Two-Thirds of California Completely Drought-Free as 'Big Melt' Begins

Drought-stricken California is in for another break, with the snowpack in the Sierra Nevada about to start melting with rising springtime temperatures.

Over two-thirds of the state is now completely free of any drought conditions, according to U.S. Drought Monitor data, which is a stark change from the mere 0.64 of the state that was drought-free only three months ago, on January 24.

The U.S. Drought Monitor shows that as of April 25, 68.04 percent of California is drought-free, while 23.98 percent is still "abnormally dry" and 7.98 percent is in "moderate drought." Last week, on April 18, 65.67 percent of the state was drought-free. In mid-March, only 44.66 percent of California was drought-free, and only a week before, on March 7, 26.84 percent was drought-free.

Even more of the state is expected to climb out of drought conditions with the melting of the snowpack, thanks to California's increasing temperatures.

This year, multiple atmospheric river storms have battered California, causing large amounts of rainfall in the lower levels and record-breaking snowpack in the Sierra Nevada.

On March 13, California Department of Water Resources data showed that the Southern Sierra—ranging from San Joaquin and Mono counties to Kern County—had a snowpack 257 percent greater than the average for that date. This broke the record for the most snow for that time of year, which occurred in the 1982-1983 season.

The rainfall helped alleviate the state's drought. At the end of last year, on December 27, 28.33 percent of California was under the Drought Monitor's most severe condition, "exceptional drought." In the coming weeks, however, California is set to be inundated with meltwater from the snowpack, in what has been dubbed the "big melt."

"The big melt is now here," Daniel Swain, a climate scientist at UCLA and the National Center for Atmospheric Research, said in an online "office hours" session streamed on YouTube. "This week is going to be an exclamation point on the warming process."

He continued: "We said there would eventually be some week between about March and May when the rate of snowmelt dramatically increased, either due to a heat wave or late-season warm storm. I think this is probably that week now."

As snow in the Sierra Nevada melts and flows down the mountains into the valleys, it fills the empty reservoirs. However, if too much water descends at once, this can cause flooding. The recent record-breaking snowpack is thought to pose a flooding risk for the Tulare Lake Basin and the San Joaquin River Basin, with flooding having already hit the Central Valley.

Jacob Petersen-Perlman, a water resources geography expert and assistant professor at East Carolina University, previously told Newsweek: "Timing also matters. All the rain at once means that much of it will run off into the ocean instead of filling California's reservoirs."

The National Weather Service has forecast that the Merced River could reach 12.5 feet during the first week of May, which is over the 10-foot limit at which the river reaches a flooding level.

These conditions are exacerbated by the fact that California's soil is parched after years of megadrought, which means that the soil struggles to absorb the water, causing it to run over the ground's surface.

This also means that the water will only help somewhat to fully pull the state out of drought, as the depleted groundwater stores across the state will not be refilled.

"Over the last 25 years, we have lost more than 150 [cubic kilometers, or 121,600,000 acre-feet] of groundwater from California, which would take many, many years of rain to replace, even if there were no consumptive use for municipal or agricultural purposes," Aakash Ahamed, a hydrologist and co-founder of the Water Data Lab, told Newsweek in October last year.

For the state to be totally cured of drought, several years of large rainfall like this one are needed to replenish the groundwater stores.

"It will take several years of above-normal precipitation—both rain and snow during the appropriate times of the year," Lara Fowler, an environmental and energy issues attorney and interim director of the Penn State Sustainability Institute at Penn State University, previously told Newsweek.

She continued: "As soil moisture and surface water supplies have become depleted, more and more groundwater pumping has also led to a decline in aquifer levels in many places. Such groundwater contributes to baseflows in streams. So not only would surface water [streams and rivers] need to refill, so does soil moisture and groundwater levels, the last of which can be very slow to recharge."

Do you have a tip on a science story that Newsweek should be covering? Do you have a question about California's big melt? Let us know via science@newsweek.com.