California’s deepening drought has worsened into a crisis, as a second dry year in a row has diminished the state’s water supply and another difficult fire season looks inevitable. Nearly three-quarters of the state is in extreme to exceptional drought. With the wet season all but over and a hot, dry summer probably ahead, water shortages and fire danger are poised to intensify.

The past several weeks have shown dramatic change in drought status: Extreme drought has expanded through the northern Sierra’s crucial water region and in the agricultural San Joaquin Valley.

Exceptional drought, the worst category in the federal government’s U.S. Drought Monitor, has descended upon the Bay Area and the nearly snow-free southern Sierra. Moderate drought conditions or worse cover all of California.

Cindy Matthews, senior hydrologist with the National Weather Service’s Sacramento office, said the recent drought progression is a result of the dry winter, which has been followed by a very warm and dry spring. Most of the state has received less than a half-inch of rain since April 1.

[Drought-plagued California and western U.S. may see another devastating fire season]

California Gov. Gavin Newsom (D) has declared a drought emergency in 41 counties, a move that will help to conserve water in reservoirs, although many sectors will vie for that limited supply downstream, including households, farmers and freshwater ecosystems.

“There is not enough water available, so reservoir operators have reduced their allocations to those who have rights to that water,” Matthews said in an interview. There are reports of farmers allowing fields to go fallow this spring because there probably will not be enough water to sustain some crops through the season. Freshwater fish species such as salmon are also threatened by low stream levels.

The drought is hitting especially hard in the wetter northern half of the state, where major reservoirs are fed by mountain snowmelt. The two largest of those, Lake Shasta and Lake Oroville, are at 46 percent and 40 percent, respectively, of their total capacity this week and are lower than they were at this date during the 2012-2016 drought. Because of climate change, the prolonged dry spells of the past 10 years are much warmer and therefore more severe than those that occurred decades ago.

[California’s rainy season now starts nearly a month later, increasing wildfire risks]

Disappearing snowpack

The state’s snowpack, which represents 30 percent of its water supply, stores water high in the mountains and delivers it to surrounding forests, rivers and eventually to reservoirs, in late spring and summer. Most of the streamflow in the Sierra Nevada region comes directly from snowmelt.

This year, though, an already paltry snowpack has melted off at breakneck speed. And instead of flowing into rivers, much of the meltwater has seeped into parched soil or simply evaporated.

“We saw massive, rapid melt-off of the snowpack at the lower and middle elevations,” Chris Orrock of the California Department of Water Resources said in an interview. Statewide snowpack, which peaked March 25 at 64 percent of average, is only 2 percent of average for the date.

April was exceedingly warm over the Sierra, and the loss of snow and streamflow illustrates how higher temperatures due to climate change can compound the effects of droughts.

There was also simply much less snow available this year. Both the northern and central Sierra are on track to record their third-driest year on record, while the southern Sierra probably will see its driest.

“We’ve lost a whole year of runoff in the water project that supplies water across California,” Orrock said, referring to the State Water Project, a storage and delivery system that serves 27 million Californians and irrigates Central Valley farmland.

Although major cities such as San Francisco have diverse water supply portfolios and can draw from numerous sources and backup supplies, smaller cities rely on their local reservoirs and therefore depend on rain that falls in their local watersheds.

Marin County, just north of San Francisco, draws its water from the Russian River watershed, which sits at the epicenter of the current drought. On Tuesday, the county’s board of supervisors declared a drought emergency and further tightened mandatory water restrictions, such as limiting outdoor sprinkler use, to preserve reservoir storage through the long dry season ahead.

Another challenging fire season underway early

An active fire season is already underway in California, as drought and warm conditions have led to summerlike flammability in May.

Although California has always had highly variable year-to-year precipitation, in the past two decades, dry years have become more frequent, occurring three times more often than wet years. Scientists have found that the southwestern United States has been mired in a “megadrought,” the second-worst such era in the past 1,200 years. These long-term dry periods, which can last decades, are marked by low precipitation, as well as low soil moisture and snowpack.

Increasing temperatures due to climate change have doubled down on the megadrought, meaning more water is being lost to the atmosphere, and more precipitation is falling as rain instead of snow. This warming has also translated into greatly increased wildfire risk.

“It’s obvious we’re seeing smaller amounts of snow, and it’s melting earlier — that’s the big change,” Jeffrey Mount, a senior fellow in water and climate change policy at the Public Policy Institute of California, said in an interview.

Mount described 2011 as an example of a “really good cold wet year” with rushing snowmelt in June. Such years are needed to replenish reservoirs and groundwater, but they’ve been few and far between since 1999.

“We have an elaborate system to store and manage water, but it’s all based on 1950s hydrology — not modern hydrology,” he said. In other words, it was built around a past climate, when wet years were more reliable and less water was lost through evaporation.

“Maybe we’ll get lucky and next year we’ll go into a wet period like we had in the mid-90s, and everything will be great,” he said. “But that’s highly unlikely.”

About this story

U.S. Drought Monitor data was used for May 20. Satellite images of Lake Oroville via ESA Sentinel 2 satellite and fire perimeter data via CalFire. ESA Sentinel 3 imagery was used in the two-month comparison graphic, and California Department of Water Resources for the capacity data. Megadrought analysis provided by PPIC Water Policy Center. Snow water equivalent data via NOAA.