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Mammoth Mountain received record snowfall in May 2019. Photo: Mammoth Mountain, Inc. California Reservoirs

Water Year 2020 Begins With Robust Reservoir Storage

Last winter was a bountiful one in terms of water supply for California, but it’s still too early to tell whether 2020 will be as generous.

The 2018-19 winter was one for the record books, with above-average precipitation. Snow continued to fall in late-spring, with several inches or more in the Sierra Nevada and the Southern California mountains.

Ski seasons were extended into May and June, delighting skiers and resort operators.

The snowfall, and a boost from late-season storms, increased the northern Sierra snowpack in May 2019, which was “atypical,” according to Alexi Schnell, water resources specialist with the San Diego County Water Authority.

The statewide Sierra Nevada snowpack was 164% of normal, with the northern Sierra at 172% of normal on May 23, 2019.

Major California Reservoirs Above Historical Average on November 8, 2019

Most major California reservoirs are above their historical averages as of November 8, 2019. (Graphic: California DWR)

Water Year 2020 begins with robust reservoir storage

The 2019 water year (October 1 – September 30) pushed snowpack levels well-above average and swelled major reservoirs to above-average. There were more than 30 atmospheric rivers, with many making landfall in Northern California. The state’s snowpack on April 1 was 175% of average.

The California Department of Water Resources said that makes a great start to 2020.

“We start the new water year in a good place,” said Karla Nemeth, director of the DWR. “However, we all know too well that California’s weather and precipitation are highly variable. What we have today could be gone tomorrow.”

Above average rainfall in San Diego

While the biggest gains in precipitation over the past year were in Northern California, the San Diego region also benefited. Water Year 2019 ended with the region at 125% of average rainfall at Lindbergh Field. The rainfall helped increase supplies in regional reservoirs.

Schnell cautioned that the climatological cycle in California can bring several consecutive years of drought, like the 2015-17 period, which prompted mandatory water-use reductions statewide.

Above-average temperatures in California in 2019

NOAA reported on November 6 that California experienced above-average to much-above-average temperatures from January through October 2019. The average U.S. temperature during that same period was 55.5°F, (0.5 of a degree above 20th-century average) “ranking in the warmest third of the record,” according to NOAA.

NOAA reported that California has had above-to much-above-average temperatures from January to October 2019.

NOAA reported that California has had above-to much-above-average temperatures from January to October 2019. (Graphic: NOAA)

Scripps Institution of Oceanography’s Center for Western Weather and Water Extremes, or CW3E, just released an analysis that calculated the odds of water year 2020 reaching 100% of water year normal precipitation totals. The odds range from 20 to 40% of the Southwest reaching 100% of water year normal precipitation.

Odds of reaching normal precipitation for Water Year 2020. (Graphic: CW3E, Scripps, UC San Diego)

National Weather Service seasonal outlook for precipitation

The three-month seasonal precipitation outlook for November-December-January by the National Weather Service Climate Prediction Center shows below-normal to normal precipitation in Central to Northern California and equal chances of below, near- or above-normal in southern California and much of the Southwest.

The November-December-January precipitation outlook from the National Weather Service.

The November-December-January precipitation outlook from the National Weather Service. (Graphic: NWS/NOAA)

“There will always be fluctuations based on weather and other factors, but the San Diego region continues to embrace water-use efficiency,” said Schnell. “The Water Authority and its 24 member agencies continue to increase San Diego County’s water supply reliability through supply diversification to provide a safe, reliable water supply to the region.”

2019 Water Year Sees Above-Average Rainfall

After a lackluster amount of rainfall throughout the San Joaquin Valley in 2018, the recent end to the 2019 precipitation year was a welcome sight for community members wary of drought thanks to plenty of storms that brought above-average numbers.

This past precipitation year, which began Sept. 1, 2018 and ended Aug. 31, 2019, saw 45.65 inches of rainfall — nearly 10 inches more than the historical average for the area or about 125 percent of average for the date.

Water Year 2019 Leaves Reservoirs With Good Storage

As water years go, 2019 was all wet. With the new water year beginning Oct. 1, farmers and forecasters hope for more of the same. Tulare County farmer Zack Stuller described 2019 as a “fantastic year” for water.

As a result of the atmospheric river weather phenomenon, California has experienced higher than average rainfall in water year 2019. Graphic: National Weather Service

Atmospheric Rivers Benefit State, Regional Water Supply

Atmospheric river events in late January and in February have significantly increased snowpack in the Sierra Nevada and the Rocky Mountains, key sources of water supply for the state and San Diego County.

“We’re thrilled by the amount of precipitation – rain and snow – in San Diego County, the Sierra and the Rockies,” said Dana Friehauf, a resource manager with the San Diego County Water Authority.

The statewide Sierra Nevada snowpack was 151 percent of normal at 104 reporting stations for February 27, according to the California Department of Water Resources. The Rockies have received significant snowfall, which will feed the Colorado River, a source of water supply for the Water Authority. The amount of precipitation in most of the Rocky Mountain region, has ranged from 100 to 150 percent for Water Year 2019 through February 25, according to data from the Natural Resources Conservation Service. The percentage is based on the median between 1981 and 2010.

As a result of the atmospheric river weather phenomenon, California has experienced higher than average rainfall in water year 2019. Graphic: National Weather Service

As a result of the atmospheric river weather phenomenon, California has experienced higher than average rainfall in water year 2019. Graphic: National Weather Service

Record rainfall recorded in San Diego

Locally, a bountiful February has helped make Water Year 2019 one of the wettest on record at Lindbergh Field. Preliminary data from the National Weather Service indicates 10.62 inches of precipitation at the San Diego International Airport, with 3.42 inches coming so far in February 2019.

The Weather Service report issued Feb. 24 also shows that last year at this time, just 1.91 inches of precipitation had been recorded at the airport (for Water Year 2018).

In fact, Water Year 2018 (October 1 – September 30) was the second-driest on record since 1850 at Lindbergh Field, with just 3.3 inches of rain, or 32 percent of the long-term average.

Friehauf reminds San Diegans that even in years such as this, when rainfall is plentiful, that water-use efficiency remains a way of life. For instance, each rainstorm is an opportunity to turn off irrigation systems for days or even weeks at a time. She also suggests residents use rain barrels to collect or “harvest” water that can be used later, when the weather is drier.

Capturing the water from gutters and downspouts also reduces the amount of water flowing into storm drains. Homeowners can get rebates on residential rain barrels. Find details on rain barrel rebates here.