Recommendations for an Effective Water Rights Response to Climate Change

Note: If you haven’t yet heard about a climate change report prepared by the staff of the State Water Resources Control Board you will. This statement in Section Two “A water right is legal permission” on page 5 has been called particularly chilling. Note to the note: transferring a PDF format to a text format compatible with this website isn’t exactly exact. The graphs and other images didn’t reproduce and some of the layout is a bit different. We’ve put a great deal of effort to stay true to the wording.

STAFF REPORT

Recommendations for an Effective Water Rights Response to Climate Change
Identification of Data Needs and Recommendations to Incorporate Climate Change
into Water Rights Permitting Policies, Procedures, and Methodologies

February 2021
Division of Water Rights
State Water Resources Control Board
California Environmental Protection Agency

State of California
Gavin Newsom, Governor
California Environmental Protection Agency
Jared Blumenfeld, Secretary
State Water Resources Control Board
1001 I Street
Sacramento CA 95814
http://www.waterboards.ca.gov
E. Joaquin Esquivel, Chair
Dorene D’Adamo, Vice Chair
Tam M. Doduc, Board Member
Laurel Firestone, Board Member
Sean Maguire, Board Member
Eileen Sobeck, Executive Director
Division of Water Rights
Erik Ekdahl, Deputy Director
Prepared By:
Jelena Hartman, Senior Environmental Scientist (Specialist)
Jimmy Steele, Water Resources Control Engineer
Scott Frazier, Senior Environmental Scientist
Amanda Montgomery, Environmental Program Manager
Acknowledgments
Michael Anderson (California State Climatologist), Wyatt Arnold, David Arrate and Romain
Maendly (Department of Water Resources), Nell Green Nylen (Center for Law, Energy &
the Environment at UC Berkeley), John Callaway, Louise Conrad and Andrew Schwarz
(Delta Stewardship Council) reviewed and contributed to various sections of the report.

Table of Contents
Table of Contents ………………………………………………………………………………………………………. 2
Executive Summary ……………………………………………………………………………………………………. 3
1

Introduction …………………………………………………………………………………………………………. 4

Water Rights Overview …………………………………………………………………………………………. 5
2.1

Water Rights Permitting …………………………………………………………………………………… 6

Permitting Water Availability Analysis ……………………………………………………………………… 7
3.1

Supply: Unimpaired Flow …………………………………………………………………………………. 7

3.2

Demand: Senior Water Diversions …………………………………………………………………. 8

3.3

Demand: Instream Needs and Cumulative Impacts …………………………………………….. 9

3.4

Yield Analysis ………………………………………………………………………………………………. 10

Climate Change and California’s Water …………………………………………………………………. 11
4.1

Temperature ………………………………………………………………………………………………… 12

4.2

Precipitation …………………………………………………………………………………………………. 13

4.3

Snowpack ……………………………………………………………………………………………………. 13

4.4

Timing and Nature of Runoff ………………………………………………………………………….. 14

4.5

Fish and Wildlife Habitat ………………………………………………………………………………… 15

Select Models and Data for California ……………………………………………………………………. 16
5.1

Resources for Groundwater Sustainability and Flood Management ……………………… 16

5.2

California’s Fourth Climate Change Assessment ………………………………………………. 18

5.3

Estimating Impacts on a Finer Scale ……………………………………………………………….. 18

Challenges and Opportunities in Managing for the Future ………………………………………… 19
6.1

Long-Term Shifts in Hydrologic Trends ……………………………………………………………. 19

6.2

Changing Runoff Patterns ……………………………………………………………………………… 21

6.3

Amplified Hydrologic Extremes ……………………………………………………………………….. 22

Recommendations………………………………………………………………………………………………. 24

References ………………………………………………………………………………………………………… 28

This report and associated resources are available on the State Water Board’s webpage:
https://www.waterboards.ca.gov/waterrights/water_issues/programs/climate_change/

Executive Summary
This report identifies data needs, opportunities, and potential approaches for an effective water rights response to climate change. California’s climate is changing rapidly, and historic data are no longer a reliable guide to future conditions. Regarding changes projected for California, the uncertainty lies only in the magnitude of warming, but not in whether warming will occur.

Models indicate that due to warming alone, California will see less of its precipitation fall as
snow, which will result in diminished mountain snow pack, less snow in lower and intermediate elevations, and less “natural water storage” in the form of snow. The wet season is projected to become wetter, and the dry season will become longer and drier.
Anyone planning to take water from a lake, river, stream, or creek for a beneficial use requires a water right of some type. California law requires that every application to appropriate surface water demonstrate a reasonable likelihood that unappropriated water is available to supply the applicant. Hence, parties interested in obtaining an appropriative water right must conduct a permitting water availability analysis as part of the permitting process. Generally, water availability for permitting is calculated by estimating the amount of unimpaired flow in a stream during the diversion season, and subtracting the demand of all senior diversions and the demand for instream needs.

Permitting water availability analyses are typically based on historical data sets. However,
historical precipitation and streamflow records for the majority of the watersheds in California may not be sufficiently long to capture the full range of hydrologic variability needed to evaluate future available water supply. In addition, rising temperatures and changing precipitation patterns will affect hydrology, making future water availability increasingly difficult to reliably estimate.

Staff recommendations in this report offer a menu of options to make water rights permitting analysis more robust, and to support applicants in developing projects that will remain feasible in the future. The report concludes with a set of recommendations, which include actions to:
Leverage existing climate change data in permitting water availability analyses
Develop adaptive permit terms in new permits
Implement tiered requirements for climate change analysis in permitting, with complexity
based on categories such as size, location and/or project type
Develop a fact sheet for water right applicants to incorporate climate change
Strengthen the minimum period of record requirement for streamflow data
Require more rigorous analytical methods to estimate supply when gage data are not
available
Expand existing network of stream and precipitation gages
Reevaluate the existing instream flow metrics and criteria
Revise the Fully Appropriated Stream list
Prepare for and capitalize on capturing flood flows and storing them underground
Plan for droughts
Coordinate with other agencies and partners

1 Introduction
California is already experiencing the impacts of climate change, which will continue and
increase over the coming decades. Current and future impacts include increasing frequency
and intensity of extreme weather events, prolonged fire seasons with larger fires, increased
tree mortality, heat waves, rising sea level, and storm surges. Among changes in hydrology
are declining snowpack, with more precipitation falling as rain than snow, earlier snow melt, changes in the timing and volume of peak runoff, more frequent and more severe flooding, more frequent and longer droughts, and consequent impacts on water quality and water availability (Moser et al 2012, Pierce et al. 2018).

The State has taken bold action to limit the effects of climate change by enacting policies and programs to reduce emissions of greenhouse gases, both in California and in partnership with other states and countries. However, even with the most successful efforts to reduce greenhouse gas emissions, some amount of change is inevitable. Facing the threat of greater scarcity of water supplies, increased water demand, and limited water supply reliability, the State has increased focus on actions to build resilience and meet California’s water needs through the 21st century.

The State Water Resources Control Board (State Water Board) has taken a variety of actions to respond to climate change. Examples include funding the expansion of recycled water to increase drought resilience, adopting regulations to increase the collection of urban storm water, and reducing flood risk and enhancing water supply. Some of the actions that increase resilience of water supply and of ecosystems, such as water conservation and efficiency, and recycled water use, also have the potential to reduce greenhouse gas emissions through replacement of existing or future water supply sources that have higher carbon footprints (Sokolow et al. 2016).

Recognizing that the implications to California’s water resources due to climate change are
significant, the State Water Board adopted Resolution No. 2017-0012 “Comprehensive
Response to Climate Change” (State Water Board 2017b). The resolution provides direction
to staff to embed climate change consideration into all programs and activities, including the need to evaluate and make recommendations on regulatory and policy changes regarding the use of models to account for projected impacts of climate change when conducting water rights water availability analyses.

The Administration’s 2020 Water Resilience Portfolio outlines a vision of water management to support long-term water resilience and ecosystem health, and to build climate adaptability that works for people, the environment, and the economy. Among the suite of recommendations to strengthen regional preparedness are planning for a range of climate and growth scenarios, and incorporating climate change forecasts into permitting processes.

This report embraces and complements the vision of a resilient water system in the face of
changing climate, and presents staff recommendations to make permitting water availability analysis more robust, and actions that could support an effective response to climate change within the existing water rights framework in California. The report provides an overview of California’s system of water rights, and general principles of water availability analysis

for water right permitting. The report then summarizes existing information on projected climate change impacts on California’s water resources, and discusses potential challenges and opportunities that climate change poses for administering the water rights system. Finally, the report identifies a range of approaches to respond, individually or in combination, to climate change, including how existing information and available data can inform water rights permitting processes, and aid applicants in selecting appropriate season, rate, and quantity of proposed diversions. The list of staff recommendations in not exhaustive, and stakeholders may propose other options not listed in this report.

2 Water Rights Overview
In California, the State Water Board administers water rights law that is intended to ensure that surface water resources are put to the fullest extent to which they are capable in the interest of the people and for public welfare, that waste and unreasonable use of the water be prevented, and that water is conserved. Within the State Water Board, the Division of Water Rights manages day-to-day matters, including permitting, development of criteria for instream flow metrics, tracking water availability in stream systems, enforcement of the water right priority system, and protection of public trust resources including fisheries and water quality standards.

A water right is legal permission to divert and use a reasonable amount of water, which must be put to a beneficial use. Anyone planning to take water from a lake, river, stream, creek, or a subterranean stream requires a water right of some type. In water rights, “beneficial use” refers to the useful purpose to which water is applied. Common beneficial uses include domestic, irrigation, power generation, municipal, and industrial uses. Groundwater recharge is not a beneficial use of water on its own, but rather is one method of storing water.

Water rights in California are based on a priority system that is used to determine who can
continue taking water when there is not enough water to supply all needs. The priority status of a water right is particularly important during a drought, when some water right holders may be required to stop diverting water according to the priority of their water right. Suspension of right to withdraw water when there is not sufficient water in the system is implemented through curtailments.

The two major kinds of surface water rights in California are riparian rights, which generally
come with land bordering a water source, and appropriative rights. A riparian right is usually based on ownership of land bordering a lake, river, stream, or creek, and generally has a higher priority than appropriative rights. Riparian owners may use natural flows directly for beneficial purposes on riparian land and generally report their claimed use by filing of a statement; however, riparian right holders cannot store water during a wet time for use during a drier time. In general, riparian rights are of equal priority to other riparian rights, and must share available supplies among themselves during times of water shortage.

An appropriative right allows water diversion for use on either non-riparian or riparian land, and carries a priority in relation to other appropriative rights. Appropriative rights are based on a “first in time, first in right” approach. This means the user is entitled to the full quantity of water specified under the right before junior appropriators may exercise their rights. Since 1914, the State Water Board (or its predecessor) has been the exclusive agency for establishing an appropriative water right, with priority of right based on the date an application form is filed.

Water Rights Permitting

Any person or entity that seeks to divert and beneficially use a reasonable amount of surface water may file an application to divert and use water by permit. A water right permit is an authorization to develop a water diversion and use project; it specifies the quantity, a rate of diversion, season of diversion, where, and how water will be taken and used, and other conditions such as terms to protect instream flows. While a permit authorizes a water diversion project, the right to use water is obtained through actual use within the limits described in the permit. The water right license is a vested right that confirms actual diversion and use after a permitted project was constructed, and water was beneficially used in compliance with all conditions in the permit.

Developing an application is one of the key steps for a party interested in seeking a water right, and it is critical that appropriate season, rate, and quantity of proposed diversions are requested at the time of application. Once a party has submitted a water right application, the proposed season of diversion, rate, and quantity requested may not be increased (Cal. Code Regs, tit. 23, section 699).

In deciding whether to issue permits, the State Water Board considers the features and needs of the proposed project, all existing and pending rights, and instream needs to determine whether water is available for appropriation. The State Water Board must make a finding that there is unappropriated water to supply the applicant. This finding is made by relying on the water availability analysis and other information developed during application processing.
Notably, there are cases when applications are not accepted or permits are denied:

·The State Water Board will not issue a water right permit if the proposed project is not in
the public interest, or if the proposed project unreasonably harms fish, wildlife, the
environment, or water quality.

· The State Water Board is precluded from accepting applications for new water rights in
a stream system designated as fully appropriated, unless the designation allows new
applications under specified conditions. Fully appropriated stream (FAS) systems are
those where there is insufficient supply for new water right applications. Streams can
be fully appropriated seasonally or all year. The State Water Board has adopted a
formal FAS Declaration that defines the critical reaches of each fully appropriated
stream system, including the seasons in which water is unavailable for appropriation
(State Water Board 1998).

· The State Water Board will not issue a permit for a water right unless there is water
available for appropriation. Even if a stream is not on the Fully Appropriated Streams
List, water may not be available for appropriation. California law requires that every
application for a water right permit set forth sufficient information to demonstrate a
reasonable likelihood that “unappropriated” (unclaimed) water is available to supply the
applicant (Water Code, section 1260 (k)). The complexity of the initial showing depends
on project specifics, such as project size, instream resources of the source stream,
amount requested compared to estimated supply, and existing impairment in the
watershed. An applicant generally conducts a more detailed permitting water
availability analysis during application processing. That detailed analysis usually considers the water needs of both instream uses, such as fisheries and recreation
(Water Code, section 1243), and senior right holders.

According to the State Water Board’s Electronic Water Rights Information Management
System (eWRIMS), there are currently 349 pending applications for appropriative water rights, excluding a subset called “state filed applications”.
The total combined face value of the 349 pending applications is 11.2 million acre-feet
annually. While a significant amount is being requested for future appropriation, the vast
majority of requested water by volume comes from just a few applications. In total, 16 percent of the pending applications account for 99.8 percent of the requested water volume. Most water right applications are for relatively small amounts of water. The distribution of pending water right applications by size is an important consideration as the State Water Board moves forward in its efforts to incorporate climate change into water rights permitting process.
Table 1. Pending Appropriative Water Right Applications (September 2020)
Application Face
Value (acre-feet
per year)
< 1,000
≥1,000
Total

Number of
Applications
293
56
349

Combined Face
Value (acre-feet per
year)
27,626
11,212,681
11,240,306

Percent of Total Volume
Applied For (all pending
applications)
0.2%
99.8%
100%

3 Permitting Water Availability Analysis
Permitting water availability analyses generally are comprised of two major steps: estimating unimpaired flow, and accounting for demands for senior diverters and instream needs. The State Water Board determines the sufficiency of water availability analysis and technical approach on a project-specific basis. While there are no statewide guidelines or established requirements for each step, the analysis must include multiple locations (i.e., points of interest) along the flow path between a proposed project and the downstream limit of the analysis (such as a bay or ocean). Complicated watersheds may require hydrologic modeling to determine whether water is available for appropriation. For example, in the Sacramento-San Joaquin River Delta (Delta) watershed, a
robust hydrologic modeling tool may be necessary to estimate flows, exports, reservoir
storage, deliveries, and other parameters to properly evaluate flow-availability relationships.
3.1

Supply: Unimpaired Flow

The first part of the analysis is to estimate the unimpaired flow, i.e. the amount of water that would flow down a stream if there were no diversions in the watershed. Applicants may use a number of methods to estimate the amount of unimpaired flow at proposed points of diversion, and other locations downstream. Typically, these methods rely on historical stream gage and precipitation data, which can be available on a daily, monthly, or a seasonal time step. While

permitting water availability analyses often use all years of an available record, there is no set requirement for the length of record considered sufficient for a rigorous water availability analysis. The exception is the region covered by the Policy for Maintaining Instream Flows in Northern California Coastal Streams (i.e., North Coast Instream Flows Policy), where a water availability analysis must include at least ten water years of complete record of daily streamflows (State Water Board 2014a).

The current preferred method to estimate supply uses stream gage data. Often, in a gaged
stream system, the gage is not at the exact location of a proposed project. For example, a
projects may be in the upper watershed, draining into a gaged location. Practitioners
commonly use the adjustment of stream records method, which estimates streamflow for a site of interest by adjusting stream gage data from an alternative, typically downstream, location. The alternative site’s gage data are typically adjusted to account for differences in drainage area and precipitation at the point of diversion compared to the gage location (State Water Board 2002).

However, fewer than 15 percent of the state’s significant stream segments are well gaged (The Nature Conservancy 2018). When gage data are unavailable for a stream system, applicants can use modeling to estimate supply. Two commonly used methods to estimate average seasonal unimpaired flow in a stream system that is not gaged include:

3.2

· Reference stream gage with adjustment of streamflow records. This method transfers
streamflow properties from a nearby reference gage to an ungaged site with similar
watershed characteristics. The water right applicant must provide sufficient justification
for the reference gage selection. Reference gage streamflow data are adjusted to
account for differences in drainage area and precipitation at the reference site and the
site of interest to generate a representative hydrograph (State Water Board 2002).

· Precipitation-based streamflow models. This approach, also known as rainfall-runoff
models (Sitterson et al. 2017), uses precipitation data and watershed characteristics
(relief, soil saturation, vegetal cover, and surface storage) to estimate runoff (i.e.,
streamflow) for a particular watershed area. This method is rarely used but may be
appropriate if a paired reference stream gage cannot be identified. It could also be
appropriate if the watershed has a robust methodology in place for unimpaired flow,
such as estimates generated by California Department of Water Resources (2016).

Demand: Senior Water Diversions

The second part of the permitting water availability analysis is to estimate the existing water emand on an applicant’s proposed water source. To determine whether the proposed
diversion would impact senior diverters downstream, applicants must evaluate the cumulative demand of all senior diversions (both right holders, and pending water rights along the flow path between the proposed project and the downstream limit of the analysis) against unimpaired flow estimates.

Applicants rely on data in the Electronic Water Right Information System (eWRIMS) to assess senior water demand. The eWRIMS database compiles water rights information in California, such as face-value (the maximum amount of water authorized for diversion) and use information for permits, licenses, registrations, and other authorized diversions, and the annual

reports of actual diversion and use by all water right holders. Water demand data in eWRIMS have limitations which may affect the accuracy of the analysis. Some of the limitations involve reporting errors, data quality, and accounting for water diversions reported under multiple rights such as claimed overlapping rights (State Water Board 2015b).

Measurement and reporting regulation adopted by the State Water Board in 2016 (State Water Board 2016b) may, over time, improve some of the data issues related to actual water diversion and use by setting requirements related to monitoring frequency, accuracy of measurement devices, and annual reporting. The measurement requirements apply to all
water rights that divert more than ten acre-feet of water per year, and the annual reporting
requirements apply to all diversions. However, the eWRIMS data system lacks modern tools
that would help prevent submission of inaccurate or poor-quality data. Substantial
improvements or replacement of the system would be needed to ensure submission of
accurate and high-quality data.
Text Box 2: Water Supply Report
Water right applicants within the geographic scope of the Policy for Maintaining Instream Flows in Northern California Coastal Streams must complete an analysis called a Water Supply Report (State Water Board 2014a). The Water Supply Report must include a set of flow frequency analyses, and quantify the amount of unappropriated water supply remaining instream after senior rights are accounted for to determine if sufficient amount of water is likely available to the proposed project. Daily data from a streamflow gage with at least ten years of record are required for the analysis, and the demand and season of all senior water right applicants, holders, and claimants must be accounted for. The Water Supply Report approach is not required in areas outside of the North Coast Policy area, although the methodology is typically provided as guidance for projects in other parts of California. The Water Supply report may not be an appropriate approach in complicated watersheds where watershed specific modeling may be needed (such as the Bay Delta watershed).
3.3

Demand: Instream Needs and Cumulative Impacts

Consideration of instream needs is a critical component in the development of a permitting
water availability analysis. The State Water Board is required to take into account, whenever it is in the public interest, the amount of water required for recreation and preservation of fish and wildlife resources. Even if an applicant can demonstrate that there is unappropriated water after accounting for senior diversions, that water may not be available for appropriation if the proposed diversion could impact fish and other aquatic and riparian species. During water availability analysis, cumulative impacts are typically assessed at the project location and at various locations downstream. The results of these assessments often lead to terms and conditions in a water right permit that limit the timing, rate, and amount of diversion for the protection of the hydrograph and instream resources. For example, terms can set minimum bypass flows before water can be diverted, restrict the diversion season, and/or preserve portions of peak flows needed for channel maintenance. Water may not be available for appropriation in cases where the proposed project, in combination with senior diversions, significantly affects instream flows and/or affects aquatic and riparian species.

Only limited areas of California have a set of site-specific instream flow standards for the
protection of instream beneficial uses. As a consequence, most watersheds in California have no established metrics that the cumulative impacts of diversions can be measured against. In the absence of site- or watershed-specific flow standards, parties pursuing projects may review if other permitting projects in their stream system have developed information that may be adapted to their project. Otherwise, parties need to develop site-specific information for their project. Developing site-specific criteria may involve consultation with fisheries agencies, modeling and/or field study, and results in a customized approach to criteria and testing of the criteria in an assessment of cumulative impacts.
Text Box 3: Instream Flow Standards
Water right applicants in areas covered by the Policy for Maintaining Instream Flows in
Northern California Coastal Streams (North Coast Instream Flow Policy) generally complete a Cumulative Diversion Analysis as part of their application. The Cumulative Diversion Analysis evaluates the effects of a proposed project, in combination with existing diversions, on instream flows needed for protection of anadromous fish. Three criteria restrict the timing and amount of flow diverted by limiting the season of diversion, establishing minimum bypass flows, and limiting the maximum cumulative rate of diversion from a watershed. Water right applicants are able to use regional protective instream flow criteria, or may choose to develop site-specific criteria to evaluate whether a proposed project, in combination with senior diversions, adversely affects instream flows needed for the protection of fishery resources.

Regional criteria provide an avenue for quicker processing of applications, without the need to conduct costly site-specific fishery studies. The regionally protective season of diversion runs from December 15 through March 31, restricting new diversions to the period of highest winter flows when impacts of water withdrawals are minimized. Regionally protective minimum bypass criterion sets the minimum instantaneous flow rate that must be moving past the point of diversion before water may be diverted. The regionally protective maximum cumulative diversion criterion limits cumulative rate of all diversions in a watershed in order to preserve natural flow variability and effective channel maintenance flows to meet the habitat needs of anadromous salmonids. In other words, water may only be extracted once instream flows exceed the minimum bypass flow, and only up to the point when the sum of the rates of diversion for diverters within a watershed reaches the maximum cumulative diversion criterion (5 percent of the 1.5-year instantaneous peak flow).
In another example, diversions associated with cannabis cultivation operations are only
permitted when sufficient instream flows are available. To evaluate if water is available,
cannabis cultivators must comply with either existing instream flow requirements, or the
Tessmann instream flow requirements, whichever is greater (State Water Board 2017a). In
general, during the wet season, the Tessmann Method compares 40 percent of the mean
monthly natural flow to 40 percent of the mean annual flow; the resulting instream flow
requirement for any given month is the greater of the two.
3.4

Yield Analysis

As a final step, parties may conduct a yield analysis to project how much water will be
available to supply their project, after accounting for senior diverter and instream needs at the

point of diversion and along the flow path. Year to year flow tends be highly variable on many streams due to California’s Mediterranean climate, especially streams that are rain fed. For example, for a project with a small source watershed or where there is significant downstream demand, there may be enough flow to fully supply the project in a wet year, but only enough flow to provide a fraction of the anticipated demand during drier years. Typically, a project will test a range of water years, either by using all gage years available or a selection of years including dry periods to calculate project yields and the number of days available for diversion.

4 Climate Change and California’s Water
California’s Mediterranean climate is characterized by cool moist winters and hot dry summers. In addition to being strongly seasonal, California spans multiple climate zones, from temperate rainforests of the Pacific Northwest to arid deserts of the Southwest (Hanak et al. 2011). Thisgeographic and climatic diversity results in regional hydrological variability throughout the state, with a stark climatic gradient from the cool coastal areas to hot inland areas, and big climatic differences between the Central Valley and the Sierra Nevada. Additionally, California has the greatest year-to-year precipitation fluctuations compared to anywhere else in the United States, with annual precipitation totals ranging from as little as 50 percent to more than 200 percent of long-term averages (Dettinger 2016).
Typically, a few strong storms (atmospheric rivers) during the winter provide 30 to 50 percent of California’s annual precipitation and 40 percent of Sierra snowpack. With warmer air, and changing ocean conditions, atmospheric river episodes have the potential to increase in duration and intensity yielding increases in precipitation from the largest storms (Dettinger, 2016, Gershunov et al. 2019). There is also a growing body of evidence that persistence of anomalously high atmospheric pressure can deflect atmospheric rivers, significantly diminishing California water supplies (Swain et al. 2016). Furthermore, paleoclimatic evidence from tree rings, buried stumps, and lakebed sediment cores suggests decadal or longer-scale climate fluctuations, and reveals greater variability than captured in the instrumental record, particularly in the form of severe and prolonged droughts (California Department of Water Resources 2015a). Even changes beyond the State’s borders have a strong influence of California’s water supply, as Southern California receives approximately one-third of its water supplies from the Colorado River (Hanak et al. 2018).
Because California contains multiple climate zones, each region of the state is experiencing a combination of impacts from climate change unique to that area. While significant
uncertainties still remain for long-term local precipitation and temperature changes, projections at the regional and statewide levels are already available, and suggest a continuing warming trend, greater precipitation volatility, earlier snowmelt, shifting of the timing and nature of runoff, increased frequency of droughts and flooding, and sea level rise affecting coastal and Delta water quality.
The California Fourth Climate Change Assessment, completed in 2018, confirmed the
consensus of the climate change science community that the global climate and California’s
climate are changing rapidly, and that past is no longer a reliable guide to future conditions.
Studies from the Fourth Climate Change Assessment additionally suggest that extreme events will occur more frequently in California due to climate change. For example, with warmer air,

and changing ocean conditions, atmospheric river events have the potential to increase in
duration and intensity yielding increases in precipitation from the largest storms (Moser et al.
2012). Conversely, a number of studies suggest that California should prepare for more
frequent, more severe, and longer-lasting droughts (He et al. 2018).
Text Box 4: Projecting Climate Impacts
Climate models and sets of future scenarios used to project climate are continuously being
updated, as different modelling groups around the world incorporate higher spatial resolution, new physical processes and biogeochemical cycles, and employ scenarios rooted in socioeconomic trajectories (Editorial 2019). This report provides basic information on the
general climate change traits relevant to administering water rights in California; readers are directed to other sources for the latest in the climate change science.
Climate models are a source of uncertainty in climate projections. Projections of future climate conditions are derived from global climate models (GCMs). Climate models use mathematical equations that are used to make weather forecasts but are run over much longer time horizons and represent physical processes in the atmosphere, oceans, land surface, and ice. And while climate models perform well in resolving climate variables as statistical weather information, they are not designed to resolve actual weather conditions.

Climate models vary in spatial and temporal detail that they provide, as well as how well each is capable of simulating the natural variability that has been observed in different regions.
One of the largest uncertainties in predicting future climate is the course the society chooses in terms of energy and land use, resulting in different greenhouse gas emissions pathways. Scientists use a range of plausible future global greenhouse gas emission scenarios, land use, population growth, technology, economic activity, and other factors to model future climate.
These scenarios are called Representative Concentration Pathways (RCPs). For example,
RCP8.5 represents a high emissions scenario, also known as the “business as usual”
scenario, whereas RCP4.5 represents a medium emissions scenario where societies attempt
to reduce greenhouse gas emissions.
In general, climate models perform best for variables that are strongly dependent on
temperature. For example, for California, the uncertainty lies only in the magnitude of
warming, but not in whether warming will occur. While there is substantial uncertainty in the amount of precipitation change over California over the next few decades, the definitive
likelihood of continued warming overcomes that precipitation uncertainty to create an
unambiguous trend towards diminished snowpack and earlier snowmelt timing (Climate-Safe Infrastructure Working Group 2018).
4.1

Temperature

Statewide annual average air temperatures have generally risen since 1895, with temperatures increasing at a faster rate starting in the 1980s (Office of Environmental Health Hazard Assessment; OEHHA 2018). The four years from 2014 to 2017 were especially warm, with 2014 being the warmest on record. Furthermore, annual average temperatures in California are projected to rise significantly (5.0 to 8.5 °F by the end of the century), with extremely warm years and heat waves occurring more frequently (Moser et al. 2012). Interior regions in California are expected to experience greater warming than coastal areas (Pierce et al. 2018).

Projected temperature increases will affect California’s hydrology, with further effects felt by the state’s water supply, hydroelectric power supply, agriculture, recreation, and ecosystems (Cayan et al. 2006). Due to warming alone, California will see less of its precipitation fall as snow, which will result in diminished mountain snow pack, and less natural water storage in the form of snow. Warmer air temperatures will change precipitation and runoff patterns, affecting freshwater supply availability, and increase the risk of severe weather events such as heat waves and intense storms (OEHHA 2018). Warming also has important implications for aquatic ecosystems, particularly for fisheries where increased water temperature can affect survival and reproduction.
4.2

Precipitation

Records indicate that year-to-year variation in the annual precipitation in California has
intensified over the past century, with more distinct dry and wet periods, although the overall annual precipitation accumulation trend shows little change. Climate change modeling suggests that California will continue to experience the seasonal pattern of dry summers and wet winters, as well as interannual and decadal variability marked by greater precipitation extremes (Moser et al 2012). However, there is no agreement among models on the projected trends in statewide annual precipitation.
Whether the statewide amount of precipitation is projected to increase or decrease largely
depends on whether models place the regional analysis more in the northern or southern
regime of large-scale change (Berg and Hall 2015). Most climate models project drier
conditions in Southern California, with heavier and warmer winter precipitation in Northern
California.
Additionally, seasonal changes are projected to become more pronounced. Recent research
suggests that December through February will remain wet or become even slightly wetter, but shoulder spring and fall seasons will become drier (Pierce et al. 2018). In other words, the wet season will bring wetter conditions during a shorter period, whereas the dry season will become longer and drier (Gershunov et al. 2019). A longer dry season would heighten some important climate impacts including fire risk, water and energy demand, and ecosystem stress.
4.3

Snowpack

California’s Sierra Nevada snowpack is a critical hydrologic resource, providing more than
60 percent of the water used by communities, agriculture, and industry across the state (Reich et al. 2018). Snowmelt currently supplies an annual average of 15 million acre-feet of water, which is gradually released in spring and summer (OEHHA 2018). Water stored in the snowpack also plays a vital role for the ecosystems, supplying cold water habitat for salmonids and water for forests. In recent decades, there has been a trend toward more precipitation falling as rain than snow.
By the end of the century, the Sierra snowpack may shrink to half of the historical range,
resulting in reduced natural water storage (Reich et al. 2018). California’s Fourth Climate
Change Assessment indicates that the decline in spring snowpack will occur even if the
amount of precipitation remains stable (Bedsworth et al. 2018). Warming conditions will
continue the trend of less precipitation falling as snow, and snowmelt occurring earlier in the

spring (Pierce et al. 2018) with higher elevation watersheds seeing more change in
precipitation patterns. For example, the San Joaquin watersheds located in higher elevations are projected to have the largest percentage increase in flood volumes because of precipitation falling more as rain instead of snow (Figure 1, California Department of Water Resources 2017). The projected decreases in snowpack will have profound effects on the availability of water for downstream storage, reservoir operations, direct diversions, flood management, and ecosystems.
Figure 1. Projected Impacts on Central Valley Precipitation Patterns (California
Department of Water Resources 2017).

4.4

Timing and Nature of Runoff

The arrival of warmer temperatures earlier in the year causes snowmelt earlier in the year, with less spring and summer snowmelt. In addition, warming causes a greater share of
precipitation to fall as rain which also affects the timing of runoff (Reich et al. 2018).
In the Sacramento River system, the peak of the average monthly runoff has shifted earlier by nearly a month between 1906-1955 and 1956-2007 (California Department of Water
Resources 2015a). Additionally, the fraction of snowmelt runoff entering the Sacramento River between April and July relative to total year-round water runoff has declined over the past century (OEHHA 2018).
Watershed characteristics strongly influence the hydrological response to climate change. In higher elevation snow-fed watersheds, the timing of peak runoff is projected to move earlier in the year, with increasing flashy winter runoff while reducing spring and summer streamflow (Davenport et al. 2020). Streamflow projections for the Feather River on the Cal-Adapt streamflow tool illustrate changes to future unimpaired streamflow patterns by the end of the century (Figure 2). Climate models show peak streamflow occurring nearly two months earlier, accompanied by an increase in quantities of peak streamflow compared to the observed data.

Figure 2. Projected vs. observed monthly average unimpaired streamflow – Feather
River near Oroville (adapted from Cal-Adapt streamflow tool).

4.5

Fish and Wildlife Habitat

Recent research suggests that changing climate has magnified stress on California’s
freshwater ecosystems. For example, past land use changes, water management, fishing, and other stressors have contributed to the loss of freshwater habitat and diversity of native species in California. Limited diversity and habitat loss left salmonids with reduced capacity to cope with increasing temperature and diminishing snowpack (Herbold et al. 2018).
Warming trends have already been documented in California’s aquatic ecosystems for which long-term temperature data are available (Moyle et al. 2013). With warming temperatures, more precipitation falls as rain instead of snow, decreasing the quantity of snowmelt that supplies streams and rivers (OEHHA 2018). A decrease in the amount of snowmelt runoff affects ecosystems by reducing the amount of cold-water habitat that is available for native fish species such as salmonid fishes. Increases in water temperature and loss of cold-water flows can negatively affect migration, spawning, egg viability, and rearing conditions (OEHHA 2018).
Furthermore, changes in precipitation and runoff patterns will likely modify seasonal availability of spawning and rearing habitat for some native fish (e.g., Chinook salmon) and favor fishes that can persevere when stream flows are low and intermittent for extended periods (Moyle et al. 2013). The more the “natural” flow system in streams and rivers is modified, the less native fishes will be favored. Therefore, native fishes and native stream-dependent species will ecline as stream reaches dry up or become warmer (Moyle et al. 2013).
Shorter precipitation seasons, and persistence of high temperatures longer into the fall may
diminish natural flows to ecosystems, affecting water quality. Ecosystems exposed to rising
sea levels, such as the Delta, are especially vulnerable to decreases in tributary flows and
increasing salinity.

5 Select Models and Data for California
Thus far, California has invested in a considerable amount of research to understand how a
changing climate will affect water resources, and identify ways to build resilience, adapt, and prepare for impacts of climate change.
5.1

Resources for Groundwater Sustainability and Flood Management

California Department of Water Resources (DWR) plays an important role in planning and
managing much of California’s water resources, systems, and infrastructure. As a result, DWR is actively involved in climate change science to analyze and assess potential impacts to California’s water system, and develop adaptation responses (California Department of Water Resources 2018).
DWR developed climate change data, water operations modeling, and Delta hydrodynamic
modeling for use by the Water Storage Investment Program in 2016. With additional
refinements, DWR provides those climate change data, tools, and guidance material to support implementation of Sustainable Groundwater Management Act (SGMA). SGMA Climate Change Resources are in the public domain. The climatological data include historical detrended precipitation, and reference evapotranspiration along with change factors for projected climate conditions centered around 2030 and 2070. The climate projections for 2070 include three scenarios: a central tendency, and two extreme cenarios (i.e., one drier with extreme warming and one wetter with moderate warming). The hydrological data provide projected unimpaired stream inflows for major streams in the Central Valley, and streamflow change factors for areas outside of the Central Valley and smaller ungaged watersheds within the Central Valley. Applying change factors preserves historical interannual variability while the magnitude of events may be increased or decreased based on projected changes in precipitation and air temperature from global climate models.
DWR has also developed a comprehensive framework for system-wide management and flood risk reduction planning for the Sacramento and San Joaquin River Basins. The 2017 Central Valley Flood Protection Plan Update (Update) incorporated climate change into flood risk evaluations and planning. The 2022 Update will provide a wider range of potential climate change projections over a planning horizon that extends to 2072. The 2022 Update will also be supplemented by a pilot study in the Tuolumne River watershed, which will involve the development of methods and tools to support decision scaling, including climate-informed time series of simulated weather data (California Department of Water Resources 2020). Once available, these climate change resources may be used to inform other projects and planning efforts.
Text Box 5: Decision Scaling
To improve planning for the uncertain effects of climate change, DWR has used “decision
scaling” to systematically explore performance of the Central Valley water system over a range of temperature and precipitation changes (Schwarz et al. 2018, California Department of Water Resources 2019). The decision scaling approach allows for the assessment of sensitivity to a wide range of potential future climate conditions, the estimation of the probability of specific

outcomes, and the ability to plan for changes informed by the best available science, yet it is not reliant on a precise prediction of future values.
For example, the response surface (left panel in Figure 3) summarizes results of a twodimensional sensitivity analysis for one of the decision-relevant metrics under a range of warming and precipitation change. The current conditions estimate for average annual State Water Project deliveries is at 0°C change in temperature, and 0 percent change in
precipitation. Blue shades represent increasing average annual deliveries and orange shades represent decreasing deliveries. The black line shows that current performance level can be maintained at combinations of temperature and precipitation shifts.
A GCM-informed probability density function of climate projections for the year 2050 is
superimposed on the response surface, and shows probabilistic estimates of exposure (right panel in Figure 3). The 2050 climate probability density is centered around no change in precipitation, and 2°C change in temperature, at which average annual deliveries decline by approximately 20 percent with no adaptation strategies employed.
Figure 3. Figure 3. Average Annual State Water Project Deliveries sensitivity and
exposure to climate change (adapted from California Department of Water Resources 2019).

Another example of water management planning that uses the decision scaling method to
incorporate climatic uncertainty is research to support use of floodwaters for managed aquifer recharge (Flood-MAR) on agricultural lands, working landscapes, and managed natural landscapes. Flood-MAR is an integrated water management strategy that can provide flood risk reduction, aquifer replenishment, drought preparedness, ecosystem enhancement, and other potential benefits. DWR is currently conducting a pilot study in the Merced River Basin that will evaluate the potential for using flood waters to recharge groundwater, and demonstrate the use of the decision scaling to explore effectiveness of different adaptation strategies (California Department of Water Resources 2020).

5.2

California’s Fourth Climate Change Assessment

The State has undertaken four comprehensive climate change assessments, designed to
assess the impacts and risks from climate change. Completed in 2018, California’s Fourth
Climate Change Assessment included several projects to improve access and presentation of climate change information (Bedsworth et al. 2018). While the general direction and trends in the projections have remained consistent with previous assessments, analysis prepared for the Fourth Assessment further refined projections for California, and provided higher spatial resolution and improved treatment of climate extremes.
Recognizing the need to use multiple global climate models while reducing the number of
simulations, a subset of ten global climate models that closely simulate important aspects of California’s climate were identified for use in water resources planning (California Department of Water Resources 2015b). Among the ten, the State prioritized four global climate models for the California’s Fourth Climate Change Assessment (Pierce et al. 2018):
1.A warm/dry simulation (HadGEM2-ES)
2. A cooler/wetter simulation (CNRM-CM5)
3. An average simulation (CanESM2)
4. A simulation that is a complement, most unlike the first three for the best coverage of
different possibilities (MIROC5)

The climate simulations developed for the California’s Fourth Climate Assessment are in the
public domain and available from the Cal-Adapt online portal in raster or tabular formats. The data cover 1950-2005 for the historical period, and 2006-2100 for medium and high emissions scenarios. The data include daily temperature and precipitation over California at a resolution of about 3.7 miles. Additional variables for the subset of ten models are relative humidity, wind speed, and surface solar radiation. The Variable Infiltration Capacity (VIC) land surface model was used to estimate historical and future daily hydrologically relevant variables, such as snow cover, soil moisture, runoff, water loss from plants, surface moisture and heat fluxes (Pierce et al. 2018).
5.3

Estimating Impacts on a Finer Scale

Future climate change projections are variable due to uncertainties related to greenhouse gas emissions pathways and global climate models. Hydrologic modeling informed by long-term measurement data sets can constrain the functional uncertainty of global climate model-based future hydrology projections. For example, a mechanistic, process-based hydrologic model can give a more granular representation of watershed-level water balance that can be customized to site-specific data on topography, soils, and geology.

There are several hydrologic models that can incorporate the results of downscaled global
climate models to characterize the potential impacts of climate change on hydrology and water availability in a specific watershed. These hydrologic models include, but are not limited to, the Basin Characterization Model (BCM), Variable Infiltration Capacity (VIC) Model, Water Evaluation and Planning System (WEAP) Model, and the Hydrologic Modeling System (HECHMS).

Spatially explicit hydrologic models that quantify the water balance by comparing measured
streamflow with model output can be calibrated using a historical baseline. The regional
hydrological relationships between climate and landscape can then be applied to derive
potentially more detailed forecasts of future climate projections at a watershed or regionalscale (Flint et al. 2013). As a result, the historical climate data in combination with future climate scenarios can provide a comprehensive dataset of regional climatic and hydrologic trends, but is also spatially detailed enough to provide fine-scale examples of local hydrological impacts of climate change on the landscape (Thorne et al. 2012).

6 Challenges and Opportunities in Managing for the Future
Permitting water availability analyses are generally based on historical data to estimate
unimpaired flow, and to evaluate instream resource needs. As timing and amount of water
flows change, historical reliability of existing water rights will change (Schwarz 2015).
However, as past conditions are no longer a reliable guide to future conditions, permitting
water availability analyses should incorporate climate science and projections to account for
impacts of climate change. Climate change projections point to both long-term shifts in the
timing and magnitude of peak streamflows, and amplified hydrologic extremes, which will make
it increasingly difficult to reliably estimate availability based on the observed record.
Furthermore, implementation of curtailments may become more frequent, and additional
actions may be required to address impacts to water quality, and fish and wildlife. This section
aims to create connections by summarizing some of the key challenges and considering
opportunities to effectively respond to projected climate change when administering water
rights.
6.1

Long-Term Shifts in Hydrologic Trends

Estimates of unimpaired flow typically rely on historical data. However, due to the low number of gages and relatively short period of most precipitation and gage records, particularly on the smaller stream systems, there is often not enough information to characterize multi-year or decadal hydrologic variability, which significantly limits the ability to reliably estimate water availability.
The precipitation record for Sacramento offers one example of why it is important to
comprehensively characterize hydrological variability. Sacramento has one of the longest
instrumental rainfall records, which extends back to the 1850s. Year-to-year variability in
Sacramento rainfall is representative of California’s precipitation fluctuations, and ranges from just over 5 inches to more than 35 inches per year (Figure 4). The 30-year running average (a standard reporting interval for climate averages) also exhibits variability, suggesting there are decadal-scale fluctuations in average rainfall. The 30-year running average reveals an upward trend in annual precipitation from the 1920s to 2000 (California Department of Water Resources 2015a).

Figure 4. Annual Precipitation 1850-2014 in Sacramento, California (California Department
of Water Resources 2015a).

Many of California’s permitted and licensed water rights reflect water availability analyses
based on stream gage data from a relatively wet time period which likely does not capture
drying trends or long-term drought conditions. It will be difficult for existing water right holders to divert the volume of water permitted under their water right if climate conditions swing towards drier overall trends such as those observed from 1925-1955. Such a scenario may already be occurring within the Colorado River Basin, where a 20-year drying trend has resulted in cutbacks to deliveries that were originally based upon historically higher flows (USBR).
There are several options, applied on their own or together, that would help to better
characterize hydrological variability for estimating unimpaired flow in permitting water
availability analysis:
· Maintain the existing stream gaging network to ensure reliable data are available for
water rights administration, and support expanding the stream gaging network where
possible. A robust stream gage network and more complete hydrologic data will
support a more effective management of water resources.

· Strengthen analyses by expanding the minimum period of record supporting the
analyses. The additional streamflow data may help to better characterize wet and dry
trends, extremes, and natural hydrologic variability of the stream system.

· Update the current methodology used to adjust stream records based on alternative
gage locations by increasing the number of required alternative sites with stream gage
data. Updating this methodology will improve accuracy and to increase the range of
historical, climatic, and hydrologic variability captured in the analysis, and could

leverage efforts to integrate various surface water and groundwater models. Another
way to improve accuracy may be temporary installation of a portable stream gage(s) at
requested points of diversion to pair estimated values with quantified streamflow.

6.2

Examine reconstructed hydroclimate data to supplement gage records and get an
insight into a broader range of natural hydrologic variability. Because California’s
instrumental hydrologic record is relatively short, other sources of information can
provide critical context for understanding natural hydrologic variability (California
Department of Water Resources 2015a). This may include a variety of approaches,
such as examining available hydroclimate reconstructions based on tree-ring data, and
pairing with local observational data to develop longer precipitation and temperature
records that can be use with a hydrologic model to estimate streamflow. Hyrdoclimatic
Reconstructions for Northern and Southern California River Basins are in the public
domain.
Changing Runoff Patterns

The requested season, rate, and quantity of proposed diversions may not be increased once a water rights application is submitted. Shifting runoff patterns may affect water availability for many existing water rights holders. Many climate change projections for California indicate the timing of peak runoff will shift from observed historical patterns. Shifting runoff patterns (such as peaks during spring instead of summer) may eliminate or substantially limit an existing water right holder from maintaining traditional project yields. Parties facing this issue may need to seek a new water right as the season of diversion in an existing appropriative right may not be expanded. Water storage projects may need to reconfigure operations to capture peak flows when able, and to preserve carryover water to protect cold-water sensitive species needs as well as to preserve water quality in the Delta.
A common, readily available set of facts about water supply and use can make balancing
competing needs less contentious and more efficient. There are multiple actions and
resources that could aid incorporating climate change forecasts into permitting processes, and support effective water rights administration in the face of a changing patterns of runoff:
· The State Water Board has engaged in early efforts to incorporate climate change on
specific projects by encouraging applicants to include projected climate change in their
water availability analyses. Existing datasets and tools that are in the public domain
can help explore how climate change will affect hydrology. Climate change resources
developed by the State include projections developed for the California’s Fourth Climate
Change Assessment, and data and tools provided by DWR to support implementation
of SGMA.

· In order to support potential water right applicants in developing projects that will remain
feasible in the future, the State Water Board could develop a fact sheet to advise that
parties consider how climate change could affect water availability. Consideration of
several points would help applicants select appropriate season, rate, and quantity of
proposed diversions, to help improve the long-term feasibility of their water right. In
addition to conducting water availability analysis based on historic data, applicants
should evaluate water availability under a scenario that includes projected hydrology to

assess if the project would be viable in the event of continued shifts in conditions. For
instance, applicants may consider whether their application should focus on a season of
diversion with a shorter precipitation period or potentially greater rate of diversion during
higher peak flows. Future applicants may also need to evaluate proposed purpose of
use, as warming may shift plant growing seasons earlier in the year (USDA Climate
Hubs), with a possibility of exposure of buds to spring frosts earlier than the traditional
frost protection season.

6.3

· In order to continue to protect and preserve fish and wildlife habitat with changing
hydrology due to climate change, it may be necessary to modify existing instream flow
criteria and metrics required by the North Coast Instream Flows Policy for applications
and petitions on existing rights. This will likely require developing tools for identifying
functional ecosystem flows and further development of scientific literature that assesses
and plans for the hydrological impacts of climate change on anadromous fish species.
Where regional criteria or flow objectives are not available, the State Water Board may
need to consider whether existing flow conditions support aquatic beneficial uses, and
how flow may change under climate change projections.

· Among opportunities to leverage ongoing efforts is the work that the Delta Stewardship
Council is leading to devise approaches and conduct modeling and analyses to address
the priority management questions, assess vulnerabilities, and evaluate potential
adaptation options. While the work is specific to the Delta, the findings will have
significant repercussions for ongoing State Water Board activity within the greater Delta
watershed on instream flow requirements, habitat restoration, and triggering of basinwide water rights conditions.

· The FAS Declaration, which identifies critical reaches of each fully appropriated stream
system and times of the year when water is not available for appropriation, was last
updated in 1998. With projected shift of peak runoff earlier in the year, and shorter
precipitation seasons, the FAS Declaration will likely need to be updated to reflect
changing runoff timing and water availability.

· The State Water Board could implement some form of decision scaling to assist in the
quantitative assessment of future regional water availability. As work advances to
support regional decision making with watershed-scale climate vulnerability and
adaptation assessments, projecting streamflows under a range of warming and
precipitation change along with relative likelihood of potential climate outcomes could
support water availability analyses. Estimates of relative likelihood of potential climate
outcomes could be based on either a large ensemble, or probabilities associated with a
subset of global climate models recommended for California.
Amplified Hydrologic Extremes

6.3.1 Floods
Future floods are projected to be different from past floods in timing, frequency, magnitude, and form, with critical consequences for reservoir management, water storage, and water availability. However, there is also substantial opportunity in flood flows – in particular, the potential to capture flood flows for storage and subsequent use during dry periods. Managed

well, California’s groundwater basins can provide a crucial buffer against drought and climate change. Future storage projects could consider underground storage, which has the potential to capture excess runoff that surface water storage cannot store due to space or flood limitations.
· Recognizing that capturing high flows is an important approach to build resilience, the
State Water Board has issued guidance on water rights permitting beneficial uses
associated with groundwater recharge. The State Water Board also developed
temporary permit pathways, and an optional streamlined permitting process for
obtaining a permanent water right for those that plan to divert high winter flows or flood
flows and store that water underground. The streamlined permitting process for
diverting water from high flow events to underground storage aims to support achieving
groundwater sustainability, and ensure diversions are protective of native fish and
wildlife. Additional benefits of groundwater sustainability projects may include preparing
for changes in hydrology related to climate change, and increasing resilience of water
supply.

· There is also a significant opportunity to leverage ongoing studies and programs related
to climate change. For instance, DWR work to update and refine the regional flood
management strategy in the Central Valley Flood Protection Plan and for implementation of Flood-MAR, can help better understand the potential frequency of high-flow events (Tuolumne River and Merced River pilot studies).

6.3.2 Drought
Drought affects the availability of water for existing water right holders. Drought also affects the management and protection of the state’s ecosystems. During a drought, the State Water Board may determine there is not enough water available to serve all right holders and may curtail junior water rights, or may need to implement broad water right curtailments to preserve critical instream flow for endangered or threatened fisheries. With droughts projected to become more severe and last longer, the State Water Board may need to implement curtailments more often, for longer durations, and in an increasing number of watersheds (Schwarz 2015).
The State Water Board has already started efforts to evaluate and assess actions from the
recent droughts and use the lessons learned to inform responses for future droughts. Studies of the last four major droughts distilled recommendations to improve future drought responses (Green Nylen et al. 2018), and suggested that proactive drought response planning and preparation are key components of effective climate adaptation. For example, the most recent drought of 2012-2016 required swift action to streamline the curtailment process. In the absence of established instream flows or methodologies, the State Water Board had to adopt emergency regulation establishing minimum flow requirements to protect critical flows for anadromous fish in priority watersheds during the drought (State Water Board 2014b, State Water Board 2015a). While emergency regulations are temporary, the State Water Board had to expend significant effort to make numerous determinations on an expedited basis, with a limited public process.

Among opportunities to plan and prepare for future droughts are:
· Conduct and utilize instream flow analyses to further develop instream flow
recommendations for ecologically important streams to protect public trust values.
Development of instream flow requirements is a key strategy needed to protect
communities, fish, and wildlife in the event of droughts lasting multiple years, which is
an expected outcome of climate change. Quantifying the timing, quality, and volume of
flows reasonably protective of fish and wildlife beneficial uses for all California streams
may reduce the need for possible future emergency regulations and other short-term
efforts to establish instream flows during droughts. Developing new tools for identifying
functional ecosystem flows, and establishing criteria for watersheds statewide, starting
with watersheds with the greatest need, might also have an added benefit to applicants,
minimizing the need to conduct site-specific studies, and providing an avenue for
quicker application processing.

· Development of a rigorous curtailment methodology that can easily, quickly, and openly
describe to water managers and other stakeholders the order of curtailment priorities.

· Development of either standard terms (terms that are added to all water right permits
that meet certain criteria) or project-specific permit terms to address climate change
considerations.

7 Recommendations for Incorporating Climate Change into Water Rights
Permitting Policies, Procedures, and Methodologies
Climate change will pose increasing and new challenges to water management in California.
The following list of staff recommendations offers a menu of options to make water availability analysis more robust, and actions to support an effective water rights response to climate change. Generally, there are two pathways to implement recommendations, either on a caseby-case basis, or by adopting regulation. These recommendations are preliminary and will require further exploration through stakeholder and Board engagement, possible regulatory changes, and additional staff resources to fully implement.
7-1. Leverage Existing Climate Change Data in Permitting Water Availability Analyses:
The water availability analyses needed for permitting a new water right should account
for impacts of climate change, specifically changing runoff patterns and projected
changes in hydrology. The State has developed a considerable amount of data on
impacts of changing climate on California’s water resources. Staff’s recommendation is
to require applicants to use existing data, as available, to explore the potential impacts of
climate change in permitting water availability analysis. The two notable sources that
applicants could use are: 1) climate change data, tools, and guidance developed by the
Department of Water Resources for groundwater sustainability planning, and; 2) climate
simulations used in California’s Fourth Climate Assessment.
Where a better watershed-specific model exists, water rights applicants may use other
best available data and science to provide understanding of the projected future water
availability. This approach would provide applicants with flexibility to customize their

water availability analysis and capitalize on existing studies. Some applicants are
already leveraging pilot studies in their watersheds, or using data outlined above to
include climate change in their water availability analyses. Early implementation for
select projects would likely serve as examples for other applicants.
7-2. Include Adaptive Permit Terms in New Permits: Staff recommendation is to develop
climate change-related terms that are triggered by the occurrence of certain hydrologic
conditions as a way to make water rights responsive to future conditions. For instance, if
climate change modeling informed project development, the permit could authorize
adaptive changes to terms that include shifts in the rate or season of diversion. An
adaptive permit term in that case would include a diversion commencement trigger that
would allow a shift in diversion rate or season once projected conditions occur. Or, as
another example, the State Water Board could consider permit terms triggered by a
drought declaration. An adaptive permit term could restrict municipal and domestic
beneficial uses to only human health and safety needs during declared drought
emergencies.
7-3. Implement Tiered Requirements for Climate Change Analysis: The State Water
Board could require a varying level of climate change analysis in new applications based
on tiers as a way to reasonably balance the need for accurate water availability
projections and applicant cost/workload. Most pending water right applications are from
small diverters who are unlikely to have the resources or technical means to conduct
advanced climate change analyses. In a tiered approach, certain project characteristics
would trigger a requirement for a more rigorous analysis. For example, a more nuanced
analysis required for a higher tier may entail the use of global climate models to assess
the potential future impacts of climate change on the availability of water from the
requested water source. A lower tier analyses could require using an extended historical
time series of precipitation and streamflow data as a proxy for the potential future
impacts of climate change, or use climate datasets developed by the State.
Tiers could be established based on project characteristics, such as size (a threshold
based on a proposed diversion rate and/or a quantity), location (e.g., within specific or
prioritized watersheds, such as the San Joaquin River, the Tulare Lake Basin, the North
Coast Instream Flows Policy area, etc.), type (e.g., a specific beneficial use, for example
Municipal, and other uses with hardened demand, or climate-sensitive supply or season,
such as snowmelt-dominated runoff), or another metric.
7-4. Develop Fact Sheet for Water Right Applicants to Incorporate Climate Change: The
proposed season of diversion, rate, and quantity requested cannot be increased once a
new water right application is filed. In order to support potential water right applicants in
developing projects that will remain feasible in the future, the State Water Board could
develop a fact sheet to provide an overview of existing climate data developed for
California, and to advise that parties consider how climate change could affect water
availability, and evaluate proposed season, rate, and volume of diversion.
7-5. Strengthen the Minimum Period of Record Requirement for Streamflow Data:
Because recent precipitation and streamflow data may not capture the full range of
hydrologic variability, a longer streamflow record may better characterize climatic and

hydrologic variability of the stream system. The additional streamflow data may help to
identify wet and dry trends, extremes, and variability to improve the accuracy of
permitting water availability analysis. In the North Coast Instream Flows Policy area
there is a requirement to include no less than 10 years of data when developing water
availability information. Although no such requirement exists elsewhere in the state,
typical water availability analysis includes the entire period of record for a gage.
Additionally, the State Water Board could require longer and/or more complete
hydrologic records as part of the application review process.
7-6. Require more Rigorous Analytical Methods to Extrapolate Data to Similar
Geographic Areas: Hydrograph changes driven by climate change may exacerbate
inaccuracies when estimating unimpaired streamflow in ungaged watersheds, and as a
result it may be necessary to reevaluate the approach and identify alternative
methodologies that increase accuracy of water availability estimates. One way to
improve accuracy may be temporary installation of a portable stream gage(s) at
requested points of diversion to pair estimated values based on a reference gage with
measured streamflow. Another way may be using a greater number of alternative
reference sites with stream gage data to increase the range of historical, climatic, and
hydrologic variability captured by the analysis.
7-7. Expand Existing Network of Stream and Precipitation Gages: Because there is
often not enough hydrologic data due to the low number of gages, maintaining existing
gages and expanding the network of stream and precipitation gages is critical.
Increased collection and availability of pertinent hydrologic data would support improved
accuracy of future water availability analyses. Installing more gages may require
increased coordination and leveraged funding with other agencies such as U.S. Geologic
Survey, DWR, and California Department of Fish and Wildlife.
7-8. Reevaluate the Existing Instream Flow Metrics and Criteria: It may be necessary to
modify existing instream criteria and metrics to better protect migration paths, spawning,
and rearing for anadromous fish in a changing hydrology. Research and development of
scientific literature that assesses the hydrological impacts of climate change on
anadromous fish species will be needed to implement this recommendation.
7-9. Revise the Fully Appropriated Stream (FAS) List. State Water Board Resolution No.
98-08 (FAS Declaration) identifies critical reaches of each fully appropriated stream
system and times of the year when water is not available for appropriation. With
projected shift of peak runoff earlier in the year, and shorter precipitation seasons, the
FAS Declaration may need to be updated. There could be potentially more FAS
designations needed during the spring through fall due to changes in runoff and
precipitation timing. Conversely, some fully appropriated streams may need to be
reopened in order to allocate winter high-flow or flood events.
7-10. Prepare for and Capitalize on Capturing Flood Flows and Storing them
Underground: Floods and the magnitude of the peak flows are expected to increase
under many climate change projections. As a result, there may be greater opportunity to
divert flood and high flows during the winter to underground storage. The State Water
Board could build on DWR’s efforts to update and refine hydrology projections, and

leverage data and tools supporting the Central Valley Flood Protection Plan update and
implementation of Flood-MAR. These efforts may help to better understand the potential
frequency of high flow events and floods as part of permitting water availability analyses,
and to inform conditions for the resulting water right permits to ensure diversions are
protective of native fish and wildlife.
7-11. Plan for Droughts: As droughts are projected to become more severe and last longer,
the State Water Board may need to implement curtailments more often and in an
increasing number of watersheds. The State Water Board is already evaluating and
assessing what actions were successful during the most recent drought, and there are
additional steps that could aid in preparing for challenges that are to be expected with
future severe droughts:
· Conduct and utilize instream flow analyses to further develop instream flow
recommendations for ecologically important streams to protect public trust values,
which will reduce the need for possible future drought emergency regulations and
other short-term instream flow efforts.

· Prioritize the development of a curtailment methodology that can easily, quickly, and
openly describe to water managers and other stakeholders the order of curtailment
priorities and who is affected.

7-12. Coordinate with Other Agencies and Partners: The State Water Board will need to
coordinate and leverage efforts with other agencies and partners involved in water
resource management and adaption to climate change. With a growing body of
research, there is an opportunity to build upon the knowledge and gains made by State
and other agencies. Potential areas of collaboration include:
· Leverage DWR Climate Change Program work to inform the implementation of
SGMA, Flood-MAR, and other initiatives, coordinate efforts to improve and expand
projections of hydrologic responses to climate change, and develop tools that can
support water availability analysis.

· Examine opportunities for coordinating programs and jointly funding climate change
science to improve water availability projections from hydrologic modeling.

· Conduct joint climate change/water availability workshops.

· Learn from successful climate change-related water availability work in other states
and countries.

· Coordinate with the Delta Stewardship Council’s Delta Region Climate Change
Vulnerability Assessment and Adaptation Strategy, especially as related to instream
flows, habitat restoration, and triggering of basin-wide water rights conditions.

· Support opportunities to meet legal standards in creative, collaborative ways, such as
through voluntary solutions that enhance flows and habitat.

8 References
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