Increasing temperatures increase California flood risk

California was experiencing a series of major rain and snow storms in January when Gov. Gavin Newsom proposed a 2023-24 state budget.

Tucked into one of the budget’s hundreds of pages of detail was this paragraph:

“San Joaquin Valley Flood Plain Restoration – A reduction of $40 million General Fund in 2023-24, which eliminates funding for this purpose.”

The $40 million had been a small down payment on the billions of dollars that would be needed to protect communities in the valley from disastrous floods that scientists had been warning could occur under certain meteorological circumstances.

Just last summer, with California still experiencing a years-long drought, a major study warned about the state’s vulnerability to a huge flood similar to one that occurred in 1862.

“We find that climate change has already increased the risk of a (1862) megaflood scenario in California, but that future climate warming will likely bring about even sharper risk increases,” the study declared.

Researchers Xingying Huang and Daniel Swain, a UCLA climate scientist, said such an event “would likely produce widespread, catastrophic flooding and subsequently lead to the displacement of millions of people, the long-term closure of critical transportation corridors and ultimately to nearly $1 trillion in overall economic losses.”

In a rational world, the warning would have moved state officials to hurriedly plan the bypass channels, floodplain improvements and other public works to mitigate the threat. But it was largely met with indifference.

Thus, Newsom and his budget advisors considered the $40 million to be expendable as they tried to adjust spending to match sharp reductions in revenue. However, they managed to protect, or even expand, other expenditures for items with much less importance, such as $1.5 billion over five years to subsidize the politically influential film industry.

The $40 million cut drew catcalls from San Joaquin Valley legislators, and the money may be restored in the final budget. Nevertheless, it symbolizes long-running political disinterest in the looming threat of devastating floods – one that could become reality later this spring.

The Tulare Lake basin between Fresno and Bakersfield is already experiencing heavy flooding as the weather warms and the record-high Sierra snowpack releases its immense amounts of water. Tulare Lake was once the largest body of freshwater west of the Mississippi River, but dried up as its tributaries were diverted by dams. However, every few decades the lake reappears when runoff overwhelms the capacity of those dams.

This year is an especially worrisome example of Tulare Lake’s re-emergence because of the truly epic amounts of snow in mountains that loom to the east of the basin, as much as 400% of the historic average.

The state Department of Water Resources recently calculated that the watersheds of four rivers feeding into the lake will release more than 6 million acre-feet of water by July, several times the capacity of the rivers’ reservoirs, even if they were empty. Dam managers are trying to draw down their reservoirs by releasing more water into Tulare Lake to provide a buffer, but a rapid melt could easily overcome them.

While the situation in the Tulare Lake basin is especially perilous, it’s not the only region at risk. The state expects more than 10 million acre-feet of water to flow through the Sacramento River system by July and another 10 million through the San Joaquin River.

What happens to inland California in the next few months will largely depend on the weather. A cool spring and early summer might allow these prodigious amounts of water to be managed with little or no additional damage. But a prolonged heat wave could mean disaster for some communities.