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Climate whiplash’ is the new normal for California, experts say

Summer is approaching in California, and warmer temperatures have been melting the massive snowpack dumped on the state over the winter. Several swimmers and kayakers drowned this spring as rivers flooded and raged. The National Park Service took the rare step of closing much of Yosemite National Park’s scenic valley for several days to protect hikers and campers from floods. In April, California snowpack was at 237% of the average.

After years of drought, a string of storms over the winter and into the spring dropped as much as 700 inches of snow across California’s mountain range over the winter — even on some beaches. The heavy snowfall caused massive power outages, stranded some mountain community residents for more than a week at a time, and led to at least 13 deaths.

It was a sharp reversal from 2022, when California recorded its driest January, February, and March in over a century and drought records were set across the western U.S. Experts call such wild swings from one type of extreme weather to another “climate whiplash.” And new research shows the trend could worsen and that the wetter years may not make up for extended years of drought. Water managers in the state are already starting to plan strategies to deal with longer droughts and less snow.

After the recent storms, drought maps for the area are looking better in the short term. Yet one year of relief is not a cure. Climate science is shedding light on how precipitation patterns are likely to change as the planet heats up, and recent studies indicate California must prepare for both worsening drought and more intermittent, heavier rainfall.

This year’s onslaught of atmospheric rivers resulted in record snowpack in California’s mountains, where lower temperatures at higher elevations generally lengthen the timetable for melting. In California and many regions globally, snowpack acts as a natural reservoir, slowly melting as temperatures warm in the spring, delivering a steady supply of water to rivers and lakes leading up to the hot, dry summer.

California’s snowpack provides about 30% of California’s drinking water in any given year. The water storage and predictable release of snowmelt are critical for ecosystems and water-management systems, but in an era of climate whiplash, the level and timing of already variable snowpack may become much less reliable from year to year.

A warming climate could make for wetter atmospheric rivers that carry wet air up from the tropics to fall as rain and snow on the West Coast, meaning heavier rain or snowstorms. But changes to seasonal weather patterns around the world could divert atmospheric rivers so they may not arrive on the West Coast as often as they used to.

Scientists have found that climate change has already caused significant decline in mountain snowpacks in many regions, including the Western U.S., and alarming new research projects even larger declines in coming decades. Changes could be more dramatic and occur more rapidly if heat-trapping greenhouse gas emissions continue to increase.

Declining snowpack could have devastating consequences for ecosystems, wildlife, agriculture, livelihoods, and human water security. The good news is this research can serve as motivation to help policymakers and water managers better prepare for futures that will look much different from those of the past.

Changing snow cycles: planning for uncertainty

Across the Northern Hemisphere, the timing of water supplies from snowmelt may shift to earlier in the year, making it harder for water managers to plan for the future, according to findings of research led by Will Wieder, a scientist at the National Center for Atmospheric Research. The study of how climate change would impact seasonal snow cycles in the Northern Hemisphere later this century used a state-of-the-art climate model to evaluate how rising global temperatures would influence snow accumulation and snowmelt in historically snow-dominated mountain areas. The finding is strongly supported by many other studies that find similar shifts across the Western U.S. using both future climate model projections and observed snow measurements.

Another study published last fall in the peer-reviewed research journal Nature Climate Change finds human-caused climate change will fundamentally alter snow cycles in the American Cordillera — the series of mountain ranges that run along western North and South America and include California’s Sierra Nevada. Running sophisticated simulations of the Earth system, the researchers found mountains in the Southern Hemisphere could experience frequent back-to-back years with peak snowpack that is 30% or less than average — in other words, low-to-no snow conditions — as soon as 2046 if the planet is allowed to warm between 2.4°C and 2.9°C above preindustrial levels. 

The results show the low- to no-snow conditions are likely to occur later in the Northern Hemisphere (starting in 2065) in association with a global temperature increase of +3.5 °C, a lag related to the historically warmer temperatures in the southern than in the northern mountain ranges. In both geographies, disappearing snowpack will pose serious risks to water security for the communities that depend on snowmelt for their water supply, and a more rapid rate of warming is tied to snow loss occurring sooner in the coming decades. 

Mountain water runoff will be greater in wet years than dry years, the researchers noted, but will still be diminished because less snowpack increases evaporation. They said that means that wet years will not effectively make up for the dry years as they have done historically, while drier years will be even drier. Worsening the risks, the authors point out, is the fact that water infrastructure has been built based on the historical climate and is not at all prepared for managing heavier intermittent rain or long periods of water scarcity.

Preparing for a low-snow climate future 

The authors of the study of the American Cordillera said their work “highlights the need to implement carbon mitigation strategies at scale.” Planet-heating emissions must be drastically reduced in order to prevent a low- to no-snow worst-case scenario that would dramatically diminish the ability of downstream communities to rely on snowpack for water supply. Even under low-emissions scenarios, snowpack will decline further and has already declined on average. However, snow loss will happen much faster and will be much greater if we don’t start rapidly reducing emissions now.  

Some steps can help California and other snow-dependent regions adapt to a low-snow future. In the Sacramento region, water managers for the 2,140 square-mile American River watershed are rethinking the area’s water infrastructure to prepare for a lot less snow coming from the Sierra Nevada mountains. Already, average monthly storage levels in the Folsom Reservoir, which captures snowmelt and provides drinking water to valley communities, have decreased by 65,000 acre-feet since 2001 from the historical average.

The Regional Water Authority, a consortium of Sacramento-area water agencies, is coordinating a series of integrated water security projects for the 2 million people they serve. This “supershed approach” as they call it, aims to build resilience across the watershed from the mountains to the groundwater in the valley. On the mountain, a forest restoration project is transforming overcrowded forests into a “mosaic of meadows interspersed with thickets of mature trees,” which will not only allow more snow to accumulate on the ground but will also reduce fire risk. 

Water managers are also working together to more effectively use the area’s 1.8 million acre-feet of available underground water storage — more than twice what the Folsom Reservoir can hold. The Sacramento Regional Water Bank will capture excess water during wet years, including surplus flows from the mid-elevation Folsom Reservoir, storing it in underground aquifers to be pumped up during dry years. Water districts will coordinate to ensure surface water from rivers and lakes is shared and primarily relied upon for drinking water during rainy periods, allowing groundwater aquifers to recharge.

In addition to raising the Folsom Dam to allow for greater water storage, water managers are also piloting a new method for operating the Folsom Reservoir called Forecast Informed Reservoir Operations. Traditional rules require reservoir operators to release a certain amount of water ahead of winter to make space for heavy rainfall, helping prevent flooding. If that rainfall does not come, the water is wasted. But advances in forecasting now allow operators to better predict precipitation; they can hold onto water if atmospheric rivers do not come. In a less predictable future, the approach also allows operators to dump more water during a season with unprecedented rainfall.

Sarah Spengeman is the deputy director of communications at Energy Innovation Policy and Technology LLC®. Elise Osenga is a community science manager at Aspen Global Change Institute. Both organizations are Yale Climate Connections content-sharing partners.


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