Sunday, December 5, 2021

California records driest year in century due to drought

In a year of intense heat and severe drought, California reported its driest year in terms of rainfall in a century, and experts fear the next 12 months could be even worse.

The Western Regional Climate Center added the average rainfall that was recorded at each of its stations and calculated that in 2021, California received a total of 11.87 inches of rain and snow. That’s half of what experts estimate California’s average annual water supply: about 23.58 inches.

The Climate Center calculates rainfall by averaging all measured rainfall in the state at the end of the water year, which runs from October 1 to September 30.

The last water year was the second driest on record, according to the California Department of Water Resources, with decreased rainfall and runoff.

The state last reported such little rain and snowfall in 1924.

Climatologists compared the arid conditions that swept 2020 and 2021 to the 1976-77 drought, which included California’s lowest runoff in one water year.

Average rainfall in 1976-77 was 28.7 inches; in 2020-2021 it was 28.2 inches.

According to a federal report, economic losses from the 1976-77 drought totaled more than $ 1 billion, and some feared the drought could harm the state’s water system.

The current perennial drought has rekindled the same concerns as reservoirs have been depleted and extreme drought announcements have been issued in 50 of California’s 58 counties. Governor Gavin Newsom called on Californians voluntarily reduce water consumption by 15%, and state officials say they could impose mandatory water restrictions if the drought continues this winter.

“California’s history was written during long droughts,” said Bill Patzert, a retired climatologist who spent decades at NASA’s Jet Propulsion Laboratory studying the effects of climate change. “There is a lot of water, but it all depends on how you use it.”

The US Drought Monitor, a weekly map showing drought-related conditions in the US, shows that over 87% of California experiences extreme or extreme drought, with nearly half of the state in the worst category.

Less rain means less water, especially in areas like the Colorado River, an important source of imported water for Southern California.

Lake Mead in Nevada, the main source of water for Los Angeles and the West, has been on the decline since 2000, and the recovery is bleak, experts say. Even if a year of great water comes along, “you won’t even come close to refilling Lake Mead,” said Daniel McAvoy, a climatologist at the Western Regional Climate Center.

All but two of California’s major reservoirs are below average storage levels. Lake Oroville, the state’s second largest reservoir, is at an all-time low. And Lake Shasta, the largest reservoir, is critically low – although not as low as it was in 1977, McAvoy said.

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But unlike 1977, the effects of the drought were exacerbated by accelerated climate change.

The rise in temperature has led to evaporation of precipitation and melting of snow cover much faster than in previous years. according to a recent study by the National Oceanic and Atmospheric Administration

“The high temperatures that helped make this drought so intense and widespread will continue (and increase) until strict climate change mitigation measures are taken and regional warming trends are reversed,” the study said. …

California has had its hottest summer this year and the extreme heat has dried up the landscape.

And as the new water year begins, the state can expect even more. As NOAA reported Thursday, La Niña conditions, which typically bring dry winters to California and the southwest, originated in the Pacific Ocean.

“We already had this dry year, we are in a drought situation, and then there are trends that this winter could potentially be lower than the low rainfall season,” said Jaime Laber, senior hydrologist at the National Weather Service office in Oxnard. … “All of this leads to looking bad.”

NOAA climate scientists predict the current drought will last until 2022 and possibly longer. And while California will become wetter over time, experts say extreme weather changes are needed to bring the state back to normal.

“It will take some time … until we start getting rain and enough rain, when we start replenishing groundwater pools or getting enough rain to see water in our rivers and streams again,” Laber said.

Janine Jones, interstate resource manager for the Department of Water Resources, said the state would need about 140% of the average rainfall to restore the water table.

Rainfall varies across California, and the dry climate of Southern California is very different from the wet and snowy climate of the Sierra Nevada. According to NASA experts, on average three quarters of the state’s precipitation per year falls on Northern and Central California, mainly in the Sierra.

But Southern California has the highest annual rainfall variability in the United States, meaning that any year can fluctuate greatly from wet to arid conditions.

“As scientists think about the long-term effects of climate change, one of the expectations is that this variability will increase,” Jones said. Or, as she likes to say, “the extremes are getting more extreme.”

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