BERKELEY, Calif. — There is a silver lining to the relentless California storms that have so far killed at least 18 people and racked up an estimated $1 billion in damages: In a single week, extreme drought conditions that had gripped almost one-third of the state have been downgraded nearly everywhere.
The U.S. Drought Monitor released an updated map Thursday that accounts for the series of atmospheric river storms that have doused the state in recent weeks with more than 24 trillion gallons of water. It shows that “extreme drought,” the second-highest classification used by the agency, has been all but erased from the interior sections of the state.
In a single week, the portions of the state classified as experiencing extreme drought in California fell from 27.1% to 0.32%, according to the U.S. Drought Monitor. Still, 46% of the state remains classified in “severe drought,” though that figure fell from 71% a week ago.
Extreme drought conditions are still widespread in Nevada and Utah, and the California storms have not affected the Colorado River Basin, including the badly depleted reservoirs Lake Mead and Lake Powell, where the federal government has been forced to implement water restrictions.
In order to completely eliminate drought conditions across the American West, several consecutive seasons of precipitation at 120% to 200% of normal would need to occur, ABC News reported. A 2022 study published in the journal Nature found that the past 22 years have been the driest period in the Southwest in the last 1,200 years.
As temperatures continue to rise thanks to humankind's burning of fossil fuels, one effect, called the Clausius-Clapeyron relationship, is that there is 7% more moisture in the atmosphere per every degree Celsius of warming. That means extreme downpours, like those in California in recent days, can become more likely when conditions are right. By the same token, however, that relationship can also spur what UCLA climate scientist Daniel Swain has called “flash droughts,” in which extremely dry conditions can arise quickly, even in a year of above-average precipitation.
“The Clausius-Clapeyron relationship also increases what is known as the vapor pressure deficit,” Swain told Yahoo News in November. That means “the atmosphere’s potential to act as a giant sponge and extract more water out of the landscape has increased, even if the relative humidity has stayed the same. This Clausius-Clapeyron relationship is actually what drives the atmosphere’s capacity to dry out the landscape faster.”
For now, however, the precipitation picture is much brighter than it was even a week ago. Water levels in depleted state reservoirs have been rising, and California’s snowpack as of Wednesday measured 226% of normal. While the risks of flash flooding remain high, more rain and snow is in the forecast for the coming week.