California’s water issues may be complicated. But the rainfall shortage driving the state’s current drought is basic math.
Over the three-year period that ended June 30, most Northern California cities received only about half to two-thirds of their historical average rainfall. And each passing year without soaking winter rains has been steadily drying the state out a little more — further dropping reservoirs, further parching soils and forests, and further depleting groundwater.
“In most places we are missing an entire year of rain over the past three years,” said Jan Null, a meteorologist with Golden Gate Weather Services in Half Moon Bay. “It’s like if you worked three years, but only got paid for two. You are going to be hurting.
“We’re going to need an exceptional year coming up to dig us out of the hole we are in right now,” he added.
From July 1, 2019 to June 30, 2022, San Jose received 19.67 inches of rain. That’s just 49% of the 40.44 inches the city should have received in three average years. San Francisco received 56% of its normal, Oakland 58% and Sacramento 59%.
Southern California hasn’t been as parched. Los Angeles received 77% of its historical average over the past three years. And San Diego did best, with 85% of normal.
But most of the state’s largest reservoirs are in Northern California.
Historically, the rugged forests and mountains of Northern California have received far more, and bigger, winter storms, than the balmy beaches and arid deserts of Southern California. So generations ago, state and federal engineers built huge reservoirs like Shasta, Oroville and Trinity in the northern part of the state to catch winter rains and melting snow and send the water to Central Valley farms and Southern California cities in the summer and fall.
“Not to be provincial, but north of the Tehachapis is the most important place for rainfall in California,” said Null, referring to the Tehachapi Mountains in Los Angeles and Kern counties.
Currently, 97% of California is in a severe drought and 58% is in an extreme drought, the third and fourth most serious out of five categories, according to the U.S. Drought Monitor, a weekly report issued by the federal government and the University of Nebraska.
Nobody knows when it will end.
California’s last drought, from 2012 to 2016, ended with massive storms in 2017 that nearly caused the collapse of Oroville Dam and triggered $100 million in flood damage in downtown San Jose.
Modern weather forecasting is only really accurate out to about 10 days, Null noted.
“Looking out over the next 10 days, there are no drought busters in the forecast over that time,” he joked.
The cumulative impact of the drought is becoming an increasing problem.
In normal years, California cities and farms draw down water in major reservoirs, which then fill up again during winter storms. But in the past three years, the winter rains haven’t been enough to fill the reservoirs in most places.
On Tuesday, the largest, Shasta Lake, near Redding, was just 39% full. The second largest, Oroville, in Butte County, was 48% full.
Less visible are massive groundwater basins across the Central Valley and other areas, which also are in retreat, not being recharged enough each of the past three winters.
“Remember, we’ve had two droughts over the past 10 years,” said Jeffrey Mount, a professor emeritus at UC Davis and senior fellow at the Public Policy Institute of California’s water center. “The 2012-16 drought has now turned into the 2020-2022 drought. The problem is that we are not making it up in between. This has a cascade of big-time consequences. These deficits translate directly into declining groundwater. We are really seeing a bad year, particularly in the Central Valley.”
Mount noted that the environment also is seeing cumulative impacts. Soils are drying out more, trees and other vegetation aren’t being replenished. And streams are running low, harming fish and other wildlife.
Most climate scientists believe wet years will return, Mount noted. But because of hotter temperatures from climate change, water is evaporating more quickly.
“We’re going to see wet periods again,” he said. “But the difference is the change in evaporative demand — this thirst of the atmosphere is here to stay. Our dry years are going to keep being drier.”
The solution, he said: More groundwater storage projects, more stormwater capture, more off-stream storage projects, more conservation.
“The grand challenge is to couple reduced demand with increasing storage,” Mount said. “That’s the big frontier for California — how to store water in wet years. Make hay when the sun shines.”
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