-1
Chapter 6. SWP Actions to Improve Long-
Term Drought Resilience and
Add Flexibility, Efficiency, and
Capacity
In addition to management actions taken during drought conditions, the
SWP is also investigating, developing, and implementing several projects
that will add flexibility, efficiency, and capacity to the SWP to make the
project more resilient to future droughts. The following sections describe
several major investments to improve the SWP.
6.1 Delta Conveyance
Infrastructure built to accommodate seasonal patterns of the past cannot
accommodate weather extremes and flashy winter flows that are becoming
more common. The Delta Conveyance Project is a proposed infrastructure
modernization project outlined in Governor Newsom’s strategy to adapt
California’s water supply for a hotter and drier future. The project is
essential to adapting to climate-driven weather extremes and in helping to
ensure that the SWP can capture, move, and store water during extreme
weather events, including extended drought conditions. Modernizing SWP
infrastructure in the Delta would provide an added tool to capture water
from brief yet high-flow and fast-moving storms, and place that water in
storage for later use. This added level of flexibility is meant to better
manage periods of drought and provide much-needed drought relief.
For example, if the Delta Conveyance Project had been operational during
the high rain events of January 2022 and 2023, a modernized conveyance
system could have conveyed additional water into San Luis Reservoir while
still meeting fishery and water quality protections and regulations. On
December 21, 2023, DWR certified the final Environmental Impact Report.
This important step marks the completion of
an extensive environmental
review. Through the environmental review process, DWR selected the
“Bethany Reservoir Alignment” for further engineering, design, and
permitting.
State Water Project Long-Term Drought Plan
6-2 California Department of Water Resources
6.2 California Aqueduct Subsidence Program
Overdraft of the San Joaquin Valley groundwater aquifers has caused land
subsidence for the San Luis Canal and the California Aqueduct, resulting in a
diminished ability of this backbone infrastructure to provide the flexibility
and resiliency needed to address greater hydrologic variability. Because of
the differential subsidence, the conveyance system has experienced a loss of
operational flexibility and an overall average conveyance capacity reduction
of 20%, with particularly affected locations experiencing 45% constrictions
in flow.
In 2019, the California Aqueduct Subsidence Program (CASP) was
established as an initiative of the SWP to work in conjunction with
Reclamation, the owner of the San Luis Canal for the CVP, to develop and
implement preventive and corrective measures to mitigate the effects of
subsidence, while planning the remediation of anticipated future subsidence.
Reestablishing the conveyance capacity of the system that has been lost
over time to subsidence will allow the system to efficiently capture and
convey the more extreme hydrologic flows expected in California’s hotter,
drier future. Although this action will primarily affect operations during wet
periods and peak flow events, the water conveyed and stored during these
operations will provide critical water supplies during drought, improving the
resilience of the CVP and SWP conveyances to climate change and drought.
6.3 Forecast-Informed Reservoir Operations
Recognizing the importance of atmospheric rivers in a changing climate,
DWR in partnership with Yuba County Water Agency; the Center for Western
Weather and Water Extremes (CW3E) at the University of California, San
Diego; USACE; the National Weather Service; and other members of the
Yuba-Feather Steering Committee are developing a forecast-informed
reservoir operations (FIRO) program at New Bullards Bar on the Yuba River
and Lake Oroville on the Feather River. FIRO is a flexible water management
strategy that uses improved weather and runoff forecasts to help water
managers retain or release water from reservoirs to increase resilience to
droughts and floods. The primary objective of this FIRO project is to reduce
flood risk; a secondary objective is to achieve water supply benefits where
possible, while supporting environmental needs.
Chapter 6. SWP Actions to Improve Long-Term Drought Resilience and
Add Flexibility, Efficiency, and Capacity
California Department of Water Resources 6-3
FIRO has the potential to improve drought resilience by allowing reservoir
operators to retain additional water in storage that otherwise would be
released had forecasts indicated the absence of flood-threatening storms on
the horizon. In addition, longer lead forecasts used in FIRO often result in
water being released from reservoirs in advance of approaching storms to
create additional storage space for storm flows. The water released can then
be diverted into other storage reservoirs (likely groundwater basins) over a
longer period than would have been available without FIRO. This action
results in additional water in downstream storage basins that can be used to
support water needs during a drought.
6.4 Storage Investigations
The SWP Storage Investigation Initiative is an ongoing phased activity to
identify, investigate, and develop potential water storage opportunities for
the SWP throughout the state that could be used to store additional water
during wet years for use during dry conditions. The focus of this initiative is
on groundwater storage opportunities, but surface water projects could be
considered if appropriate locations can be identified.
As of 2023, this initiative has focused on two specific areas for further
evaluation and refinement: (1) west slope of the Sierra Nevada mountains
along the San Joaquin River and tributaries and (2) south-of-Delta SWP
conveyance-connected areas. The current phase of investigation involves
modeling of existing and future projected conditions to estimate the volume,
timing, and frequency of available water that could be safely diverted into
storage within all regulatory, environmental, and physical system constraints.
New storage added to the SWP would act as both a climate resilience and
drought resilience action because it would add flexibility and new operational
capabilities to the SWP system, allowing the system to take advantage of
wet conditions that produce excess flows and save that water for use during
dry conditions.
State Water Project Long-Term Drought Plan
6-4 California Department of Water Resources
6.5 Evaluation and Adjustment of Oroville Carryover Storage
Targets
The Oroville carryover storage target will be reviewed and may be updated if
warranted by changed conditions. Examples of changed conditions include:
•
Physical capacities (examples include the outlet capacities at Lake
Oroville).
•
Operating regulations upstream or in the Delta (Feather River
temperature requirements or new State Water Board or State ESA or
federal ESA requirements, for example).
•
Operating agreements (such as the Coordinated Operations Agreement
with Reclamation).
•
New tools for assessing observed changes to hydrology.
6.6 SWP Enhanced Asset Management
Continued enhancement of existing asset management practices as described
in the 2023 Operations and Maintenance Strategic Asset Management Plan
(SAMP) is an ongoing effort to review, document, improve and embed
strategies, processes and tools for the monitoring, inspection, condition
assessment, maintenance, renewal, risk management, and long-term
planning for SWP water storage and conveyance infrastructure. Updating
those business processes with documented processes and tools to support
risk-informed decision-making processes will enhance SWP infrastructure
reliability and assist operations and maintenance staff in modifying
operations strategies, maintenance programs, and reprioritizing planned
capital projects as hydrologic conditions change. This effort will allow DWR to
preserve and maximize the operational flexibility that was built into the SWP
when it was constructed, thereby allowing DWR to reliably capture and move
water into storage when it is available, then deliver available project and
non-project (transfer) water during extreme drought conditions.
6.7 DWR Climate Action Plan
DWR established a climate change program in 2008 and released
progressive phases of its Climate Action Plan in 2012, 2018, 2019, 2020,
and 2022. Each phase of the plan provides cutting-edge analysis and
responses to climate change challenges and explores how DWR will respond
to these challenges.
Chapter 6. SWP Actions to Improve Long-Term Drought Resilience and
Add Flexibility, Efficiency, and Capacity
California Department of Water Resources 6-5
Phase II of the Climate Action Plan (2018) lays out a systematic and
comprehensive DWR-wide policy for screening and, if necessary, evaluating
the resiliency of DWR projects to climate change. This process mainstreams
the consideration of climate and drought risks in DWR projects and ensures
that ongoing and future investments have considered the risks of a hotter-
drier climate before they are built.
Phase III of DWR’s Climate Action Plan, published in 2019 and 2020,
assessed climate change vulnerability and outlines DWR’s strategy for
adapting to the impacts of climate change. This phase helped prioritize DWR
resiliency efforts, such as infrastructure improvements, enhanced
maintenance and operation procedures, revised health and safety
procedures, and improved habitat management, and it laid out additional
steps needed to continue adaptation implementation.
6.8 SWP Climate Change Resilience Planning
Long-term drought resilience and climate change resilience are closely
related, as climate change is expected to intensify California’s natural
drought cycles. Tiering off DWR’s Adaptation Plan, an SWP climate change
adaptation analysis will be finalized in 2024 and will document the degree to
which several major projects, that are currently in the planning phase, will
help the SWP adapt to climate change — including more severe and frequent
droughts. This analysis will evaluate a range of climate conditions and
adaptation combinations. The SWP will use this analysis to further refine its
long-term adaptation goals and strategies and the degree to which the
adaptation project portfolio reduces drought risks under future climate
conditions.
6.9 Climate Change and Drought Risk Communication
The SWP has a long history of providing climate change and drought risk
information to the public and water agencies that use SWP water supplies.
DWR has been incorporating estimates of climate change impacts on SWP
deliveries since 2009 in the bi-annual SWP DCR. This report provides
estimates of average and multi-year dry and wet conditions deliveries under
future climate conditions. Public water agencies use this information in their
planning and water resource portfolio development. In the 2023 Risk-
Informed Future Climate Scenario Development for the State Water Project
Delivery Capability Report, DWR made significant improvements to the
State Water Project Long-Term Drought Plan
6-6 California Department of Water Resources
information it provides to the public and public water agencies that use SWP
water.
Major improvements included:
1.
Development and inclusion of a climate-adjusted historical hydrology
scenario that replaces the historical hydrology record as the baseline
for current conditions. This improvement explicitly captures and
accounts for changes in climate that have already occurred and
provides a more accurate hydrological sequence for estimating current
SWP delivery capability. This scenario indicates that the SWP has
already lost approximately 2% on average of its annual delivery
capability from climate changes that have already occurred. These
impacts are even more pronounced in dry years.
2.
Development and inclusion of new system risk-informed future climate
scenarios that provide greater exploration of uncertain future
conditions, including more extreme droughts and extreme wet events.
These new scenarios explore conditions 20 years into the future with
up to 1.8 degrees Celsius warming, 2% less average precipitation,
13% more extreme precipitation, and 30 centimeters of sea level rise.
These scenarios will guide DWR and public water agencies toward
greater climate and drought resilience and provide greater
transparency to water users about expected reductions in future water
supply and uncertainties in the magnitude of expected reductions. The
DCR climate change scenarios indicate that by 2043, the SWP will lose
an additional 11% to 21% of its delivery capability if no adaptation
actions are taken.
3.
DWR conducted an independent peer review through the Delta Science
Program of the science underlying both the climate-adjusted historical
hydrology scenario and the future climate scenarios. This additional
effort included review by three independent experts. As a result,
several improvements and additions were made to the development of
the scenarios. Further, the review should provide users of the DCR
scenarios with increased confidence that the analysis is best available
science for decision-making.
The 2023 DCR also provides important new drought information. It shows
that if a future two-year drought occurred similar to that of the 1976–1977
drought of record, but with intensified conditions resulting from expected
Chapter 6. SWP Actions to Improve Long-Term Drought Resilience and
Add Flexibility, Efficiency, and Capacity
California Department of Water Resources 6-7
climate changes by 2043, SWP water deliveries would decline 33% to 50%
below present-day delivery capability. The report also explores multiple
one-year and six-year drought periods.
State Water Project Long-Term Drought Plan
6-8 California Department of Water Resources
Chapter 7. Actions to Improve Long-Term Drought Resilience and Add Flexibility,
Efficiency, and Capacity that SWP Supports and Contributes Toward
California Department of Water Resources 7-1
Chapter 7. Actions to Improve Long-Term
Drought Resilience that SWP
Supports and Contributes
Toward
7.1 West False River Drought Salinity Barriers Programmatic
Approach
During severe drought conditions that result in significantly decreased
natural flows into the central Delta, increased needs and challenges arise
with preserving upstream impounded water for health, safety, and
regulatory uses while preventing salinity intrusion into the central Delta.
During normal water years, natural flows and flows from upstream reservoirs
into the Delta prevent San Francisco Bay saltwater from entering the central
Delta. But, during previous severe drought conditions there was a significant
risk of San Francisco Bay saltwater flows entering the central Delta. If this
were to occur, it would take years for the central Delta salinity levels to
return to normal. To prevent such an event under previous severe drought
conditions, DWR installed a temporary drought salinity barrier in the Delta’s
West False River. Based on data from these previous installations, the WFR
Drought Barrier has proven an effective tool for reducing saltwater intrusion
into the central Delta. Given the current scientific understanding of the
cyclical nature of drought in California, DWR anticipates having to reinstall a
WFR Drought Barrier up to two times over the next 10 years. DWR is
finalizing an environmental impact report and working to secure all
necessary environmental permits to reinstall the barrier when needed. Doing
this work ahead of time will reduce or eliminate the need for last-minute
emergency actions to install the barrier.
The WFR Drought Barrier would be constructed in the central Delta in West
False River, a main channel located west of and connected to Franks Tract.
By hydraulically blocking West False River, flows into Franks Tract would be
mostly from the less-salty Old River farther upstream on the San Joaquin
River, rather than farther downstream on the San Joaquin River, where it is
more influenced by saltier San Francisco Bay water. The barrier would
State Water Project Long-Term Drought Plan
7-2 California Department of Water Resources
protect against saltwater intrusion into the central Delta and consequently
help maintain central Delta water quality. Without the protection of the
drought salinity barrier in West False River — a critical location for
preventing salinity intrusion into the central Delta — during a severe
drought, saltwater intrusion could render Delta water unusable for
agricultural needs, reduce the value of habitat for aquatic species, and affect
more than 27 million Californians who rely on the Delta for at least a portion
of their water supply.
During severe drought without the barrier in place at this critical location,
the saltier water carried through West False River would gradually
contaminate the fresh water in Franks Tract. The central Delta would be
filled with salts, a condition that cannot be reversed during drought
conditions. Consequently, until the salts could be flushed from the central
Delta, the salinity intrusion would create long-term impacts on the many
beneficial uses of central Delta water.
7.2 Improved Seasonal Forecasting
DWR has been pursuing improvements to its forecasting capabilities for
more than a decade through collaborative work with local and federal
agencies and the research community. These efforts have been focused in
two areas: (1) work to develop improved forecasting tools supporting
emergency response to hydrologic extremes and snowmelt forecasting, and
(2) improvements in seasonal forecasting capabilities to support resource
and program planning within a given water year and in a multi-year
environment related to recurring drought conditions. Each area of
investment is described below.
Area 1 — Improved Forecasting Tools Supporting Hydrologic Extremes
Response and Snowmelt Forecasting
Throughout the past decade, a number of efforts have been in play to
update and improve the tools used for runoff forecasting for river forecasting
time frames (zero to five days) and seasonal runoff forecasting associated
with Bulletin 120 (April through July snowmelt volume forecasting).
Improved observations have been undertaken by investing in remote
weather station upgrades, including more gridded data products in the
forecast process, and developing remote snow water-equivalent
observations and associated physically based snowpack and watershed
runoff modeling. Currently, funding is available to provide airborne snow
Chapter 7. Actions to Improve Long-Term Drought Resilience and Add Flexibility,
Efficiency, and Capacity that SWP Supports and Contributes Toward
California Department of Water Resources 7-3
mapping up to four times per year for approximately two-thirds of the
watersheds that appear in the monthly B120 forecast of snowmelt runoff
from April through July. In addition to the data collection, iSnoBal snowpack
modeling and WRF-Hydro runoff modeling is being developed for these
watersheds. In addition to these modeling efforts, additional watershed
models are being developed using USACE models to support river and
reservoir forecasts. An experimental research watershed model for surface
water availability for the Sacramento watershed is also in development.
Area 2 — Improved Seasonal Forecasting for Operational and Governance
Planning
DWR has spent the past decade assembling a coalition of researchers to
begin to systematically address opportunities to improve seasonal forecast
capabilities, as well as to address known challenges that limit long-term
predictability. The group meets annually in November to examine water year
outlook experiments and again in summer to review outcomes and develop
next research steps. Sponsored by DWR, the Center for Western Weather
and Water Extremes posts to their website subseasonal-to-seasonal
experimental (S2S) forecast models for public viewing. Additional S2S
forecasting information is provided on the S2S Coalition website.
Although some progress has been made to find forecasts of opportunity —
where the climate system aligns to enable a more reliable forecast —
additional work is needed to better inform long-term forecasting.
7.3 Continuing Commitments to Environmental Resiliency
The SWP continues its commitment to enhance aquatic ecosystems to
increase resilience to future droughts through habitat creation, scientific
exploration to inform successful management for beneficial environmental
outcomes, and improved monitoring of changing conditions.
Habitat-creation projects include restoration of tidal wetlands, floodplains,
and rearing habitat for juvenile salmonids as part of the proposed Healthy
Rivers and Landscapes Program
and other efforts. All of DWR’s habitat
restoration activities are being evaluated under a science-based adaptive
management framework for continuous improvement to learn how to better
design and implement restoration for maximum environmental benefits.
State Water Project Long-Term Drought Plan
7-4 California Department of Water Resources
The SWP is also researching the feasibility of many voluntary actions
included in the Delta Smelt Resiliency Strategy (California Natural Resources
Agency 2016) and Sacramento Valley Salmon Resiliency Strategy (California
Natural Resources Agency 2017). Delta smelt Resiliency actions include
contracting with the University of California, Davis, to research the potential
benefits of operating managed wetlands in Suisun Marsh for production of
fish food, researching potential benefits of fall flow pulses in the Yolo Bypass
(Davis et al. 2022), and collaborating on research into aquatic weed
monitoring and management (Rasmussen et al. 2022). Actions to improve
salmonid resiliency include removal of fish passage barriers, improvements
to the Yolo Bypass, and construction of a permanent non-physical barrier at
Georgiana Slough. Although none of these actions are specifically targeting
droughts, all are designed to increase the resiliency of at-risk fish
populations to future climatic variability.
More recently, the California Salmon Strategy for a Hotter, Drier Future was
released to guide progressive actions that the State can take to support
resilient salmon populations as the climate changes. For the SWP, many
Salmon Strategy actions focus on the Feather River because of the focus of
operations there, the presence of the Feather River Hatchery, and the
presence of a population of State and federally listed spring-run Chinook
salmon. The SWP is already working to advance the California Salmon
Strategy with several measures on the Feather River. The Strategy calls for
evaluation of reintroduction of salmon to historical cold-water habitats in
upstream regions above dams in order to establish populations in refuge
habitats (Action 1.6). In 2023, DWR initiated a pilot program for re-
introduction of Spring-run in the North Fork of the Feather River, above Lake
Oroville. Studies are underway assessing the feasibility of introducing egg
and juvenile life stages. Also, in keeping with Goal 1 of the Strategy to
Remove Barriers and Modernize Infrastructure for Salmon Migration, the
SWP is working to remove Sunset Pumps, a long-standing impediment to
salmon upstream and downstream migration and predator attractant in the
Feather River. Finally, DWR is working on Goal 4 (Modernize Salmon
Hatcheries) with partner agencies by working to install a water treatment
system at the Feather River Hatchery (Action 4.8) to improve in-hatchery
survival from egg to release stages, effectively boosting the release numbers
and increasing efficiency. DWR is also working with CDFW to develop a
Hatchery Genetic Management Plan for Feather River Hatchery, which would
Chapter 7. Actions to Improve Long-Term Drought Resilience and Add Flexibility,
Efficiency, and Capacity that SWP Supports and Contributes Toward
California Department of Water Resources 7-5
ensure adoption of best practices to minimize harm to wild salmon
populations (Action 4.13).
The experimental release of hatchery-raised Delta smelt conducted during
the 2021–2022 drought years is continuing, with the SWP helping to design
releases conducted by the U.S. Fish & Wildlife Service that will
experimentally inform the growing supplementation program.
Supplementation of wild fish with hatchery-raised Delta smelt has risks
(Lessard et al. 2018), but may provide a necessary buffer to the population,
particularly during droughts. Longfin smelt culture and propagation methods
are also under development within the Longfin Smelt Science Program in the
event that this species also needs a refuge population against future climatic
extremes.
Recently, SWP began using innovative genetic technology to assist in rapidly
and accurately identifying Chinook salmon runs (i.e., Fall, Late-Fall, Winter,
Spring) to protect endangered runs (Winter and Spring-runs) and guide
water operations in the Delta. Genetic run assignment enables increased
confidence in identification results compared to traditional run assignment
methods based solely on the length of the fish and helps ensure that water
capture is not restricted unless an endangered fish is present. False
identification by visual inspection can result in unnecessary reductions in
water supply exports. By improving salmon run assignment, SWP can
provide a more reliable water supply, especially during droughts, without
compromising protections for endangered species.
Harmful cyanobacterial blooms are one of the clearest environmental
impacts of droughts, and extensive research, monitoring, and collaboration
are needed to identify and implement mitigation and continued monitoring.
To that end, the SWP is working with multiple water boards, the Delta
Science Program, and other agencies to develop a monitoring framework for
harmful cyanobacteria in the Delta.
7.4 North Delta Barriers
DWR has completed extensive planning and design in support of potential
north Delta drought salinity barriers during extreme drought conditions.
Drought barriers in the north Delta provide salinity management benefits in
the interior Delta by blocking the flow of water from the Sacramento River
into Steamboat and Sutter sloughs, thus allowing more flow to remain in the
State Water Project Long-Term Drought Plan
7-6 California Department of Water Resources
Sacramento River and pass through Georgiana Slough. This action helps to
repel salinity intrusion into the interior Delta with the release of less water
from upstream reservoirs. To reduce the potential impacts to north Delta
agricultural diverters and potential impacts to their diversions, DWR moved
the location of the drought barriers as far downstream as possible. The
locations of the potential barriers are now proposed for Miner Slough on the
north side of Ryer Island and Steamboat Slough on the south side of Ryer
Island.
To support barrier design, DWR has completed extensive geologic
explorations at the proposed barrier sites, and these explorations are being
used for the geotechnical engineering design. Additionally, DWR has
completed hydrodynamic modeling and begun the application process for
necessary permits. DWR intends to complete the long-lead planning and
permitting steps for this project so that if North Delta barriers are needed
during a future drought, a project could be implemented quickly and
efficiently.
Chapter 8. References
California Department of Water Resources 8-1
Chapter 8. References
California Natural Resources Agency. 2016. Delta Smelt Resiliency Strategy,
July 2016. Sacramento (CA). 13 pp. [Government Report.] Viewed
online at: https://resources.ca.gov/CNRALegacyFiles/docs/Delta-
Smelt-Resiliency-Strategy-FINAL070816.pdf. Accessed: Feb. 9, 2024.
California Natural Resources Agency. 2017. Sacramento Valley Salmon
Resiliency Strategy, July 2017. Sacramento (CA). 16 pp. [Government
Report.] Viewed online at: http://resources.ca.gov/docs/Salmon-
Resiliency-Strategy.pdf. Accessed: Feb. 9, 2024.
California Water Commission. 2024. Potential State Strategies for Protecting
Communities and Fish and Wildlife in the Event of Drought.
Sacramento (CA). 33 pp. [Government Report.] Viewed online at:
https://cwc.ca.gov/-/media/CWC-Website/Files/Documents/
2024/01_January/Drought-Strategies-White-Paper_Final.pdf.
Accessed: Feb. 9, 2024.
Davis B, Adams J, Bedwell M, Bever A, Bosworth D, Flynn T, Frantzich J,
Hartman R, Jenkins J, Kwan N, MacWilliams M, Maguire A, Perry S,
Pien C, Treleaven T, Wright H, Twardochleb L. 2022. North Delta Food
Subsidy Synthesis: Evaluating Flow Pulses from 2011-2019.
[Government Report.]
Dettinger M. 2016. “Historical and Future Relations Between Large Storms
and Droughts in California.” San Francisco Estuary and Watershed
Science. Volume 14 (Issue 2). 21 pp. [Journal.] Viewed online at:
https://escholarship.org/uc/item/1hq3504j. Accessed: Feb. 20, 2024.
Dettinger M, Udall B, Georgakakos A. 2015. “Western water and climate
change.” Ecological Applications. Volume 25 (Issue 8): Pages 2,069–
2093. [Journal.] Viewed online at: https://doi.org/10.1890/15-0938.1.
Accessed: Feb. 22, 2024.
State Water Project Long-Term Drought Plan
8-2 California Department of Water Resources
Dettinger MD, Ralph FM, Das T, Neiman PJ, Cayan DR. “Atmospheric Rivers,
Floods and the Water Resources of California.” Water. Volume 3 (Issue 3):
Pages 445–478. [Journal.] Viewed online at: https://www.researchgate.
net/publication/50848697_Atmospheric_Rivers_Floods_and_the_Water_
Resources_of_California. Accessed: Feb. 22, 2024.
Diffenbaugh NS, Swain DL, Touma D. 2015. “Anthropogenic warming has
increased drought risk in California.” Proceedings of the National
Academy of Sciences. Volume 112 (Issue 13): Pages 3,931–3,936.
[Journal.] Viewed online at: https://doi.org/10.1073/pnas.
1422385112. Accessed: Feb. 21, 2024.
Jay L, Medellin-Azuara J, Durand J, Kathleen S. 2018. “Lessons from
California’s 2012–2016 Drought.” Journal of Water Resources Planning
and Management. Volume 144 (Issue 10): 13 pp. [Journal.] Viewed
online at: https://watershed.ucdavis.edu/sites/g/files/dgvnsk8531/
files/products/2021-05/%2528ASCE%2529WR.1943-5452.0000984.
pdf. Accessed: Feb 8, 2024.
Lessard J, Cavallo B, Anders P, Sommer T, Schreier B, Gille D, Schreier A,
Finger A, Hung TC, Hobbs J, May B, Schultz A, Burgess O, Clarke R.
2018. “Considerations for the Use of Captive-Reared Delta Smelt for
Species Recovery and Research.” San Francisco Estuary and
Watershed Science. Volume 16 (Issue 3). 15 pp. [Journal.] Viewed
online at: https://doi.org/10.15447/sfews.2018v16iss3art3.
Accessed: Feb. 8, 2024.
Rasmussen NL, Conrad JL, Green H, Khanna S, Wright H, Hoffmann K, Caudill
J, Gilbert P. 2022. “Efficacy and Fate of Fluridone Applications for
Control of Invasive Submersed Aquatic Vegetation in the Estuarine
Environment of the Sacramento-San Joaquin Delta.” Estuaries and
Coasts. Volume 45: Pages 1,842–1,860. [Journal.] Viewed online at:
https://doi.org/10.1007/s12237-022-01079-5. Accessed: Feb 15, 2024.
Ray PA, Wi S, Schwarz AM, Correa M, He M, Brown C. 2020. “Vulnerability
and risk: climate change and water supply from California’s Central
Valley water system.” Climatic Change. Volume 161 (Issue 11):
Pages 177–199. [Journal.] Viewed online at: https://link.springer.com/
article/10.1007/s10584-020-02655-z. Accessed Aug. 14, 2023.
Chapter 8. References
California Department of Water Resources 8-3
“The Atmospheric Rivers Program.” 2023. AcrGIS StoryMaps. Redlands (CA).
[Website.] Viewed online at: https://storymaps.arcgis.com/stories/
109b3b7524034628918be55282ab578f. Accessed: Feb. 21, 2024.
Vicuna S, Maurer EP, Joyce B, Dracup JA, Purkey D. 2007. “The Sensitivity of
California Water Resources to Climate Change Scenarios.” Journal of
the American Water Resources Association. Volume 43 (Issue 2):
Pages 482–498. [Journal.] Viewed online at: https://doi.org/
10.1111/j.1752-1688.2007.00038.x. Accessed Aug. 22, 2023.
State Water Project Long-Term Drought Plan
8-4 California Department of Water Resources
Chapter 9. Useful Web Links
California Department of Water Resources 9-1
Chapter 9. Useful Web Links
California Department of Water Resources Bulletin 120 Forecasts
https://cdec.water.ca.gov/reportapp/javareports
California’s Water Supply Strategy, Adapting to a Hotter, Drier Future
https://resources.ca.gov/-/media/CNRA-Website/Files/Initiatives/Water-
Resilience/CA-Water-Supply-Strategy.pdf
Center for Western Weather and Water Extremes
Subseasonal to Seasonal (S2S) Experimental Forecasts
https://cw3e.ucsd.edu/s2s_forecasts/
Delta Conveyance Project
https://water.ca.gov/deltaconveyance
Delta Conveyance Project
Adapting to Climate Change: Catching and Moving Water from Big Storms
https://water.ca.gov/-/media/DWR-Website/Web-Pages/Programs/Delta-
Conveyance/Public-Information/DCP_Diversions_Final.pdf
Delta Conveyance Project Environmental Impact Report
https://www.deltaconveyanceproject.com/planning-processes/california-
environmental-quality-act/final-eir/final-eir-document
Delta Harmful Algal Bloom Monitoring Strategy
https://deltacouncil.ca.gov/pdf/science-program/information-sheets/2022-
10-21-draft-delta-harmful-algal-bloom-monitoring-strategy.pdf
Delta Smelt Resiliency Strategy
https://resources.ca.gov/CNRALegacyFiles/docs/Delta-Smelt-Resiliency-
Strategy-FINAL070816.pdf
Drought Toolkit
www.usbr.gov/mp/bdo/docs/droughttoolkit-latest.pdf
State Water Project Long-Term Drought Plan
9-2 California Department of Water Resources
Healthy Rivers and Landscapes Program
https://resources.ca.gov/Initiatives/Voluntary-Agreements-Page
Sacramento Valley Salmon Resiliency Strategy
https://resources.ca.gov/CNRALegacyFiles/docs/Salmon-Resiliency-
Strategy.pdf
S2S Coalition
https://www.s2sforecasting.org/
