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OAKLAND, Calif. October 7, 2020 — Water managers are underprepared for climate change in ways that will leave the state simultaneously at increased risk of water shortages and floods, according to a new analysis released today by the Union of Concerned Scientists (UCS) and accompanying peer-reviewed study in Climatic Change. The volatile swings from very dry to very wet years will become more intense and more frequent by late century as the climate changes. The state experienced exactly this scenario in 2017 and 2018 when bone-dry drought parched the state and left thousands without drinking water then was followed by lethal flooding and mudslides that overwhelmed communities like Santa Barbara and broke Oroville Dam’s spillways.

The UCS study analyzed climate model projections that were developed for the 4th California Climate Assessment and are widely used in state climate planning and guidance documents. The analysis, which looked at where the models’ findings converged, uncovered a troubling picture for California’s water future.

The study found the top ten climate models used by the state government agree there will be nearly complete snowpack loss at lower elevations statewide by the end of the century, if heat-trapping emissions continue to rise as currently expected. The models agree that almost the entire state will struggle with shorter, wetter winters and longer, drier summers and experience many more very wet and very dry years. The expected changes in the length, intensity and volatility of wet seasons, coupled with a dramatically diminished snowpack will, by late century, reduce water supply and require greater and more flexible water storage, including restoration and sustainable use of groundwater aquifers, than currently exists.

The report points out that these predicted climate changes have been overlooked by water managers.

“Water managers have been overly focused for years on the question of how much more or less precipitation we’re going to get because of climate change,” said Geeta Persad, lead author of the report, and assistant professor of climate science at The University of Texas at Austin who authored the report while working as a senior climate scientist at UCS. “This analysis shows that what managers should be asking is not only ‘how much rain or snow will fall,’ but also, ‘how volatile will water flows be from one year to the next?’ and ‘can our water storage systems handle more extremes year after year?’”

According to the study, the frequency of swings between very wet and very dry years will double or triple across most of the state by the end of the century, increasing year-to-year volatility and potentially contributing to fatal mudslides, unexpected wildfire behavior and damage to water infrastructure. That situation could be made worse if the up to 20 percent increase in more extreme precipitation events that create dangerous flood conditions and hard-to-manage flows into reservoirs does occur as predicted by more than 80 percent of the state’s best climate models.

“Collectively, these findings have significant implications for everything from wildfire risk to groundwater sustainability to flood insurance policies,” said Daniel Swain, co-author of the report, and climate scientist at the University of California Los Angeles Institute of the Environment and Sustainability. “The findings also suggest that decision makers and water managers may find greater consistency in climate projections by looking beyond average conditions, and focusing specifically upon the extreme drought and flood events that are most likely to stress water systems and infrastructure in the first place.”

Rural communities throughout the state will bear the burden of the state’s slow action on climate change, according to the report, which pointed out that rural communities have less capacity to plan and adapt without state data and guidance. Communities, such as those in the San Joaquin Valley, have fewer water supply options, are located in areas more likely to flood and experience extreme heat, struggle with badly managed water systems, have less capacity to do their own climate risk planning, and often suffer from poor water quality.

“Climate change will worsen the inequities for thousands of Californians who already are at increased risk of flooding or without access to clean, drinking water,” said José Pablo Ortiz Partida, climate scientist at UCS and co-author of the study. “Water managers must do more to plan for climate change. We know enough about what to expect to start planning differently now.”

The report called for the state to prioritize climate planning across its water decisions. The state can improve the water system’s climate readiness by protecting aquifers and maximizing water managers’ ability to store water underground.

“By shifting its reliance from the dwindling snowpack to well-managed use of its massive groundwater aquifers, water managers will be better able to handle the large volumes of rainfall and snowmelt that, because of climate change, are expected to fall in shorter amounts of time,” said Persad.

In addition, water managers should start thinking about how to operate the system of dams, surface reservoirs, pipelines, tunnels and canals differently. The report recommended the state create guidelines based on future projections rather than historical data to ensure managers make better decisions about when water is released or stored.

“Without a fundamental shift in how our water is managed, we are at risk of supply shortfalls, more damage to our infrastructure, dangerous flooding, and millions of dollars in wasted investments,” said Adrienne Alvord, Western States director at UCS. “It can take years to make changes in how we allocate water and decades to upgrade or build new infrastructure. Federal, state and local water managers’ misdirected focus is wasting precious time we need to overhaul our water system, our water laws and our processes. State leaders must plan now because climate change is altering everything related to California water.”

The Union of Concerned Scientists puts rigorous, independent science to work to solve our planet’s most pressing problems. Joining with people across the country, we combine technical analysis and effective advocacy to create innovative, practical solutions for a healthy, safe and sustainable future. For more information, go to www.ucsusa.org.