Charts show why recent rain in California won’t end drought

California received just more rainfall in the last three months of 2021 than in the previous year. The mountains are blanketed in historic amounts of heavy snow. But as soon as the rain gave way to the sun, state regulators enacted new rules banning water-wasting practices like hosing down sidewalks and driveways. What’s happening?

The short version is that although 33.9 trillion gallons of water has fallen on the state since October 1, that’s not enough to wash away our intractable drought. Here are some graphics to help tell the story.

The latest US Drought Monitor report, released Thursday, shows continued improvement across the west due to heavy rainfall and generous snowpack in mountainous areas. But all of California is still in some degree of drought. And much of the condition remains in the severe or extreme category.

Though many locations in Southern California are near or above 200% of normal precipitation through December, said Jayme Laber, a hydrologist with the National Weather Service in Oxnard, the main stem flows were minimal, and reservoir and groundwater levels are still low.

Most of Southern California’s plentiful rainfall last month washed out into the Pacific, and most reservoirs in the region are low, Laber said. For example, Castaic Lake is about 45.6% full; Lake Piru is only 22.9% full; Lake Casitas is at 34.9%. Jameson Reservoir is the most flush at 66.5%, but it is also one of the smallest reservoirs.

Map of California showing percentage of normal precipitation at various locations

Rainfall is mostly above normal throughout California.

(Paul Duginski/Los Angeles Times)

In Northern California, the key Northern Sierra 8-Station Index was 154% of the average as of Jan. 7, according to the California Department of Water Resources.

The index is the average of eight rainfall measurement sites representing a representative sample of the northern Sierra’s major watersheds. These watersheds include the Sacramento, Feather, Yuba, and American Rivers, which empty into some of California’s largest reservoirs and provide much of the state’s water supply.

The Northern Sierra 8-Station Index on Friday showed 31.2 inches, putting it in the neighborhood of two of the wettest water years on record at this point in the water year: 2016-17 and 1982-83.

The Northern Sierra 8-Station Index as of Jan. 7 is 154 percent of the average

(Paul Duginski/Los Angeles Times)

Major reservoirs fed by rivers in this northern region include Lake Shasta and Lake Oroville. On January 6th, Shasta was only 31% full. Historically, it would have been 52% full on average at this point. Lake Oroville is 40% full compared to an average of 76% at this point.

Luckily for the state’s short-term water supply, the High Sierra stores massive amounts of moisture in cold stores — a kind of snow bank. As it melts in the spring and summer, it will slowly replenish California’s reservoirs. They, in turn, supply water to thirsty communities and farms across the state.

It will likely take at least a few wet years in a row for the reservoirs to fully recover, Laber points out. Because although California has improved greatly in the last 90 days, deficits remain in the long term.

As the US Drought Monitor map for California since 2000 clearly shows, the state has been almost always drought-ridden for the past 22 years. The prolonged dry spell of 2012-2017 includes a period of exceptional drought beginning around 2014; The current dry spell shows an even more abrupt onset of an exceptional drought.

Chart shows sustained, worsening drought conditions in California since 2000 with brief periods of relief

The graphic shows how much and how severely California has been hit by droughts over the past two decades.

(Paul Duginski/Los Angeles Times)

Another way to look at the water situation in California is to look at the map showing the percentage of normal precipitation for the last 24 months instead of just the last three. Though the last three months’ chart celebrates the state’s plentiful recent rainfall, particularly in December, a look at how rain-poor California has been over the past two years is sobering and is guaranteed to put a damper on the party.

The Golden State has experienced below-average rainfall in recent years and is in its second year of La Niña. Typically, La Niña means a dry winter above average, as seen last winter, and the longer-term prospects this year are still generally pointing in that direction.

Maps show abundant precipitation in California since October 1, but deficits for the past two years.

December’s rains kept the water year looking good, but that doesn’t erase the deficits of the last two dry years.

(Paul Duginski/Los Angeles Times)

In addition, the current period of dry years is part of a larger, decade-long drought trend with brief, deceptively wet interludes in California and throughout the West. And all in the context of a warming world where climate extremes are likely to catastrophically intensify.

California’s water situation remains uncertain, and the state is far from out of the drought. To safeguard drinking water supplies, the State Water Resources Control Board enacted rules banning wasteful practices such as washing cars without a shut-off nozzle, over-watering lawns, and hosing down driveways and sidewalks. Violators could face a $500 fine.

A look at these charts makes it clear why the board acted. Charts show why recent rain in California won’t end drought

Tom Vazquez

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