Which species will survive? Climate change enhances the vulnerability of California freshwater fishes to severe drought

By Peter Moyle

As I write this on an October weekend, rain is falling steadily in Davis and has been for most of the day. This is the first real rain we have had in over seven months. But it is not the end of the drought. Multiple storms are needed. The landscape is a dry sponge, reservoirs are empty, water rationing is in place or expected to be, and aquatic species are in decline. Water agencies are trying to capture all the water they can behind dams with bypass flows for fish minimal. But what if ‘normal’ winter storms do not arrive and this record drought continues? My specific worry is for the native fishes of California, which need some of this year’s water to survive. Unfortunately, for many of these these fishes, drought is almost perpetual because dams, diversions, and other factors take or alter the water they need to survive every year.

California has a very special native fish fauna in its inland waters. Most (83%) of the 130 or so species are endemic to the state and most (80%) are in decline even without considering the effects of climate change and continuing drought. Added to this are over 40 species of non-native fishes that are irrevocably here and mostly doing well. About 10 years ago, a team at the Center for Watershed Sciences (me, Joe Kiernan, Rebecca Quiñones, and Pat Crain) developed a scoring system to predict vulnerability of fishes to climate change, especially severe drought (Moyle et al. 2013), using 20 metrics. Ten of these metrics were ‘baseline’ measures related to population size and trends, life history, and dependence on human intervention. The other ten were related to climate change such as physiological tolerances, dispersal ability, and ability to adjust to habitat change. For the climate change study, we evaluated 121 native species and 43 non-native species, and found 83% of the native species were critically or highly vulnerable to the negative effects of climate change (see graph below). Critically vulnerable species (31%) were species for which the path to extinction has already been accelerated by climate change, especially by severe drought that is a consequence of global warming. Salmon and native trout species are especially vulnerable to climate change: 22 kinds are considered to be highly vulnerable for reasons described in the report below, written by Moyle et al. (2017) for California Trout. In fact, the last fish to slide into extinction in California was the bull trout, in the 1970s.

This report and lengthier one with supporting information are available from California Trout.

Below is a list of species that in 2012 were rated as critically vulnerable to climate change. Today, I would add another 15 species to the 37 already on the list because their scores were close to the arbitrary cut-off between critically and highly vulnerable ratings in 2012 and because of drought-driven demand for the water in which they live. New species to list include northern roach, Sacramento splittail, Santa Ana speckled dace, Lost River sucker, shortnose sucker, Goose Lake redband trout, Lahontan cutthroat trout, and seven pupfish species/subspecies. The bottom line is that most native California fishes are on an extinction trajectory and their highly altered habitats are being taken over by non-native fishes. Of 124 extant species of native fishes, only 22 can be regarded as having a safe future (e.g. Tahoe sucker, Sacramento pikeminnow, coastal rainbow trout) and only three seem to fit the IUCN definition for Green-list species, once-threatened species that have recovered to occupy much of their native range as the result of human actions (Akcakaya et al. 2018, Grace et al. 2021[1]). The three ‘recovered’ species are California golden trout, Little Kern golden trout, and Modoc sucker. Long-term recovery, however, depends on continued active management.

Distribution of climate change vulnerability scores for native and non-native species in California. From Moyle et al. (2013). Highly vulnerable native fishes, top left to right, to bottom: Red Hills roach, Delta smelt, Sacramento splittail. Note that non-native species generally have low vulnerability, in contrast with native species.

We have to keep in mind that our native fishes are in decline largely because of adverse land and water use combined with invasions of non-native species. Climate change threatens long-term survival, while our current actions (or lack of them) threaten short-term survival, as delta smelt and winter-run Chinook salmon demonstrate. The most positive thing that can be said about the status of California’s native fishes is that none have become extinct in the state since the 1970s.

List of species critically vulnerable to climate change developed by Moyle et al. (2013) in 2012. Species with ++ by the name are species that appear to be somewhat less vulnerable at the present time i.e., the threat of extinction is less immediate than once thought, due to better information or positive effects of management. Species marked with # have increased their vulnerability since 2012. 

Goose Lake lamprey

Kern Brook lamprey#

Cowhead tui chub

Clear Lake hitch


Long Valley speckled dace#

Amargosa speckled dace

Owens speckled dace#

Red Hills Roach

Modoc sucker++

Klamath Largescale sucker

Razorback sucker

Longfin smelt#

Delta smelt#

Upper Klamath-Tr spring Chinook#

Sacramento winter Chinook#

Central Valley spring Chinook#

Central Valley late fall Chinook

Central Valley fall Chinook

Central Coast coho

SONCC coho#

Pink salmon[2]

Chum salmon

N Calif. coast winter steelhead

N Calif. coast summer steelhead#

Klamath Mountains summer steelhead#

Southern California steelhead

McCloud River redband trout#

Eagle Lake Rainbow trout#

Kern River Rainbow trout

California golden trout

Little Kern golden Trout

Coastal Cutthroat++

Paiute cutthroat++

Shoshone pupfish

Cottonball Marsh pupfish

Unarmored threespine stickleback

Extinctions of our endemic species can only be prevented through science-based management strategies that take both species and their habitats into account, using an ecosystem-based approach (Mount et al. 2019) that accommodates both immediate and long-term problems. There is some hope for using this developing approach, following Governor Newsome’s rapid adoption of the 30-30 policy of the UN, which has the goal of protecting biodiversity in 30% of the land and ocean by 2030. 

For this to work for fishes and other aquatic organisms in California, aquatic ecosystems managed for biodiversity must be distributed across California’s diverse landscape. Grand schemes to protect and appropriately manage biodiversity in large regions (e.g. Watson et al. 2020, Obura et al. 2021) must specifically include aquatic ecosystems. Aquatic ecosystems tend to appear as small parts of the total landscape, although they are strongly affected by what goes on in the terrestrial systems in which they are imbedded. California, with its high endemism of fishes and other aquatic/riparian organisms, should be a leader in implementing such a strategy. Conceptually, California needs a system of Freshwater Protected Areas (FPAs), akin to the Marine Protected Areas (MPAs) that have been designated along the California coast. It is clear that our current ad hoc system of Wild and Scenic Rivers, reserves, parks, and similar areas is not working well for native fishes (Grantham et al. 2017).

The starting point could be the FPA proposals developed by the Moyle lab in the 1990s, then called Aquatic Diversity Management Areas. The basis for FPAs is a classification system for inland waters of California (Moyle and Ellison 1991): all ca. 160 habitat types should be represented in FPAs. Ideally most FPAs would be watersheds that contained multiple habitat types and multiple endemic species. Moyle et al. (1996) proposed a system of 44 FPAs in the Sierra Nevada as part of the Sierra Nevada Ecosystem Project, using criteria discussed in Moyle and Randall (1998). Another 50 or so proposed FPAs are on file. Various other iterations of a grand scheme to protect aquatic biodiversity statewide have been developed, but Moyle (2002) has the most fully developed description of a proposed system of FPAs for fishes.

The three fishes most likely to become extinct next in the wild are Sacramento winter-run Chinook salmon, Delta smelt, and Long Valley speckled dace. All are on life support through artificial propagation and artificial habitats. Costs can be high and extinction still possible, even likely. Are we expecting to treat the next 50 fish species headed for extinction in the same manner?

When you lose a species, it’s forever.

Phil Pister.

[1] A formal analysis of fit to IUCN Green status has not been performed; this is an informal assessment.

[2] Pink and chum salmon are abundant north of California but reproducing populations in CA, the southern most of the species, seem to be gone.

Further reading:

Akçakaya, H.R., and 10 others. 2018. Quantifying species recovery and conservation success to develop an IUCN Green List of Species. Conservation Biology 32(5): 128-1138.

Grace, M. K. and 172 others. 2021. Testing a global standard for quantifying species recovery and assessing conservation Impact. Conservation Biology 35:1–17. https://doi.org/10.1002/cobi.13756

Grantham, T. E., and 10 others. 2017.  Missing the boat on freshwater fish conservation in California. Conservation Letters 10:77-85. https://doi.org/10.1111/conl.12249

Howard, J.K, and 12 others. 2018. A freshwater conservation blueprint for California: prioritizing watersheds for freshwater biodiversity. Freshwater Science 37(2):417-431. https://doi.org/10.1086/697996

Mount, J., and 12 others. 2019. A Path Forward for California’s Freshwater Ecosystems. San Francisco: Public Policy Institute of California. 32 pp. https://www.ppic.org/wp-content/uploads/a-path-forward-for-californias-freshwater-ecosystems.pdf

Publications to support establishment of Freshwater Protected Areas

Moyle, P. B., and J. Ellison. 1991. A conservation-oriented classification system for California’s inland waters. California Fish and Game 77:161-180.

Moyle, P. B., and R. M. Yoshiyama. 1994. Protection of aquatic biodiversity in California: A five-tiered approach. Fisheries 19:6-18.

Moyle, P. B. 1995. Conservation of native freshwater fishes in the Mediterranean type climate of California, USA: a review. Biological Conservation 72: 271-280.

Moyle, P. B., P. J. Randall, and R. M. Yoshiyama. 1996. Potential aquatic diversity management areas of the Sierra Nevada. Pages 409-478 in Sierra Nevada Ecosystem Project: Final report to Congress, Vol. III, assessments, commissioned reports, and background information. Davis: University of California, Centers for Water and Wildland Resources.

Moyle, P. B., and P. J. Randall. 1998. Evaluating the biotic integrity of watersheds in the Sierra Nevada, California. Conservation Biology 12:1318-1326.

Moyle, P. B. 2002. Inland Fishes of California. Revised and Expanded. Berkeley: University of California Press. 502 pp.

Moyle, P.B. and M. P. Marchetti. 2006. Predicting invasion success: freshwater fishes in California as a model. Bioscience 56:515

Moyle, P.B., J. D. Kiernan, P. K. Crain, and R. M. Quiñones. 2013.Climate change vulnerability of native and alien freshwater fishes of California: a systematic assessment approach. PLoS One. http://dx.plos.org/10.1371/journal.pone.0063883

Moyle, P.B., R. M. Quiñones, J.V.E. Katz, and J. Weaver. 2015. Fish Species of Special Concern in California. 3rd edition. Sacramento: California Department of Fish and Wildlife. https://www.wildlife.ca.gov/Conservation/Fishes/Special-Concern

Moyle, P., R. Lusardi, P. Samuel, and J. Katz. 2017. State of the Salmonids: Status of California’s Emblematic Fishes 2017. Center for Watershed Sciences, University of California, Davis and California Trout, San Francisco, CA. 579 pp

 Obura, D. O. and 16 others. 2021. Integrate biodiversity targets from local to global levels. Science 373 (issue 6556): 746-748.

Saunders, D.L., J. J. Meeuwig, and A.C.Vincent. 2002. Freshwater protected areas: strategies for conservation. Conservation Biology, 16(1): 30-41.

Watson, J.E., D.A. Keith, B.B. Strassburg, O. Venter, B. Williams, and E. Nicholson. 2020. Set a global target for ecosystems. Nature 578:361-362

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Managing Water Stored for the Environment During Drought

By Sarah Null, Jeffrey Mount, Brian Gray, Michael Dettinger, Kristen Dybala, Gokce Sencan, Anna Sturrock, Barton “Buzz” Thompson, Harrison “HB” Zeff


Storing water in reservoirs is important for maintaining freshwater ecosystem health and protecting native species. Stored water also is essential for adapting to the changing climate, especially warming and drought intensification. Yet, reservoir operators often treat environmental objectives as a constraint, rather than as a priority akin to water deliveries for cities and farms. Reservoir management becomes especially challenging during severe droughts when surface water supplies are scarce, and urban and agricultural demands conflict with water supplies needed to maintain healthy waterways and wetlands. In times of drought, most freshwater ecosystems suffer.

This blog post examines 2021 water year actions by the federal Central Valley Project (CVP) and the State Water Project (SWP), which sought to maximize water deliveries while meeting environmental regulatory standards in a severe drought. Based on this experience, we offer recommendations to better protect the environment if California is faced with dry conditions in 2022 or beyond.

Priorities versus Constraints

The CVP and SWP (the “projects”) are designed principally to store and deliver freshwater to cities and farms. During droughts, the projects’ highest priority is to meet these supply obligations while complying with downstream water quality, flow, and endangered species requirements and meeting water delivery obligations to wildlife refuges. In this context, environmental standards operate as a constraint on project operations, rather than as a water supply priority. One of the most explicit examples of this is Congress’s 2016 directive that the biological opinions governing project operations must “provide the maximum quantity of water supplies practicable” to CVP and SWP contractors “without causing additional harm to the protected species.”

Project operations last spring illustrate the distinction between priority and constraint (see figure). Despite exceptionally low runoff during the winter, low reservoir storage at the end of winter, limited snowpack, and unusually warm and dry conditions, the CVP and SWP released significant quantities of water in April and May. These releases were made to meet water supply priorities for municipal and agricultural water contractors with senior water rights that predate construction of the projects.

By the end of spring, project reservoirs held insufficient water to meet water quality and flow requirements for the summer and fall. This especially harmed salmon, including winter-run Chinook that are close to extinction, because the reservoirs did not retain sufficient cold water to meet temperature standards in the upper Sacramento River. It also made it difficult for the projects to maintain water quality in the Sacramento-San Joaquin Delta for in-Delta users and Delta exports, ultimately requiring installation of a salinity barrier. The degraded water quality also is likely to take a long-lasting toll on a many native fishes.

In June, citing “critically  low  storage levels” in CVP and SWP reservoirs, the State Water Resources Control Board issued a temporary urgency change (TUC) order that relaxed environmental standards from June 1 to August 15. These changes might not have been needed if the projects had operated their reservoirs more conservatively in April and May.

No Room for Error

Delivering as much water as practicable to urban and agricultural users leaves no room to adjust for errors in forecasting or unanticipated worsening of conditions. Yet, as 2021 and previous drought years show, forecasting, modeling, and operational errors are the norm – not the exception – during droughts. These errors inevitably lead to increased harm to the environment and the likelihood of errors is increasing with a changing climate.

For example, in 2021 the projects used optimistic runoff and climate forecasts that over-estimated their ability to meet downstream temperature standards. These forecasting errors were compounded by unanticipated high diversions and in-stream losses, both above and within the Delta. The higher downstream water uses required larger reservoir releases to maintain Delta water quality and made managing water temperatures even more difficult. 

The problems of water year 2021 were not unique. Although different in detail, the same effort to deliver as much water as possible—coupled with modeling, forecasting, and operational errors—led to similar environmental problems in water years 2014 and 2015, the height of the last drought. In that drought, which was also warmer than normal, the State Water Board issued TUC orders that relaxed environmental standards.

Delayed Institutional Responses

A major challenge in drought management is the inability of project operators and regulatory agencies to respond quickly enough to head off problems. By early March, it was evident that it would be difficult for the CVP and SWP to meet both their supply commitments and their environmental obligations in 2021. This was reinforced in April when forecasted spring runoff failed to materialize. But in this drought, as in 2014 and 2015, there was a significant time lag between awareness of the problem in late winter/early spring and actions to address it, which occurred in the summer. 

As an example, a three-decade old State Water Board order (Order 90-5) requires the Bureau of Reclamation to develop a Temperature Management Plan (TMP) if there are likely to be difficulties meeting temperature standards below Shasta Reservoir. The Bureau submitted this plan in late May after extensive consultation among six state and federal agencies and their consultants. The Board approved the TMP in early June. But by that time it was too late to take corrective action by holding back more water in the reservoir, and the only remaining option was to modify water quality and flow standards. 

By late May, the State Water Board’s own models indicated the need to curtail some water rights below the reservoirs to enforce water rights priorities and protect several fish species. By June it was clear that unusually high downstream water use was going to make it difficult to meet Delta salinity standards, putting more pressure on reservoirs. 

The Board did not curtail junior water rights until June and began curtailment of most senior rights in late August. Unfortunately, these curtailments—especially those involving riparian and pre-1914 appropriative rights—came too late to reduce pressure on the reservoirs. 

Changes Needed to Manage Storage for the Environment during Drought

To better protect rivers and wetlands during drought, California must avoid the mistakes made in previous water years and droughts. This will require making environmental water supply a priority rather than a constraint, leaving a margin for errors in forecasting operations, and overcoming institutional hurdles to timely decision-making. These efforts should be accompanied by a strategy to improve water storage for ecological water uses, while reducing impacts on water deliveries to cities and farms. These reforms will be essential for adapting to protect ecosystem health in a changing climate.

Clarify Priorities

On September 21st of this year, the Director of the Department of Water Resources and the Regional Director of the Bureau of Reclamation stated in a hearing before the State Water Board that they intend to change the historical supply priorities of the projects, placing public health and safety first, environmental protection second, and water deliveries third.  

The details of this change in policy—including how it would function during drought—remain to be seen. But to be successful at reducing ecological harm during drought, it will require three additional actions.

Leave Room for Error

To make ecosystem health a priority, reservoir operators must end the practice of trying to maximize spring deliveries during droughts while hoping they will not violate flow and water quality standards later in the season. Operators also need to manage stored water more conservatively, allowing for a larger margin of error in early season runoff estimates and rethinking assumptions about climatic conditions. This would avoid reliance on TUC orders and other modifications of environmental standards to cover errors in forecasting and operation.

One approach to managing more conservatively would be to set aside ecosystem water budgets (EWBs) in reservoirs. These EWBs could function like a senior water right and be managed as a hedge against drought. Applied to reservoir operations, EWBs would guide decisions on how much water to carry over and reserve in the fall, what portion of winter and spring reservoir inflow to release, and what percentage of storage to assign for late season environmental releases.

Make Timely Decisions

Project operators, the fish and wildlife agencies, the State Water Board, and the water user community must work cooperatively to eliminate the institutional and procedural hurdles that prevent prompt actions to curb environmental harm. Start by planning for severe droughts every year, rather than reacting only when one occurs. This involves preparing annual environmental watering plans that account for current conditions and the impacts of previous years. The plans should function like a decision tree, describing the timing and type of decisions to be taken throughout the year, including course corrections if conditions change. The plans should be vetted with stakeholders and released at the beginning of every water year (October 1st).

Planning also needs regulatory support. The State Water Board can start by revising its requirements for temperature management in reservoirs to accommodate increasing drought severity, errors in forecasts and modeling, and the need to make decisions earlier in the water year. The Board also should update water quality control plans to incorporate increasing drought severity and to support timely decisionmaking, similar to ongoing efforts in the Colorado River basin. This would allow water managers to take measures that anticipate the effects of scarcity on supply and would enable the Board to make earlier decisions on curtailments.

Expand Storage Options for the Environment

The measures outlined above would entail increasing use of existing storage capacity to avoid environmental harm, especially during droughts. Additionally, expanding the volume of available storage for ecological uses will be key to adapting our water system to the changing climate. The array of Proposition 1 storage projects being considered by the California Water Commission is a start, as the public benefit of many of these projects focuses on improving drought supplies for the environment. One of these projects—Sites Reservoir—could become a model for operating storage to improve environmental management while reducing impacts on supply reliability for other water users, particularly by taking pressure off CVP and SWP reservoirs.  Underground storage in aquifers also has vast untapped potential. Some water managers already use innovative approaches to conjunctively manage water stored in reservoirs and groundwater basins to improve ecosystem health while also increasing available supplies. Examples include Yuba Water Agency’s conjunctive use program on the Lower Yuba River and groundwater banking projects in the Chino Basin and the Kern Water Bank. More efforts like these can reduce tensions between water supply and environmental management during drought and improve ecosystem outcomes.


Eight of the last ten water years have been warm and dry—part of a long-term trend of increasing drought intensity with unusually low runoff in springtime. To adapt to these changes without exposing freshwater ecosystems to increasing risk, and to avoid reliance on TUCs to ease environmental standards, new approaches to managing storage for both water supply and the environment will be needed. Water managers and regulators must set clear priorities to protect the health of rivers and wetlands, operate surface reservoirs more prudently, and respond quickly when drought is on the horizon. Despite the recent rains, we need to make these changes soon in case this drought continues into 2022 and beyond.

Aerial view of Shasta Dam, October 28, 2021. Photo credit: California Dept. of Water Resources

Sarah Null is the 2021-2022 CalTrout Ecosystem Fellow at the Public Policy Institute of California and an Associate Professor of Watershed Sciences at Utah State University.

Jeffrey Mount is a Senior Fellow at the Public Policy Institute of California’s Water Policy Center and Professor Emeritus of Earth and Planetary Sciences at the University of California, Davis.

Brian Gray is a Senior Fellow at the Public Policy Institute of California’s Water Policy Center and Professor of Law Emeritus at the University of California.

Michael Dettinger is a Visiting Researcher at Scripps Institution of Oceanography and Research Professor at Desert Research Institute. He is retired from the U.S. Geological Survey.

Kristen Dybala is a Principal Ecologist in the Pacific Coast and Central Valley Group of Point Blue Conservation Science.

Gokce Sencan is a Research Associate at the Public Policy Institute of California’s Water Policy Center.

Anna Sturrock is a UK Research and Innovation Future Leaders Fellow and Assistant Professor at the School of Life Sciences at the University of Essex.

Barton “Buzz” Thompson is the Robert E. Paradise Professor of Natural Resources Law at Stanford University and a Senior Fellow at the Stanford Woods Institute for the Environment.

Harrison “HB” Zeff is a Research Scientist of Environmental Sciences and Engineering at the University of North Carolina, Chapel Hill.

Further Reading

Abatzoglou, J. et al. “California’s Missing Forecast Flows in Spring 2021 – Challenges for seasonal flow forecasting”, CaliforniaWaterBlog.com, Posted on July 18, 2021.

Bardeen, S. “What It Means to Store Water for the Environment”, PPIC blog, Posted on July 26, 2021.

Grantham, T. et al. 2020 “Making the Most of Water for the Environment: A Functional Flows Approach for California’s Rivers, Public Policy of California report.

Lund, J. “The Big California Drought Stories of 2021”, CaliforniaWaterBlog.com, Posted on October 3, 2021.

Mount, J. et al. 2017 “Managing California’s Freshwater Ecosystems: Lessons from the 2012-2016 Drought, Public Policy of California report.

Mount, J. et al. 2018 “Managing Drought in a Changing Climate: Four Essential Reforms”, Public Policy of California report.

Moyle, P. and A. Rypel. “Drought Makes Conditions Worse for California’s Declining Native Fishes”, CaliforniaWaterBlog.com, Posted on June 27, 2021.

Null, S.E. and L. Prudencio. 2016 “Climate change effects on water allocations with season dependent water rights”, Science of the Total Environment 571: 943-954.

Rypel, A. et al. 2021 “A Swiss Cheese Model for Fish Conservation in California”, CaliforniaWaterBlog.com, Posted on January 24, 2021.

Willis, A. et al. “Dammed hot: California’s regulated streams fail cold-water ecosystems”, CaliforniaWaterBlog.com, Posted on August 29, 2021.

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Can one atmospheric river end California’s drought?

By Andrew L. Rypel and Jay Lund

Given the quantity and intensity of last week’s rain, an obvious question is: ‘Is the drought over?’ Alas, the answer is a resounding no. But, the data are interesting and worth thinking about in more detail.

Fig. 1. Accumulated precipitation for northern California is high at the start of the new water year. But, there is a long way to go to reach even average conditions. Graph from the Department of WaterResources, California Data Exchange Center  https://cdec.water.ca.gov/cgi-progs/products/PLOT_ESI.pdf

As of now, the 8 station index in the northern Sierra registers 12.6 inches of cumulative precipitation. Because the water year just started (October 1), all of this came from the recent atmospheric river. It was an impressive storm, and set quite a few local one-day precipitation records. This atmospheric river storm produced half as much precipitation as graced the region in all of last year (the 3rd driest year on record, 24 inches). This is roughly one fifth of an average year’s precipitation in just one day. This huge early storm also places us on a preliminary pace for the wettest year on record. But, the event was so early, that we have a long way to go to reach even average conditions.

We also have a major water deficit in soil moisture, empty reservoirs and groundwater to repay to end the drought. The storm did reverse the direction of storage in most reservoirs, from declining to climbing. Berryessa and Millerton are now both at 59 and 80% of capacity. But many large reservoirs remain extraordinarily low. The three largest (Shasta, Oroville, and Trinity) are at only 22%, 28% and 27% capacity, respectively. So while some systems have improved, larger ones require much more precipitation to recover. Nevertheless, this storm is an excellent start to the new water year.

Fig. 2. Reservoir levels as of 10/30/2021. Graph from the Department of Water Resources, California Data Exchange Center https://cdec.water.ca.gov/cgi-progs/products/rescond.pdf

Watersheds have been quite dry after two years of intense drought. The recent atmospheric river has wetted soils statewide, which will increase runoff to streams from later storms. Indeed dry soils were part of the reason why so little rainfall made it to reservoirs last year – the parched soils sucked it up. This buffer of dry soils reduces flooding as well. Further, the water that did hit the river must move through the state’s many empty reservoirs, further lessening downriver flooding.

Spawning pair of Chinook salmon on the Lower Stanislaus River. Photo source: Dan Cook (USFWS), downloaded from Wikicommons.org

The rain is welcome news for both humans and ecosystems. Firefighters who have fought two intense wildfire seasons are provided some relief for this fire season. And the water and flows will overall be positive for aquatic ecosystems, fishes, and forests. Adult Chinook salmon (O. tshawytscha) are ascending river systems to spawn or have already spawned; flows will assist in upriver passage of remaining adults, and longitudinal and lateral distribution of gloriously spawned-out carcasses/nutrients. For spring-run Chinook salmon who have successfully oversummered, these fish will be capable of ascending higher into the landscape to spawn. Outmigration survival of smolts increases non-linearly with flow (Michel et al. 2021). Thus, juvenile winter-run and late fall-run Chinook salmon and even steelhead (O. mykiss) smolts will benefit from these flows en route to the Pacific Ocean. Effects of such early flows on incubating and rearing salmonids are less clear. Increased flows will reduce water temperatures which will benefit eggs, although the high flows will likely also scour and destroy some salmon redds. But taken together, the rains will help our native fishes overall.

Importantly, this atmospheric river demonstrates important lessons about droughts, floods, climate change and California water. We should pay attention and learn from these events. First, perhaps paradoxically, flood events can occur in the midst of major drought. Correlations of precipitation across months in California are weak, so it is possible that recent wet conditions will be followed by a return to little precipitation that prolongs the drought. Such variations are a natural aspect of California’s hydrology. Also, climate change scientists have long-warned how climate extremes would become increasingly commonplace over time (Hayhoe et al. 2004, Cayan et al. 2008), making California’s hydrology even more like California’s hydrology. We can expect a continued real time roller coaster of extremes, accelerated by climate change, including drought, wildfire smoke, intense heat, flooding, mudslides etc.

Second, these moments expose how our water infrastructure will need to adapt with a changing climate. Interestingly, most climate change models do not show a major shift in average rainfall over time, but rather a shift in the timing and severity of storms and snowpack dynamics. California reservoirs were mostly designed to capture spring snowmelt from the Sierra. As more precipitation comes as rain, in more intense events like the recent atmospheric river, we might consider new approaches for storing water. Additional dams will not often be economical because 1) we already have dams in the most cost-effective locations; and 2) environmental costs of dams are increasingly obvious and contributing to declining salmon, smelt and the listing of new species under the Endangered Species Act (Moyle et al. 2017, Bork et al. 2020, Rypel et al. 2020). New and more environmentally sensitive modes of water storage are needed. This includes mountain meadows (Viers et al. 2013), beaver ponds (Baldwin 2015, Rypel et al. 2021), and expanded underground storage via groundwater recharge (Yao and Lund 2021). Given the constraints and timing of SGMA mandates, recharge of groundwater supplies will be especially critical in regions like the San Joaquin basin (Dobbin 2018, Gailey and Lund 2021).

So, it’s good news and bad news on the drought front. The atmospheric river clearly helped – soils have been quenched and some reservoir levels have increased. Fishes may find better fall conditions overall. Yet the drought is not over, and recovery may take awhile.  We have quite a soil moisture, reservoir, and groundwater deficit to recover – more than this one huge storm could provide.  It’s unclear what the rest of the winter may bring.

State and local agencies should be well-practiced by now in their drought plans, and should continue to plan for drought conditions that extend into the foreseeable future. Other managers in the water and environmental sectors will need to continue planning as the season wears on. California has a long history of innovating around the socioecological pressures that drought induces. Let’s all look at these events with an eye towards innovation once again.

Lake Oroville, May 2021. Photo credit: Frank Schulenburg, downloaded from Wikicommons.org.

Andrew Rypel is an Associate Professor and the Peter B. Moyle & California Trout Chair of coldwater fish ecology at the University of California, Davis. He is a faculty member in the Department of Wildlife, Fish & Conservation Biology and Co-Director at the Center for Watershed Sciences.   

Jay Lund is a Professor of Civil and Environmental Engineering Director, and Co-Director at the Center for Watershed Sciences at the University of California, Davis.

Further Reading

Baldwin, J. 2015. Potential mitigation of and adaptation to climate-driven changes in California’s highlands through increased beaver populations. California Fish and Game 101: 218-240.

Cayan, D.R., P.D. Bromirski, K. Hayhoe, M. Tyree, M.D. Dettinger, and R.E. Flick. 2008. Climate change projections of sea level extremes along the California coast. Climatic Change 87: 57-73.

Hayhoe, K., D. Cayan, C.B. Field, P.C. Frumhoff, E.P. Maurer, N.L. Miller, S.C. Moser, S.H. Schneider, K.N. Cahill, E.E. Cleland, L. Dale, R. Drapek, R.M. Hanemann, L.S. Kalkstein, J. Lenihan, C.K. Lunch, R.P. Neilson, S.C. Sheridan, and J.H. Verville. 2004. Emissions pathways, climate change, and impacts on California. Proceedings of the National Academy of Sciences 101: 12422-12427.

Michel, C.J., J.J. Notch, F. Cordoleani, A.J. Ammann, and E.M. Danner. 2021. Nonlinear survival of imperiled fish informs managed flows in a highly modified river. Ecosphere 12: e03498.

Moyle, P.B., R. Lusardi, and P. Samuel. 2017. SOS II: fish in hot water. California Trout and University of California Davis.

Viers, J.H., S. Purdy, R.A. Peek, A. Fryjoff-Hung, N.R. Santos, N.R., J.V.E. Katz, J.D. Emmons, D.V. Dolan, and S.M. Yarnell. 2013. Montane meadows in the Sierra Nevada: changing hydroclimatic conditions and concepts for vulnerability assessment. Center for Watershed Sciences Technical Report.

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Fish eyes: the hidden diet journal

by Miranda Bell-Tilcock

It is strange to think of an eye as a diet journal, but a fish’s eye can tell much about what it has been eating at each point in its life. If we know what a fish has been eating and when, then we can figure out where a fish has been. You just need to know where to look and how to understand what the eye is telling you. This approach formed the basis for our publication Advancing diet reconstruction in fish eye lenses in Methods in Ecology and Evolution. In this study, we used stable isotopes of carbon, nitrogen, and sulfur in fish eyes to better understand diet and habitat history of juvenile and adult Chinook Salmon (Oncorhynchus tshawytscha).

Stable isotopes such as carbon, nitrogen, and sulfur are natural markers found in the environment and can be integrated into tissues of fishes through diet (see Halloween blog). As a fish grows, many tissues eventually are replaced with new cells that isotopically resemble the habitat where the fish is currently feeding. This makes it difficult to track diet over a fish’s lifetime, with the exception of the eye lens. Fish eye lenses are onion-like spheres, rich in protein. Similar to onions, eye lenses are composed of individual layers that accumulate throughout a fish’s lifetime. Each layer represents a different time in a fish’s life. Applying stable isotope techniques with these individual layers helps researchers understand what and where a fish was eating.

Figure 1. Cross-section of juvenile Chinook Salmon weekly lens growth on the Yolo Bypass. Day 0 represents fish from the hatchery arriving to the floodplain enclosure experiment detailed in Jeffres et al. (2020)

When we applied this technique to the single adult Chinook Salmon, we could see that this fish had early life history values indicative of hatchery rearing. We then could identify when the fish reached the estuary before moving into the ocean. Once you isolate what habitat fish are using, then you can begin to quantify it for long term success.

With this study as a proof of concept, the tool can be applied to reconstruct juvenile life histories, and we can now begin to use it to quantify restoration efforts. Using Chinook Salmon as an example, we want to understand the long-term benefits of restoring and managing floodplains for juvenile salmon. We are now using this isotope tool in addition to the otoliths to reconstruct the life history of fish returned to spawn and understand the amount of time spent on floodplains before out-migrating to the ocean. This work will in turn help measure the success of restoration and management actions.

While this technique was particularly insightful for Chinook Salmon, its applications are not limited to salmon in California’s Central Valley. All over the world migratory species need freshwater habitat, and many of these environments are declining in quantity and quality. Understanding which habitats are important for fishes at different life stages can aid in conservation efforts and better tailor regulations and land and water management for recovery.

Miranda Bell-Tilcock is an assistant research specialist at the Center for Watershed Sciences, UC Davis. 

Further Reading:

Video peeling a juvenile Chinook Salmon lens

Listen to Science Friday: Seeing The World Through Salmon Eyes

Eye-Popping Research Helps Inform Salmon and Floodplain Management



Curtis, J. S., Albins, M. A., Peebles, E. B., & Stallings, C. D. (2020). Stable isotope analysis of eye lenses from invasive lionfish yields record of resource use. Marine Ecology Progress Series, 637, 181–194. https://doi.org/10.3354/meps13247

Granneman, J. E. (2018). Evaluation of trace-metal and isotopic records as techniques for tracking lifetime movement patterns in fishes. Graduate Theses and Dissertations. https://scholarcommons.usf.edu/etd/7675

Jeffres, C. A., Holmes, E. J., Sommer, T. R., & Katz, J. V. E. (2020). Detrital food web contributes to aquatic ecosystem productivity and rapid salmon growth in a managed floodplain. PLoS ONE, https://doi.org/10.1371/journal.pone.0216019

Kurth, B. N., Peebles, E. B., & Stallings, C. D. (2019). Atlantic Tarpon (Megalops atlanticus) exhibit upper estuarine habitat dependence followed by foraging system fidelity after ontogenetic habitat shifts. Estuarine, Coastal and Shelf Science, 225, 106248. https://doi.org/10.1016/j.ecss.2019.106248

Liu, B. L., Xu, W., Chen, X. J., Huan, M. Y., & Liu, N. (2020). Ontogenetic shifts in trophic geography of jumbo squid, Dosidicus gigas, inferred from stable isotopes in eye lens. Fisheries Research, 226, 105507. https://doi.org/10.1016/j.fishres.2020.105507

Meath, B., Peebles, E. B., Seibel, B. A., & Judkins, H. (2019). Stable isotopes in the eye lenses of Doryteuthis plei (Blainville 1823): Exploring natal origins and migratory patterns in the eastern Gulf of Mexico. Continental Shelf Research, 174, 76–84. https://doi.org/10.1016/j.csr.2018.12.013

Quaeck-Davies, K., Bendall, V. A., MacKenzie, K. M., Hetherington, S., Newton, J., & Trueman, C. N. (2018). Teleost and elasmobranch eye lenses as a target for life-history stable isotope analyses. PeerJ, 6, e4883. https://doi.org/10.7717/peerj.4883

Simpson, S. J., Sims, D. W., & Trueman, C. N. (2019). Ontogenetic trends in resource partitioning and trophic geography of sympatric skates (Rajidae) inferred from stable isotope composition across eye lenses. Marine Ecology Progress Series, 624, 103–116. https://doi.org/10.3354/meps13030

Tzadik, O. E., Curtis, J. S., Granneman, J. E., Kurth, B. N., Pusack, T. J., Wallace, A. A., Hollander, D. J., Peebles, E. B., & Stallings, C. D. (2017). Chemical archives in fishes beyond otoliths: A review on the use of other body parts as chronological recorders of microchemical constituents for expanding interpretations of environmental, ecological, and life-history changes. Limnology and Oceanography: Methods, 15(3), 238–263. https://doi.org/10.1002/lom3.10153

Vecchio, J. L. (2020). Isotope-based methods for evaluating fish trophic geographies. Graduate Theses and Dissertations. https://scholarcommons.usf.edu/etd/8306

Vecchio, J. L., Ostroff, J. L., & Peebles, E. B. (2021). Isotopic characterization of lifetime movement by two demersal fishes from the northeastern Gulf of Mexico. Marine Ecology Progress Series, 657, 161–172. https://doi.org/10.3354/meps13525

Vecchio, J. L., & Peebles, E. B. (2020). Spawning origins and ontogenetic movements for demersal fishes: An approach using eye-lens stable isotopes. Estuarine, Coastal and Shelf Science, 246, 107047. https://doi.org/10.1016/j.ecss.2020.107047

Wallace, A. A., Hollander, D. J., & Peebles, E. B. (2014). Stable isotopes in fish eye lenses as potential recorders of trophic and geographic history. PLoS ONE, 9(10), e108935. https://doi.org/10.1371/journal.pone.0108935

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Sometimes, studying the variation is the interesting thing

By Andrew L. Rypel

As scientists, we’re trained to key in on ‘response variables’. In my case, fisheries scientists often examine how fish physiology, populations, communities or whole ecosystems react to various environmental drivers or human alteration. Unfortunately, variation in data is too frequently looked upon as a nuisance, an after thought, or worse – a statistical hurdle distracting from presenting the cleanest possible pattern. Yet, what if the variation within the data was the interesting thing all along? Ecosystems are messy and dynamic, but in highly interesting ways. I continually return to this theme, and given that management is often a process of making decisions in the face of high uncertainty, studying variation on its own is probably worthwhile at some level.

Ecologists have long-recognized that understanding spatial and temporal heterogeneity in ecosystems is important. For example, studying spatial distributions of species is extremely common – some are clumped, others are more even, some are random. And population biologists have long-tracked temporal variation in population abundances. Classically, ecologists have linked variability in population numbers to the overall stability of populations and ecosystems (Pimm 1992; Fischer et al. 2001; Zhao et al. 2020). However, understanding relationships between spatial and temporal variability in ecological variables has been more difficult to unravel.

Now at this point, you might ask: Why would understanding such relationships matter? There are of course multiple answers, but at the most basic level, understanding variation is critical to predicting the behavior of dynamic systems. We know from theory and some empirical work in ecosystem and community ecology that spatial heterogeneity may predict temporal heterogeneity (Collins et al. 2018). In one empirical case, spatial variability in plankton production (greenness) in small lakes preceded temporal variation in plankton production (a plankton bloom) (Butitta et al. 2017). Thus, spatial variation may function as an early warning indicator or signal for regime shifts more generally (Nijp et al. 2019).

One of the original challenges in ecology was that replicated spatiotemporal data were exceedingly rare. This limitation is starting to change. Standard, replicated ecological studies and research programs have increased tremendously over the last 30 years. These include massive projects like the Long-Term Ecological Research (LTER) Program sponsored by NSF. Or the newer and more standardized NEON Project, also from NSF. In California, we have access to tremendous long-term monitoring data like the Fall Midwater Trawl Survey from CDFW, the CalCOFI survey, the Delta Juvenile Fish Monitoring Program from USFWS, the Suisun Marsh study started by Peter Moyle at UC Davis, and many others.

In a recent paper (Rypel 2021), I leveraged two unique but distinct datasets to examine spatial and temporal heterogeneity for fish population abundances in natural lakes in northern Wisconsin. Work at this site was started by colleagues at the University of Wisconsin, Center for Limnology as part of the North-Temperate Lakes LTER. Fish populations in these lakes have now been studied consistently for over 40 years – it is an incredible and underutilized data resource. A few key results emerged from the analysis:

Spatial and temporal variation is fish abundances is extraordinary. Populations regularly fluctuate by orders of magnitude within the same lake and across lakes. This is simply interesting – think about the effects of the human population in a given town going from 1,000 to 10,000 in a year or two. As for the spatial variation – this is expected, but it calls back to age-old questions as to why there are more or less animals that live in one ecosystem versus another (Hutchinson 1959).

Fig. 1. Bootstrapped temporal heterogeneity measures for 18 fish species in each of four lakes compared to bootstrapped spatial heterogeneity measures for the same species across 55 lakes regionally. Species like walleye were less heterogeneous in individual lakes over time relative to patterns observed spatially. Conversely, black crappie and yellow perch had high temporal heterogeneity in lakes relative to observed spatial heterogeneity.

The ratio of spatial to temporal heterogeneity is intriguing. Some species, like black crappie and yellow perch showed massive variations within individual lakes, but less variation across lakes. Other species like walleye showed huge spatial variation across lakes, but less variation within lakes over time (Fig. 1). These ratios likely say something about how different species are best managed.  For example, perhaps black crappie are best managed at a local level where common crappie habitats can be manipulated (coarse woody debris, water clarity etc). In contrast, walleye may require more of a landscape-scale strategy involving e.g., enhanced hydrologic connectivity or coordinating mitigation of large-scale impacts to lake riparian environments.

There is a strong relationship between the spatial and temporal heterogeneity. However, it was asymptotic in shape (Fig 2). Empirical studies exploring the relationship between spatial and temporal heterogeneity in ecological variables are scant. Results from this study highlight that spatial heterogeneity in fish abundances predicts temporal heterogeneity, but only at low levels of heterogeneity. Future work could build on these results by testing the generality of this pattern across different ecosystems, taxa, and life-history types.

Fig. 2. Relationship between spatial and temporal heterogeneity in abundance of fishes from north temperate lakes. Each bubble represents a single species, and size of the bubble scales to the number of lakes with temporal data (and thus confidence of temporal heterogeneity patterns). Dark line denotes a weighted non-linear (asymptotic) regression, and weighting was based on the number of lakes used in the mean temporal heterogeneity calculation.

One theme that emerged in this work, and others (Magnuson 1990), is that long-term ecological data are exceptionally important. In general, slow change tends to evade our senses, and if unaccounted for, can lead to blocked understanding. Long-term data are necessary for disentangling short-term variations in ecosystems from long-term trends.

I have been excited by the increase in outstanding synthetic ecological data work coming out of the California water community over the last several years (Stompe et al. 2020; Goertler et al. 2021; Mahardja et al. 2021). There is also new emphasis on boosting access to open data and to data and code provenance. Further exploration of our long-term open access data resources will have the potential to reveal insights on ecology and management. While we do, let’s consider the potential opportunities for describing and studying heterogeneity patterns. Developing an understanding for ecological variation may be critical to uncovering new ideas for protecting California’s native and declining biodiversity.

Further Reading

De La Rosa, G. 2021. Space & Time: Data that push the boundaries of ecology. https://lternet.edu/stories/space-time-data-that-cover-both-push-the-boundaries-of-ecology/

Butitta, V. L., S. R. Carpenter, L. C. Loken, M. L. Pace, and E. H. Stanley. 2017. Spatial early warning signals in a lake manipulation. Ecosphere 8(10):e01941.

Collins, S. L., M. L. Avolio, C. Gries, L. M. Hallett, S. E. Koerner, K. J. La Pierre, A. L. Rypel, E. R. Sokol, S. B. Fey, and D. F. Flynn. 2018. Temporal heterogeneity increases with spatial heterogeneity in ecological communities. Ecology 99(4):858-865.

Fischer, J. M., T. M. Frost, and A. R. Ives. 2001. Compensatory dynamics in zooplankton community responses to acidification: measurement and mechanisms. Ecological Applications 11(4):1060-1072.

Goertler, P., B. Mahardja, and T. Sommer. 2021. Striped bass (Morone saxatilis) migration timing driven by estuary outflow and sea surface temperature in the San Francisco Bay-Delta, California. Scientific reports 11(1):1-11.

Hutchinson, G. E. 1959. Homage to Santa Rosalia or why are there so many kinds of animals? The American Naturalist 93(870):145-159.

Magnuson, J. J. 1990. Long-term ecological research and the invisible present. BioScience 40(7):495-501.

Mahardja, B., V. Tobias, S. Khanna, L. Mitchell, P. Lehman, T. Sommer, L. Brown, S. Culberson, and J. L. Conrad. 2021. Resistance and resilience of pelagic and littoral fishes to drought in the San Francisco Estuary. Ecological Applications 31(2):e02243.

Nijp, J. J., A. J. Temme, G. A. van Voorn, L. Kooistra, G. M. Hengeveld, M. B. Soons, A. J. Teuling, and J. Wallinga. 2019. Spatial early warning signals for impending regime shifts: A practical framework for application in real‐world landscapes. Global change biology 25(6):1905-1921.

Pimm, S. L. 1992. The Balance of Nature? Ecological Issues in the Conservation of Species and Communities. University of Chicago Press.

Rose, K. C., R. A. Graves, W. D. Hansen, B. J. Harvey, J. Qiu, S. A. Wood, C. Ziter, and M. G. Turner. 2017. Historical foundations and future directions in macrosystems ecology. Ecology Letters 20(2):147-157.

Rypel, A. L. 2021. Spatial versus temporal heterogeneity in abundance of fishes in north-temperate lakes. Fundamental and Applied Limnology:Published Online, https://www.schweizerbart.de/papers/fal/detail/prepub/99848/Spatial_versus_temporal_heterogeneity_in_abundance_of_fishes_in_north_temperate_lakes.

Stompe, D. K., P. B. Moyle, A. Kruger, and J. R. Durand. 2020. Comparing and integrating fish surveys in the San Francisco Estuary: why diverse long-term monitoring programs are important. San Francisco Estuary and Watershed Science 18(2).

Zhao, L., S. Wang, L. M. Hallett, A. L. Rypel, L. W. Sheppard, M. C. Castorani, L. G. Shoemaker, K. L. Cottingham, K. Suding, and D. C. Reuman. 2020. A new variance ratio metric to detect the timescale of compensatory dynamics. Ecosphere 11(5):e03114.

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Episode 2: “Unraveling the Knot” Water Movement in the Sacramento-San Joaquin Delta – Tidal Forces

By William Fleenor, Amber Manfree, and Megan Nguyen

Tides are the biggest driver of Delta flows, and in Episode 2 we look at their impacts in different locations under a variety of inflow conditions.  Tides have a twice-daily cycle in the region, with a range of about six feet at Martinez.  In the first part of the animation, we remove all in-Delta controls and diversions and fix inflows at a common moderate early summer level to isolate effects of tidal forces from those of inflows, gates, and export diversions.  When the moon and sun are more aligned (full and new moon periods), tidal magnitude is greater.  Distances to the moon and sun influence tidal magnitude as do winds and barometric pressure.  Winds and barometric pressure are fixed in this animation.

The main lessons are:

  • Tidal ‘sloshing’ greatly exceeds Delta outflows. Tidal flows can be 400,000 to 600,000 cubic feet per second (cfs) at Martinez, while net outflows are often a few thousand cfs.
  • A given amount of tidal force exists at the Golden Gate, and a change in one location in the estuary has effects throughout.
  • Sacramento and Stockton Deep Water Ship channels have been deepened and straightened with dredging, which increases tidal flows up these channels and decreases tidal flows (and mixing) in other Delta channels.
  • Higher Spring tides, occurring when the sun and moon are more aligned, add volume to the Delta and by themselves can produce brief net negative flows on Old and Middle Rivers.

The second part of the animation varies Delta inflows to demonstrate how inflows and tidal forces interact, again without major Delta diversions.  We look at inflows lower than those previously shown, representing late summer, and two higher inflow levels.  Finally, we show effects of a flood pulse moving through the Yolo Bypass. The main lessons are:

  • Lower inflows increase tidally driven negative flows through Old and Middle Rivers.
  • As inflows increase, tidal influence diminishes from the upstream direction and net negative flows from the tides cease in Old and Middle Rivers.
  • Flood flows through the Yolo Bypass greatly reduce tidal influences.

Modeling produces a better understanding of natural and anthropogenic influences on Delta flows, which can help improve planning and policy-making for the Delta.

Coming next in Episode 3 is an examination of flow and salinity effects of major water diversions from the Delta.

William Fleenor is a senior researcher who specializes in hydrodynamics and hydraulic modeling at the UC Davis Center for Watershed Sciences. Amber Manfree is a postdoctoral researcher with the UC Davis Center for Watershed Sciences. Megan Nguyen is a GIS researcher at the Center for Watershed Sciences.

Further reading

A Tale of Two Deltas: A Comparison of Transport Processes in the Predevelopment and Contemporary Delta (Jon Burau, as summarized by Maven, 2016)

Episode 1: “Unraveling the Knot” – Water movement in the Sacramento-San Joaquin Delta – Introduction

Episode 2: “Unraveling the Knot” – Water movement in the Sacramento-San Joaquin Delta – Tidal Forces

Episode 3: “Unraveling the Knot” – Water movement in the Sacramento-San Joaquin Delta – Managing Flows

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The Big California Drought Stories of 2021

by Jay Lund

Happy New Water Year!  October 1, 2021 is the beginning of the 2022 water year in California, the traditional beginning of California’s “wet season”, such as it will be.

Although there are many fine and interesting stories from California’s current drought, so far, a few stories seem more important and worth summarizing (even though many have been widely covered). 

  1. This is a major drought.  The 2020 water year was the 9-th driest year of record and this last year has been the 3rd driest, in terms of precipitation.  Warmer temperatures in recent years have further reduced streamflow as more precipitation has evaporated back to the atmosphere before it could flow to streams or groundwater and further stressed ecosystems.  Although this is a major drought, in most regards it is not the worst drought California has ever seen, or will see.
  2. Most people and economic activity in California have been well-insulated from the drought.  Urban users have conserved little because they have not been convinced by their local utilities and governments that it is needed, and substantial conservation remains baked in from previous droughts, though much more is possible.  Indeed, from a short-term perspective, few urban areas have needed to conserve more.  Urban water management, responsible for about 20% of all human water use in California, has done quite well overall, so far.  There are, and will be, sizable economic damages from this drought, particularly in some local areas, but statewide, relative to California’s $2+ trillion/year economy, the drought is not a major economic event.  Overall, California can afford to focus on addressing particular drought weaknesses.
  3. Ecosystems are being hammered, especially salmon and forests.  This year’s winter-run salmon, already an endangered species, is essentially lost due to too-warm releases and low water levels in Shasta reservoir.  Other salmon runs are also suffering from low flows and warm temperatures.  Low reservoir levels will make it more difficult to avoid repeating these problems from reservoir operation next year.  Forest ecosystems are very dry, with longer and more severe fire seasons and likely many deaths of young and mature trees.  Many of these effects will be greatest after the drought in precipitation “ends.” (Moyle and Rypel)
  4. Agriculture is suffering, but mostly without catastrophe so far, because of increased groundwater pumping.  Groundwater withdrawals are most of the statewide agricultural response to drought.  Surface water storage has been helpful, but has far less storage capacity and is quite expensive to expand.  California’s agricultural prosperity during drought relies primarily on sustainable groundwater storage. (Medellín-Azuara)
  5. Rural drinking water wells are impacted by increased agricultural pumping.  Agricultural pumping lowers water tables and often strands shallower domestic and community wells in rural areas, affecting hundreds to thousands of rural wells.  Deeper agricultural pumping is also likely to accelerate the contamination of wells from nitrate in shallower groundwater.  Many of those depending on shallow rural wells rely on agricultural jobs.  Implementing the Sustainable Groundwater Management Act will help reduce rural drinking water well vulnerability to drought, but this hasn’t happened much yet. (Gailey)
  6. Increased groundwater pumping increases challenges and urgency of implementing SGMA. Under the Sustainable Groundwater Management Act, all the additional groundwater pumped during this drought must be replenished from reduced pumping and additional recharge before 2040.  Faced with droughts and climate change, groundwater plans will need to be made, implemented, and enforced with more spunk than most people have previously thought.  This immense challenge will require major painful long-term reductions in irrigated acreage in parts of the San Joaquin Valley. (Escriva-Bou et al)
  7. Higher temperatures are making seasonal runoff forecasts less reliable, with past forecast methods being too optimistic.  Snowmelt in 2021 was about 800 taf less than predicted, based on past relationships between snowpack and runoff.  This would be about a 10% over-prediction between runoff predicted and actual annual runoff – valuable water in a dry year. (Abatzoglou et al.)
  8. An additional dry year could make this drought a whopper.  Reservoir levels are everywhere nearing of exceeding new low levels, watersheds are parched, and groundwater tables are dropping.  So fewer water reserves would be available for a third dry year, and much more precipitation than usual will be needed for next year to not be dry.  One DWR official was recently reported as saying the coming year would have to be at 140% of average precipitation to achieve average annual runoff.  Historically, 140% of average precipitation is exceeded in only 27% of years.  Overall, we seem likely to see an additional dry year, in terms of runoff.  (There is little year-to-year correlation of precipitation in California from year to year, and in northern California, essentially no correlation with El Nino.)
  9. Many urban areas are preparing for an additional dry year by implementing new water rate structures which would encourage more drought and permanent water conservation while keeping urban water utilities financially solvent.  This seems like a good time for water users of all sorts to prepare for an additional dry year and future droughts.  Droughts are much less damaging with preparation.
  10. Long-term preparation gaps.  With the climate changing, and many areas having seen benefits from outstanding drought preparation, it is surprising that some areas still lack in preparing for droughts.  Drought plans for ecosystems and Delta management seem particularly needed.  These gaps reflect the greater difficulty and complexity of these problems and perhaps the lack of political will, evolved consensus, and effective organization to manage these problems.  Another year of drought might be needed to spur greater preparation.

These are challenging times for water in California, again.

Further readings

Abatzoglou, J. et al.California’s Missing Forecast Flows in Spring 2021 – Challenges for seasonal flow forecasting,” CaliforniaWaterBlog.com, Posted on July 18, 2021

Escriva-Bou, A., et al. “How reliable are Groundwater Sustainability Plans?”, CaliforniaWaterBlog.com, Posted on May 10, 2020

Gailey, R. and J. Lund. “Mitigating Domestic Well Failure for SGMA and Drought in the San Joaquin Valley”, CaliforniaWaterBlog.com, Posted on June 20, 2021

Lund, J. “2021 Drought in California – in one page”, CaliforniaWaterBlog.com, Posted on August 22, 2021

Medellín-Azuara, J. and Jay Lund, J. Jobs and Irrigation during Drought in California, CaliforniaWaterBlog.com, Posted on June 6, 2021

Moyle, P. and A. Rypel. “Drought Makes Conditions Worse for California’s Declining Native Fishes,” CaliforniaWaterBlog.com, Posted on June 27, 2021

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Developing tools to model impaired streamflow in streams throughout California

by Jeanette Howard, Kirk Klausmeyer, Laura Read, and Julie Zimmerman

Droughts are extreme, but not necessarily extreme events — at least not in the way we humans usually experience events as discrete, episodic occurrences. Droughts are continuous and exhausting; they can come out of nowhere and take us on a rollercoaster of waiting for precipitation to come, measuring when it does, and hoping it will be enough to keep our rivers flowing for human use and healthy ecosystems. Droughts may feel so extreme that they should be a rare occurrence, but they are a natural part of California climate. And they will become even more frequent – climate change predictions show that extreme events, such as droughts and floods, are becoming more common (Swain et al. 2018).

Droughts are also subjective: in a year like this one, there’s no question that all of California is experiencing a drought. However, many rivers and streams in California experience drought-like conditions almost every year because of human demands for water (Zimmerman et al. 2018) such as in the Sacramento-San Joaquin Delta where the estuary experiences drought-like conditions in most years (Reis et al. 2019). Yet in most rivers in the state, we don’t have enough historical data to know how much water should be available. For example, we often don’t know if a river is running dry because it is the river’s natural condition (a stream with naturally intermittent flow), or if it should always be flowing and is running dry because humans are using too much water at the wrong times.

To effectively and reliably manage water, we need to know (1) how much water needs to be in a river to protect species and ecosystems, (2) how much water is actually in the river, and (3) what is the gap between the two? There is currently a group of scientists from universities, agencies, and NGOs that developed a framework and set of tools to answer the first question for all rivers in California – known as the California Environmental Flows Framework (CEFF). But the second question – how much water is actually in the river – has been a tough nut to crack. Predictions of actual flows would greatly enhance the ability to apply the CEFF framework by enabling the assessment of flow alteration and provide quantitative targets for how much additional water is required instream.

Actual flow measurements are only available at a finite set of point locations across the state – stream gages that are installed and operated by USGS, DWR, or other entities. Work by The Nature Conservancy found that approximately 3,600 stream gages have been active on streams and rivers in California at some point, but only about half of those have been active recently largely due to a lack of funding (see https://gagegap.codefornature.org/). Even with this network of gages, 89% of streams are poorly gaged, which means that for 89% of streams in California we have no information on actual flows and no obvious way to estimate the gap between the river flow that is needed and the flow that is available.

Investments are needed to increase our network of gaged rivers and streams. But rather than measure flow at gages in every stream in the state, it would be more efficient, cost effective, and realistic to predict flows, using a robust and scalable approach. With these predictions, we can develop storylines that tell the tales of these rivers, tracing the hydrologic signatures of a river from its historically unimpaired flows, through transitions brought by alteration (e.g., diversions, dams, land use change), to its current state today and likely state in the future. To write these stories from end-to-end, The Nature Conservancy (TNC-CA) and Upstream Tech have partnered to develop a set of tools that can estimate river flow using dynamic satellite data and machine learning methods. We began by building a model to estimate actual river flow and compared those modeled predictions to stream gage data. Our work in 300 gaged basins across California indicates that the model we’ve developed performs well and can also estimate actual river flow in ungaged basins.

What could be the impact of this model for planning and management in dry years? Consider this example from the Yuba River near Marysville (drainage area = 1,339 mi2 [3,450 km2]):

Using our ‘unimpaired’ flows model, which predicts naturalized streamflow similar to a typical rainfall runoff model, the validation period shows a high bias in the model’s prediction during the spring snow-melt period. The observation record dates back to 1987, so we don’t know the flows here before the reservoirs were built upstream in the basin, but we do know that the signature is altered and that this model is not reflective of impaired flows today.

The challenge ahead of us is to capture this altered behavior such that we can make estimates given the current storyline of the river. The extra challenge: do it with public data sources that have information across many basins so that this approach is scalable and not dependent on difficult to obtain and maintain data (e.g. dam-specific operation plans). Using over 1,000 ‘enhanced basin characteristics’ that were collected from StreamCAT, USGS Gages II, and USGS channel alteration datasets, we enhanced our unimpaired flows model to create an actual flows model. Here’s the result at the same Yuba River site:

The model described the shift from a natural snow-melt signal to a longer and flattened spring peak, reflecting the altered current conditions in the watershed. The real kicker of this site and others like it in our study: this was one of our “test” sites, which in machine learning terminology means that it was hidden from the model during training and treated as ungaged. The model never saw any observations from this site, never saw this time period even at other sites, and still learned this behavior shift from the enhanced basin characteristic inputs that we gave it. The Nash-Sutcliffe Efficiency (NSE), a common goodness-of-fit metric in hydrology, improved from -2.7 in the unimpaired model (top plot) to 0.77 in the actual flows model (bottom plot). A perfect NSE is one.

In the next phase, TNC-CA and Upstream Tech are expanding this approach to predict historic daily flows in 350 basins from 2000-2020, further validating modeling of ungaged impaired flows. From there, we’ll work on expanding estimates to ungaged streams across the state.

In dry years better estimates of flow in ungaged streams can provide a lifeline of information for real and near-term operational decisions, curtailments in drought years, assessments of water rights applications, and many other decisions that require information about water availability. For example, this year the operational forecasts largely missed this drought’s severity. A model that can simulate historic daily flows in altered basins across California could be used in the future for forecasting daily and seasonal flows with confidence and be able to answer crucial questions for decision makers such as:

  • “Will we pass critical habitat thresholds next month?” (Environmental flows planning)
  • “What is the likelihood that flows will be between X and Y, yielding sufficient water for all users?” (Allocation decisions from daily to three-months out)
  • “What types of basins need more gages because the hydrology is difficult to model and the data can improve model predictions elsewhere?” (Gage gap analysis and gage prioritization)

As the climate changes, the data and models we use must keep pace. Let’s work together to discover the true stories of our rivers and how they can better shape our future relationship with water as a lifeline for humans and nature.

Jeanette Howard, Ph.D., is the Director of Science for the Water Program for The Nature Conservancy’s California Chapter. Kirk Klausmeyer is the Director of Data Science for The Nature Conservancy’s California Chapter. Laura Read, Ph.D., is a Product Manager of HydroForecast at Upstream Tech. She co-authored this blog, representing the technical work of Alden Keefe Sampson and Mostafa Elkurdy. Julie Zimmerman, Ph.D., is Lead Scientist for The Nature Conservancy’s California Water Program.

Further Reading:

California Environmental Flows Working Group (CEFWG). 2020. California Environmental Flows Framework. California Water Quality Monitoring Council Technical Report 37 pp.

Grantham, T. E., J. K. H. Zimmerman, J. K. Carah, and J. K. Howard. 2019. Streamflow modeling tools inform environmental water policy in California. California Agriculture 73(1): 33-39.

Reis, G.J., J.K. Howard, and J.A. Rosenfield. 2019, Clarifying effects of environmental protections on freshwater flows to – and water exports from – the San Francisco Bay Estuary. San Francisco Estuary and Watershed Science 17(1): 1-22.

Swain, D. L., B. Langenbrunner, J. D. Neelin, and A. Hall. 2018. Increasing precipitation volatility in twenty-first-century California. Nature Climate Change 8: 427-433.

Yarnell, S. M., E. D. Stein, J. A. Webb, T, Grantham, R. A. Lusardi, J. Zimmerman, R. A. Peek, B. A. Lane, J. Howard, and S. Sandoval Solis. 2020. A functional flows approach to selecting ecologically relevant flow metrics for environmental flow applications. River Research and Applications 36: 318-324.

Zimmerman, J. K. H., D. M. Carlisle, J. T. May, K. R. Klausmeyer, T. E. Grantham, L. R. Brown, and J. K. Howard. 2018. Patterns and magnitude of flow alteration in California, USA. Freshwater Biology 63: 859-873.

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Risk Rating 2.0: A first look at FEMA’s new flood insurance system

By Ryan Miller, Peter Hansen, and Nicholas Pinter

Risk Rating 2.0 has been called the Federal Emergency Management Agency’s (FEMA)’s most significant reform in 50 years.  Roughly 77% of customers of the National Flood Insurance Program (NFIP) nationwide will see increases in their premiums, while the other ~23% will see reductions or no change.  FEMA will formally introduce Risk Rating 2.0 on October 1, 2021, and most premium increases will kick in on April 1, 2022.

In brief, Risk Rating 2.0 moves the NFIP away from its heavy reliance on in-or-out flood zones, in particular in-or-out of the so-called “100-year floodplain,” and towards an individual assessment of risk for each property (as promoted in this Blog [6/16/2019]).  FEMA’s 100-year flood area will not go away – in particular, this will still be the basis for whether a property owner with a federal mortgage must buy flood insurance – but the premiums for each property will be determined based on individual factors that include flood risk from an ensemble of three privately developed flood models. 

The Data

Recently, FEMA published summaries of NFIP premium changes by state, with details down to individual zip codes.  This first glimpse of Risk Rating 2.0 is a limited one; for example it shows only first-year changes (increases are capped at 18%/year) and lumps the most extreme increases or decreases into bins of “greater than $100” per month.  Nonetheless, our group took the zip code-level data and “reverse engineered” that information to provide a first look at what policyholders and others interested in flood-risk management can expect from Risk Rating 2.0. 

The focus of this review is California.  Over the history of the NFIP, California has been a donor state, contributing hundreds of $millions more in flood insurance premiums than it has received in claims (California Water Blog 12/14/2016).  Under Risk Rating 2.0, 73.2% of California NFIP policyholders will see premiums increase, and 26.8% will see decreases. 

We encourage readers to explore Risk Rating 2.0 premium changes across California using our interactive map of average premium changes by zip code (Link to Interactive Map).

Premium Changes and Patterns across California

Statewide, the majority of Californians with NFIP policies can expect to see premium increases of less than $10 per month (Figure 1; Table 1).  That being said, the total amount of premium dollars paid by California policyholders as a whole is actually set to decrease.   The overall distribution of premium changes across California is bimodal – a large majority of policyholders will receive small rate increases, but some policyholders will receive larger discounts. Of the >20,000 policies receiving discounts of ≥$20 per month, nearly half are >$70/month. We cannot precisely calculate the total net impact of Risk Rating 2.0 on California because FEMA’s data masks the exact dollar amount of changes at the extreme tails (8 policies with increases >$100 per month and 7421 properties with decreases >$100 per month). For the purposes of this analysis, we conservatively assumed a $100 change for the extreme tails (+/- >$100/month). Using this method, the total change in premiums in the first year of Risk Rating 2.0 is an aggregate decrease of at least $1.4 million per month (= at least $16.76 million per year statewide), or ≥9.9% of total California NFIP premiums (FEMA, 2021b). About half of this estimated total discount discount will go to single-family homes (~165,000 policies), and the other half going to the remaining non-single-family and non-residential NFIP properties (~49,000) in California.

The overall downward shift in premiums is consistent with our earlier findings that NFIP seemed to be overestimating flood risk in California.  The state has been hit by more than its share of disasters, but several decades of flood data were not adding up to the flood hazard suggested by NFIP premiums until now.  In shifting to a more physical, individualized formula, Risk Rating 2.0 seems to be recognizing this earlier overestimate, although not correcting the formula as much as may be warranted. 

This bimodal distribution of premium changes is also interesting when mapped across California (Figure 2). Increases and decreases are scattered across the statewide zip codes, but a few regional patterns emerge. First, the California Central Valley – including the Sacramento Valley north of Sacramento and the San Joaquin Valley to the south – is characterized by average premium decreases. under Risk Rating 2.0 (greens in Fig. 2). 

Figure 1. Count of monthly premium changes to all California NFIP policies.

Stakeholders in the Central Valley have long complained that NFIP was overcharging them; for example, pressing the Government Accountability Office in 2014 to study perceived biases against agriculture baked into the NFIP (https://www.gao.gov/products/gao-14-583).  In addition, the California Central Valley has broad areas protected by levees, some of which meet the 100-year protection standard, some not. 

Figure 2. Approximate change in NFIP premium cost by California zip code, for all zip codes with at least 5 NFIP policies listed in that area.  Values shown are not true averages because policies listed by FEMA as changing by >$100/month were calculated as +/- $100.

Figure 3 maps out premium changes in the Sacramento area. Four of California’s top five zip codes with the most NFIP policies are located around Sacramento. Under Risk Rating 2.0, three of those (95833, 95834, and 95835 [Natomas]), will see modest declines in premiums. Conversely, 95831 (the Pocket area) will see premium increases. All four of these are levee-protected areas along the Sacramento River.  The US Army Corps of Engineers recently completed significant levee improvements around Natomas[1], and is commencing improvements to the Pocket area.[2]  Until now the NFIP handled levees as all-in or all-out, a practice widely criticized from all sides.  Under Risk Rating 2.0, the Corps has supplied FEMA with levee data, but estimates of levee reliability is notoriously difficult to quantify, and the new algorithm for levee protection is currently a black box that needs scrutiny.

Our own zip codes here in Davis illustrate some of the odd shifts under Risk Rating 2.0.  The 95616 zip code, including western Davis and the university, will see average decreases of almost $4.00 per month, while 95618 to the east will see increases >$4.00. Both areas lie at similar elevations and are largely outside of FEMA’s mapped 100-year floodplain.  The whole area is protected from flooding of the Sacramento River and other tributaries by levees and bypasses.  We initially suspected that the private-sector flood models embedded in Risk Rating 2.0 are favoring levee-protected areas, making this change in Davis puzzling, but a lack of transparency in underlying data obscures the mechanisms driving such changes.  

Figure 3. Average change in NFIP premium cost by ZIP Code, Sacramento area

Figure 4 shows Risk Rating 2.0 premium changes in the Los Angeles area. Within this region, changes are most pronounced in the foothills and coastal areas in Malibu, the Santa Monica foothills, and the Hollywood Hills, with policyholders in zip code 90265 (Malibu) set for an average discount of >$40/month. This represents the steepest discount for any zip code in California with >1,000 current policies. Elsewhere in L.A., the densely populated San Fernando Valley and main L.A. Basin area, on average, will see modest increases in monthly premiums.

Figure 4. Average change in NFIP premium cost by ZIP Code, Los Angeles area

The large premium decreases in Malibu, the Santa Monica foothills, and the Hollywood Hills are surprising.  FEMA is heavily marketing Risk Rating 2.0 as “Equity in Action.”  Malibu’s median household income is >$150,000 per year (2019), 2.5 to 3 times higher than the $50,000-$60,000 in most San Fernando Valley zip codes. 

Risk Rating 2.0 does include one important fix that promotes economic fairness.  Under the current NFIP pricing system, premiums are based on the insured value of a structure and not the actual value of that building.  And currently, coverage up to $60,000 is charged at a higher rate than coverage above that threshold.  FEMA originally did this to encourage policyholders to insure the full value of their structure and contents (up to allowable caps).  But the policy is regressive as well as counterintuitive, as high-value structures are also more likely to incur expensive damages.  Under Risk Rating 2.0, premiums will be priced based on a structure’s replacement cost. 

Beyond the clear fix in premium pricing above, it is unclear how much Risk Rating 2.0 lives up to its “Equity” label, either in intent or in its impact.  By all accounts, Risk Rating 2.0 was designed primarily and from the start as a new pricing structure to fix NFIP’s perennial funding shortfall.  As the Congressional Research Service put it, “Risk Rating 2.0 will continue the overall policy of phasing out NFIP subsidies.”  Fixing the perennial hemorrhaging of NFIP may be a worthy goal, as is making insurance rates that better reflect risk, but rolling out these changes under the banner of “Equity” is disingenuous. 

To preliminarily assess the economic equity of Risk Rating 2.0, we compared premium changes across California to median household incomes in the same zip codes (Table 2). There is no clear correlation between neighborhood income level and average premium change. Premium decreases were largest in the lowest-income category (averaging -$9.25/month for neighborhoods with incomes <$50,000).  Premium decreases were smallest for middle incomes (averaging -$3.43/month for neighborhoods with incomes $70,000-$80,000). Premium changes in all other income categories, including areas with mean incomes >$100,000, were intermediate, averaging -$6.50/month.

Other questions about Risk Rating 2.0 focus on the modeling and formulas used to calculate risk and premiums.  Some details have been provided (e.g., the “Milliman Report,” April 2021), but a lot of Risk Rating 2.0 is a black box.  Our research group is trying to obtain better, clearer data to assess questions like how coastal flooding and future climate change are reflected in the new RR2.0 premiums.  In the meanwhile, Figure 5 shows zip code-level premium changes for the San Francisco Bay Area. Here, it appears that many low-lying costal areas are set to experience premium increases, while foothill areas are set for significant discounts. Coastal zip codes like 94080 (South San Francisco), 94044 (Pacifica), and 94030 (Millbrae) are will see premium increases in the $5-%7 range, while mountainous, suburban areas like 94605 (Oakland Hills) and 94583 (San Ramon) are set for premium decreases >$20 per month. However patterns in the San Francisco Bay Area appear to run counter to the Los Angeles area: average premiums in low-lying coastal areas of San Francisco going down, versus scattered decreases in Los Angeles. Deconvolving the overlapping hydraulic, climatic, engineering, and actuarial changes embedded in Risk Rating 2.0 will require much more openness and data sharing on the part of FEMA and its partner modeling contractors.

Figure 5. Average change in NFIP premium cost by ZIP Code, San Francisco area


Risk Rating 2.0 is FEMA’s effort to bring about significant reform to the NFIP, with an eye toward incorporating more accurate flood risk information and, purportedly, more equitable premiums proportionate with that risk. Limited pricing data released by FEMA suggest that most California policyholder will see modest increases, whereas a smaller number of policyholders will see larger discounts which bring down the total NFIP bill to California by at least 10%.  Mapping these data highlights how these increases and decreases vary widely across the state, and FEMA continues to mask the “extreme tails” of the distribution (changes >$100/month, i.e., >$1200 per year) as well as changes beyond the first year of Risk Rating 2.0.  Also importantly, the premium decreases across California are smaller than the documented imbalance between what the state has paid into the NFIP as premiums and what its policyholders have received as payouts over the history of the program (California Water Blog, 12/14/2016). 

Answering questions about Risk Rating 2.0, like the one above, requires independent scrutiny of the modeling and assessing assumptions on which the new insurance premiums are based.  High on that list of important questions is how data provided to FEMA by the Army Corps of Engineers characterize flood risk behind different levees.  “Levee fragility” and “residual risk” behind levees are notoriously difficult to assess and quantify, and slightly different assumptions can mean huge differences in the insurance bills that policyholders are soon to receive. 

Starting on October 1 of this year, flood insurance customers eligible for renewal can lock in the new premiums under Risk Rating 2.0.  Policyholders should check with their insurance agent whether their bills are slated to go up or down, and if down, by all means they should reset as soon as possible.  On April 1, 2022, the new changes will apply to all new and renewing policies.   

While the apparent net decrease in California’s flood-insurance premiums is a welcome change, important questions remain about how private-sector flood models and assumptions about local risk (e.g., levee protection) are weighed in Risk Rating 2.0.  We call for more transparency and dialog with FEMA, including the sharing of additional information and data at a fine-grained spatial resolution.

Ryan Miller is a Ph.D. student in the Geography Graduate Group at UC Davis, researching flood and fire risks, climate change, and urban planning. Peter Hansen, MA is a geospatial specialist and IT consultant in the College of Behavioral and Social Sciences at CSU, Chico. Nicholas Pinter is the Shlemon Chair in Applied Geosciences in the Department of Earth and Planetary Sciences at UC Davis and is Associate Director, Center for Watershed Sciences.

Further Reading

California Department of Water Resources (DWR), 2021.  Central Valley Flood Protection Plan.  https://water.ca.gov/Programs/Flood-Management/Flood-Planning-and-Studies/Central-Valley-Flood-Protection-Plan

FEMA, 2021a.  Risk Rating 2.0: Equity in Action.  https://www.fema.gov/flood-insurance/risk-rating

FEMA, 2021b (Data as of: 07/31/2021).  Policy Information by State and Community.  Available from https://nfipservices.floodsmart.gov/reports-flood-insurance-data

First Street Foundation, 2021.  Find Your Home’s Flood Factor.  https://floodfactor.com/

Pinter, N., R. Hui, K. Schaefer, and D. Conrad, Dec. 14, 2016.  California, Flood Risk, and the National Flood Insurance Program.  California Water Blog, https://californiawaterblog.com/2016/12/14/california-flood-risk-and-the-national-flood-insurance-program/

Pinter, N., 2019.  The Problem with Levees.  Scientific American, Observations (Scientific American Online OpEd), Aug. 1, 2019.  https://blogs.scientificamerican.com/observations/the-problem-with-levees/

Pinter, N., Aug. 28, 2013.  The New Flood Insurance Disaster.  Op-Ed in The New York Times; http://www.nytimes.com/2013/08/29/opinion/the-new-flood-insurance-disaster.html

Schaefer, K., and N. Pinter.  Flood Mapping in California: The Good, the Bad, and the Ugly.  California Water Blog, Jun. 16, 2019.  https://californiawaterblog.com/2019/06/16/flood-mapping-in-california-the-good-the-bad-and-the-ugly/

U.S. Army Corps of Engineers, Sacramento Division, 2021a.  Natomas Basin.  https://www.spk.usace.army.mil/natomas/

U.S. Army Corps of Engineers, Sacramento Division, 2021b.  Reducing Flood Risk in Sacramento.  https://www.spk.usace.army.mil/Missions/Civil-Works/Sacramento-Levee-Upgrades/

U.S. Government Accountability Office (GAO), 2014.  National Flood Insurance Program: Additional Guidance on Building Requirements to Mitigate Agricultural Structures’ Damage in High-Risk Areas Is Needed.  https://www.gao.gov/products/gao-14-583

[1] https://www.spk.usace.army.mil/natomas/

[2] https://www.spk.usace.army.mil/Missions/Civil-Works/Sacramento-Levee-Upgrades/

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Could California weather a mega-drought?

Source: National Resource Conservation Administration
Source: National Resource Conservation Administration

By Jay Lund

“Mega-drought” has become a frightful “thing” in public and media discussions.  In the past 1,200 years, California had two droughts lasting 120-200 years, “megadroughts” by any standard. Could the state’s water resources continue to supply enough water to drink, grow crops and provide habitat for fish with such an extreme, prolonged drought today?

Clearly, some ecosystems and rural communities would be devastated by such a drought, and it would certainly affect all California residents.  But with careful management, California’s economy in many ways could substantially withstand such a severe drought.

The UC Davis Center for Watershed Sciences explored this question a few years ago using computer models. We constructed a drought similar in scale to the two extreme ones found in California’s geological and biological records of the past 1,200 years (Harou, et al. 2010). We created a virtual 72-year-long drought with streamflow at 50 percent of current average rates, with all years being dry, as seen in the paleo-drought record.

We then explored the simulated drought using a computer model of California water management that suggests ways to minimize the economic costs of water scarcity for populations and land use in the year 2020.

Not surprisingly, the model results showed that such an extreme drought would severely burden the agriculture industry and fish and wildlife, and be catastrophic to some ecosystems and rural towns. The greatest impacts would be felt in the Central Valley.

However, if well managed, such a mega-drought would cause surprisingly little damage to California’s economy overall, with a statewide cost of only a few billion dollars a year out of a $2+ trillion-a-year economy.

The key to surviving such a drought lies in adaptive strategies such as water trading and other forms of water reallocation. These strategies would be essential to improving the flexibility of California’s water supply and demand system during such a prolonged drought.

Interestingly, most reservoirs we have today would never (yes, NEVER) fill during a decades-long drought.  So expanding surface storage capacity for managing megadroughts would be futile.

California has a very flexible water supply system that can support a large population and economy under extreme adverse circumstances — provided it is well managed.

In adapting to the climate warming and changes that are upon us, the most important thing for California is to be well-organized and led for effective water management.  Panic or complacency generally lead to poor decision.  Good management of such a complex system will require serious and reasoned analysis and discussions, plus a political will to make reasoned decisions, even when ideal solutions do not exist.

Jay Lund is a professor of civil and environmental engineering and co-director of the Center for Watershed Sciences at UC Davis.

This article originally ran April 12, 2011. Some text has been updated,

Further reading

Harou, J. J., J. Medellín‐Azuara, T. Zhu, S. K. Tanaka, J. R. Lund, S. Stine, M. A. Olivares, and M. W. Jenkins (2010), Economic consequences of optimized water management for a prolonged, severe drought in California, Water Resources Research46, W05522, doi:10.1029/2008WR007681.

MacDonald, G.M. (2007), Severe and sustained drought in southern California and the West: Present conditions and insights from the past on causes and impactsQuaternary International, 173-174: 87-100.

Stine, S. (1994), Extreme and persistent drought in California and Patagonia during medieval timeNature, 369, 546–549, doi:10.1038/369546a0.

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