An intense series of storm systems, known as atmospheric rivers, have brought extreme amounts of rain and snow to California in recent weeks, but flash flooding has not been a sign of years of persistent drought.
The storm provoked widespread flooding, killing at least 20 people. Avalanches of rain also began to fill reservoirs and deposit snow in the Sierra Nevada.
Simultaneous floods and droughts “are basically a byproduct of California’s high climate variability,” said Jay Lund, co-director of the University of California Watershed Sciences Center.
The state typically receives its precipitation in late fall and winter, much of it from storms fed by atmospheric rivers, and can go long periods of spring and summer without rain.
California has designed its water infrastructure (reservoirs, wells, and irrigation systems) with erratic rainfall timing in mind. However, the state’s strategy of capturing water during wet periods and reserving it for dry periods becomes “more difficult to implement because of increased extremes” in warmer climates, Lund said.
The recent rains have resulted in rapid and heavy inflow of water into several reservoirs in the state. Many are back at or above average levels, but some are at full potential.
If reservoir levels continue to rise above average levels, it could reduce some of the deficit that has built up during past years of extreme drought, said Molly White, operations manager for the California State Water Project.
“It all helps the overall picture of the drought,” he said.
California has a naturally variable climate: periods of drought are interspersed with periods of wet weather. But research suggests that global warming caused by greenhouse gas emissions makes it more likely that any drought will persist or become more intense, and less likely that a series of wet years will continue.