What the onslaught of rain means for California’s drought

California’s immediate drought conditions are being alleviated by the massive amount of rain it has experienced to start the year, but it is not necessarily telling of how it will end.

“We still could have this become a drought year,” said Jay Lund, who helps lead U.C. Davis Center for Watershed Sciences.

That is what happened in 2022, when despite a wet beginning it ended up being the state’s ninth driest year and third straight year in a drought.

Some of the longer-term effects of the rain won’t be clear for months. Scientists will measure the depth of the Sierra Nevada Mountains snowpack on April 1, when it tends to be at its highest point, as an indicator for the amount of water that could flow down from them.

“Typically here in the Sierra, and throughout the western U.S., the April 1 snowpack measurements are the most important because that’s the deepest the snowpack is,” said Andrew Schwartz, lead scientist at the UC Berkeley Central Sierra Snow Lab. “That data is used by water map modelers and managers to determine how much water they’re going to have for the upcoming year.”

As of Thursday, the statewide snowpack for California was 104% of its April 1 average. The National Weather Service said the snowpack was 226% of its average for Jan. 11.

Schwartz said current conditions look good but could change. He said continued cooler temperatures would keep the snow from melting too early in the year and help keep the ground and vegetation moist as the spring and summer months approach.

Beyond the destruction the rain has caused and the ramifications for the drought, officials are watching to see what it will mean for the wildfire season. Ken Pimlott, the former head of the California Department of Forestry and Fire Protection, said moistened ground could delay the onset of peak wildfire season.

In the short term, there has been some slight drought relief. The U.S. Drought Monitor upgraded parts of California, most affected by the drought, to be experiencing severe rather than extreme drought.

Some of the state’s smaller reservoirs are about 80% of capacity, but the larger reservoirs remain relatively low and the overall impact on the drought will depend on the level of precipitation later in the year.

“The reservoirs, as a whole, still are down a bit,” Lund said. “And the groundwater tables are still going to be down a bit in some parts of the state.”

California has been hit by weather systems known as cold atmospheric rivers. They are a river-like collection of water vapor in the sky that comes down as rain and snow as they run into the mountains.

The state is used to these systems and has always gotten much of its water from them, but Schwartz said the warming climate is increasing the amount of water dropped from the atmospheric rivers. “For every one degree Celsius that the atmosphere warms, it can hold 7% more water vapor,” he said.

The state was battered by two atmospheric rivers Friday and struck by six in the preceding days.

Between Dec. 26 and Jan. 11, California averaged 8.61 inches of precipitation and the San Francisco-Oakland metropolitan statistical area averaged 13.34 inches, according to the National Weather Service. San Francisco averages about just over 3 inches of rain during this time period, according to the Washington Post.

Large portions of Central California received over half their normal annual precipitation over that time frame. NWS said the 24-hour period from 4 a.m. on Jan. 9 to 4 a.m. on Jan. 10 ranks as the state’s third wettest one-day period since 2005.

The drought-ravaged soil and vegetation is susceptible to becoming water-logged and contributed to the flooding the state has suffered, said Noah Diffenbaugh, a climate scientist at Stanford.

“We have very dry soils, vegetation that’s been very stressed for extended periods, and then a large sequence of storms — in terms of the number of storms coming in a short amount of time,” Diffenbaugh said. “What that means is that we’re getting a lot of runoff, which is what causes the flooding and mudslides and the sinkholes and impacts that we’ve been seeing.”