Natalie Hanson

SACRAMENTO, Calif. (CN) — In what is expected to be one of the biggest snowmelt events in its history, California could see some 277 billion gallons of water flowing from the Sierra during the month of May alone.

Experts said Tuesday that the state's biggest snow year since 1950 could result in a dangerous spring, as warming temperatures push high volumes of snowmelt downstream. The season’s penultimate snow survey conducted one week ago found the Phillips Station snow course, one of more than 260 courses across the Sierra Nevada measured every winter and spring, has a snow-water content of 54 inches, or 221% of the April 1 average. The statewide augmented sensory network reported snow levels are at 237% of average.

California Department of Water Resources climatologist Michael Anderson said in a briefing Tuesday that the biggest snowmelt flows are expected in the southern Central Valley, including areas like Kings and Tulare counties that have been badly affected by drought.

“How this plays out will depend on the weather, and how quickly we warm up,” Anderson said. While Monday marked the warmest day of the year so far, temperatures will gradually cool by Friday, a pattern he said should repeat throughout April.

“We expect most of the runoff to come in May," the department’s hydrology branch manager David Rizzardo said. But he noted that each big water year is very different, and the “timing, pace and scale” of previous storms will affect water management responses.

The department’s director Karla Nemeth has said Californians need to be ready for fast, cold and dangerous river flows as the record snowpack melts. The unprecedented rapid succession of atmospheric river storms has already prompted declarations of emergency in 47 counties across the state since February.

Governor Gavin Newsom last week announced that the White House approved California’s request for a presidential major disaster declaration, to support the state’s emergency recovery efforts and secure resources for affected residents. The declaration helps Californians access supports like funding and housing assistance, food aid and medical and legal services. It also includes public assistance to help state, tribal and local governments with ongoing emergency response, recovery costs and hazard mitigation.

Newsom also said that the California Department of Social Services is mobilizing funds from the state Rapid Response Fund to provide disaster recovery services to immigrant Californians impacted by floods.

The department’s Flood Management Division manager Jeremy Arrich said Tuesday that the southern Central Valley is of key concern to flood responders, as flows could inundate the region in coming weeks.

He and U.S. Army Corps of Engineers’ water management chief Jenny Fromm emphasized the tenuous balancing act of using reservoir management to mitigate damaging effects while ensuring groundwater recharge. Unlike surface reservoirs, groundwater basins take months to refill as water from storms and snowmelt slowly makes its way underground.

Fromm said from April through July, reservoir operations will balance releasing snowmelt flows while trying to fill State Water Project reservoirs, in order to prevent damaging larger releases downstream later in the season.

While noting that “we don’t actually know how it’s going to melt,” she said the state anticipates releases near or at channel capacity, in order to create space to send water to drought-addled reservoirs such as in the Tulare Lake Basin.

“When nature decides to give us a bounty, especially after a really tough three years … the goal is to try to maximize the storage or use of that,” Rizzardo said. He added the state must be careful not to flood areas lacking the proper infrastructure and inundate fields and facilities.

Asked about Central Valley residents’ concerns that the state and federal government did not do enough to repair levees before storms arrived, Arrich said California has invested significantly in flood management infrastructure. But in regions which do not participate in state water programs, it falls on local flood managers to work with state support, he said.

Arrich did not know which areas are most at risk of seeing high flood waters, because he said hydrologic modeling tools are still being developed and “we’re not in a position to predict where water may go.” But people need to watch their local flood response agencies closely, and be prepared for — and heed — flood warnings, he said.

“Yes there’s a lot of snow out there, but there’s a coordinated, very active group looking at the situation and exercising as many options as possible to mitigate the hazard,” Anderson said.