Extreme weather in California: Prolonged drought and record rain

This week has been one for the California history books.

Battered by a major storm, Sacramento on Sunday logged its wettest day since record-keeping began in the 1800s. Eight days prior, Sacramento broke a different record — the longest dry spell in the city’s history, with 212 days without rain.

It’s a study in contrasts playing out across California. San Francisco, Redding and a handful of other cities have shattered rainfall records in recent days, during a year that has overall been one of the driest and hottest in state history.

Experts say the takeaway from the past few days should not be that the drought is over — the state would need far more rain for that — but that this is a glimpse into the future of California.

The total precipitation that California receives each year is unlikely to change significantly this century, but the state will probably experience longer dry seasons and shorter, but more intense, wet seasons because of global warming, according to a 2018 study in the journal Nature Climate Change.

These bursts of rain can be highly destructive. In the winter of 2016-17, an extreme rainy season in California caused mudslides, the collapse of a major bridge in Big Sur as well as flooding that forced more than 100,000 people near Sacramento to flee their homes.

Though rain is usually welcome in a state prone to drought, downpours immediately after dry spells can be particularly damaging, even deadly.

Droughts parch the land and contribute to more severe fire seasons. So when rain comes, vegetation that would typically hold the soil in place has been either charred or dried out, allowing water to wash the land away.

The deadliest mudflow in recorded California history was in January 2018, when rains slammed a region of Santa Barbara County that had been devastated by a large fire the month before. Mudflows as high as 15 feet carried branches and boulders through Montecito. Twenty-three people were killed.

Already, this week’s storm has led to a debris flow that closed a highway in a region destroyed by the Dixie fire this year. People living close to the burn scars of the Alisal fire, which broke out near Santa Barbara this month, have been issued mandatory evacuation orders.

Scientists call these rapid shifts from extreme dry to extreme wet conditions “precipitation whiplash.” And by the end of the century, such events are expected to increase in frequency by 25% in Northern California and to double in Southern California, the study found.

As Daniel Swain, a climate scientist at the University of California, Los Angeles, and the study’s lead author, wrote on Twitter this week: “It is worth noting that this exact situation — an extremely strong atmospheric river bringing brief period of record rainfall in midst of severe and temperature-amplified drought—is what we expect to see in California with #ClimateChange.”

This article originally appeared in The New York Times.

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