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3 Things to Know about California Droughts

Alvar Escriva-Bou April 10, 2018
Shasta Lake

The erratic weather in recent months—a dry winter followed by “atmospheric rivers” that packed a punch in March and April, capped by a poor report on the state’s snowpack—hasn’t exactly offered a clear picture for drought watchers. In fact, there is no universal definition of when a drought begins or ends. Here are three things about droughts that every Californian should know.

Rain, snow, and water in storage are the conditions that define a drought in California.

Technically speaking, a drought is simply having less precipitation than normal. But California’s climate is so variable—indeed, it’s the most variable in the nation—that our “normal” is often either very wet or very dry. We also have an annual, seasonal “drought” from late spring through early fall.

To cope with this variability, we’ve developed a massive storage system and conveyance networks to move water to places where it is scarce and demand is high. Thanks to this elaborate water system, California can face one or two much drier-than-normal years without major disruptions.

California’s mountain snowpack has historically provided “free” seasonal storage for meeting summer irrigation needs. About a third of the state’s annual water supply is stored as snow in the Sierra headwaters. Large reservoirs across the state capture melting snow and release it during our dry summers. Experts have recently begun referring to a new type of drought—“snow drought”—to define years when reduced overall precipitation coincides with unusually warm winters. The winter of 2015 was a good example, with the all-time lowest snowpack in recorded history. Unfortunately, this is becoming more frequent due to the warming climate, and it has big implications for water management because our current system isn’t designed for this shift from snow to rain.

Accounting for these conditions, most of California is not expected to be in a drought this year. Precipitation levels have been low—somewhere between “dry” and “below normal”—and the snowpack is about half of average, but the large reservoirs are still in good shape after the 2017 deluge.

But this might change relatively quickly. As the figure shows, during successive dry years we rapidly draw down storage in reservoirs. By year two or three of a drought, reservoir releases are cut back and water scarcity becomes a problem, particularly in many agricultural regions. Groundwater helps reduce the impacts of drought, but it isn’t sufficient for extended droughts, and significant cutbacks in water use are required.

Drought vulnerability varies across the state.

California suffers a statewide drought only rarely, and the impacts of drought vary. Southern California is a relatively dry region, but it imports half of its water from Northern California and the Colorado River basin, both of which provide more reliable supplies. The central coast, which is not well connected to the statewide water system, relies much more on local precipitation and storage, which means it has a higher vulnerability to drought than other regions. In many areas, groundwater helps offset the loss of surface water during droughts. But long-term overreliance on groundwater—especially in the San Joaquin Valley—has led to negative effects, including dry wells, sinking lands, increased costs of groundwater pumping, and reduced supplies for future droughts.

Planning and preparing for drought can make a big difference. Our research has found that California’s cities and suburbs are the most drought-resilient areas of the state, thanks to significant local and regional investments in diversified water supplies.

Drought is not our only—or biggest—water problem.

Droughts worsen many of California’s water problems and heighten awareness of a number of other issues. But drought is not the underlying cause of critical, chronic problems facing California, such as difficulties accessing safe drinking water, our aquatic ecosystem crisis, or the unsustainable use of groundwater. Perhaps we put too much emphasis on drought―which is, after all, a natural feature of the state’s climate―and not enough on other critical issues.

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