Tag Archive for: Water Year 2020

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La Niña and California’s New Water Year

It’s that time of the year in California, when water managers, climatologists and meteorologists look at the factors that determine what the winter will bring during Water Year 2020-21 (October 1, 2020 – September 30, 2021).

The National Oceanic and Atmospheric Administration recently said that La Niña conditions are present in the tropical Pacific, “with an approximately 85% chance of La Niña lasting through the winter.” Forecasters currently think this La Niña will be on the stronger side. For California, those conditions typically mean a drier winter, with increasingly dry conditions heading into 2021.

Fortunately for the San Diego region, any impacts from La Niña will be lessened because of the region’s development of a diversified water supply portfolio. Following a record number of acres burned from wildfires in 2020, La Niña would only increase fire danger.

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La Niña continues in the tropical Pacific, with an approximately 85% chance of lasting through the winter, according to NOAA’s October 2020 La Niña update. Graphic: NOAA

Water Year 2020

But, whether the forecasts come to fruition, and what that means for California’s water supply, won’t be fully known until next spring. What we know now is that the water year that just ended (October 1, 2019 – September 30, 2020) varied across the state.

While Northern California was mostly dry, parts of Southern California experienced above average precipitation, according to the California Department of Water Resources. The agency said that the water year ended below average and pointed to the impact of climate change on the California’s water supply.

Impacts of climate change

“California is experiencing the impacts of climate change with devastating wildfires, record temperatures, variability in precipitation, and a smaller snowpack,” said DWR Director Karla Nemeth. “We must continue to invest in our infrastructure to prepare the state to cope with more extreme weather for the state’s needs today and in the future.”

For Water Year 2020, a lack of precipitation resulted in a snowpack of just 50% of average on April 1, as measured by the California Cooperative Snow Survey Program, making it the 10th smallest snowpack in California since 1950, according to the DWR. California’s reservoirs received just a third of the water runoff from precipitation and snowmelt that they did during the same time period a year ago.

The wet season got off to a slow start, but a series of storms in late November and early December pushed 2019 precipitation to near or above average in central and southern California, according to Goldy Herbon, San Diego County Water Authority senior water resources specialist.

Driest February on record

“The wet start didn’t last with dry conditions taking hold over most of the state in January, and then most of California experienced its driest February on record,” said Herbon.

While precipitation picked up in March 2020 for Southern California, statewide snowpack in mid-March was only 38% of average.

“The dry north/wet south precipitation pattern continued in March and April, with some locations in Southern California setting many daily precipitation records, San Diego included, as northern California precipitation levels remained below average,” said Herbon.

Water supplies in “excellent shape”

Despite the below average year in northern California, Herbon said statewide water supplies are in “excellent shape” thanks to above average precipitation the previous year and good reservoir storage. DWR reports that statewide reservoir storage through the end of September 2020 was projected to be 93% of average.

In the San Diego region, a wet spring boosted rainfall totals to near or above normal.

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Regional precipitation during Water Year 2020. Graphic: National Weather Service San Diego

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.”

Stored Water Provides Strong Start to Water Year 2020

A year ago, at the start of Water Year (WY) 2019 water storage in the State Water Project’s (SWP) largest reservoir, Lake Oroville, was at just 62 percent of average. Although many of the state’s other large reservoirs were posting better averages, water managers and state and federal agency staff were concerned that California may be headed into another drought.

Whereas the next California drought is not a matter of “if” but rather “when,” the concerns of a year ago have been put to rest for the short-term. California began its WY 2020 on Tuesday with significantly more water in storage than the previous year thanks to above-average snow and precipitation.