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How do California storms compare to the big ones in history?

by SuperiorInvest

Storms that have battered California since last month have left many communities scrambling to clean up and dig out of flooding and mudslides. However, according to one indicator, the state saw it much worse.

Cumulative precipitation this winter in California is well above the 70-year average, according to the National Oceanic and Atmospheric Administration. But at this point in the season, it’s not as high as it has been in some years, including 2017, when there were heavy thunderstorms almost caused a catastrophic collapse at Oroville Dam in northern California.

The data is a reminder that nature has even more to offer the state than it has this season, though there’s still plenty of time for more storms to roll through before drier months. (These precipitation levels include both rain and snow. The latter is recorded as the equivalent liquid amount.)

A nationally averaged measurement like this doesn’t capture the vastly different effects California storms, driven by atmospheric rivers, can have in different parts of the state. A system that brings misery and destruction to Southern California may seem tame in Northern California, and vice versa. The same weather can plague one place but spare the next, which is part of what makes thunderstorms difficult for meteorologists to predict.

“It only takes a very small change in the angle or position of the atmospheric river and a completely different basin will be flooded,” said David A. Lavers, an expert on atmospheric rivers at the European Center for Medium-Term Weather. Forecasts in Reading, England.

Timing is also important. A very intense burst of back-to-back storms like last month’s can cause massive damage in a water year that would otherwise end up on the dry side. The steepness of the lines on this chart can matter as much as how high they end up.

According to NOAA data, the water year that ended up being the wettest since the 1950s was between 1982 and 1983. Wild storms washed away homes and structures along the Southern California coast in January 1983. Another misery came that marchincluding cases a a tornado cut through Los Angeles.

Another water year that stands out in the data is 1996-97. Around New Year’s, rain from a strong atmospheric river breached levees and flooded cities and highways, particularly in the Sacramento and Central Valleys. Damage from this event exceeded $3 billion, according to the study led by Thomas W. Corringham, a Scripps Institution of Oceanography researcher at the University of California, San Diego who specializes in the economic and social impacts of extreme weather.

The NOAA data also highlights how exceptionally dry some recent periods have been, particularly the two water years from 2019 to 2021. Water and soil conditions before each rainy season, and even before each storm, play a large role in shaping the severity of the effects. will be.

“Throughout the year, we’ve had a year-round precipitation deficit,” said Jan Null, a meteorologist formerly with the National Weather Service in California. Had the main reservoirs not been so empty before the rains started last month, the flooding around San Francisco and other areas could have been worse, he said.

This drought also means the recent rain and snow could go further towards replenishment California Water Resources. After the atmospheric rivers of this month, an precipitation index in the northern Sierra Nevada was on pace to match some of the wettest years on record. This index is closely watched because it reflects rainfall levels in the watersheds that feed several of the state’s most important reservoirs.

What a difference it makes to the state water woes it depends partly on how the rest of the season plays out. Previous California winters had a wet start, but then suddenly dried up like a faucet turned off in the sky. “If we stop now, most places will be back to normal,” Mr Null said.

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