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Wednesday, February 1, 2023

Despite Rain Storms, California Is Still in Drought

A rapid string of punishing storm systems, known as atmospheric rivers, has brought extreme amounts of rain and snow to California during the past weeks, but the sudden deluge has not made up for years of ongoing drought.

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Recent Rains Haven’t Erased Long-Term Drought

Precipitation compared to a 1991-2020 average.

Two maps of California side by side. Left map shows the state mostly in shades of gray and tan, representing below-average precipitation. The map on the right shows the state in shades of teal representing above-average precipitation, with mountain ranges and parts of the central valley in the darkest teal showing 4 times the average amount of rain and snow.


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Short-term view:

Past month

Long-term view:

Past 3 years

Short-term view:

Past month

Long-term view:

Past 3 years

Short-term view:

Past month

Long-term view:

Past 3 years

Short-term view:

Past month

Long-term view:

Past 3 years

Short-term view:

Past month

Long-term view:

Past 3 years

Short-term view:

Past month

Long-term view:

Past 3 years


Source: PRISM Climate Group at Oregon State University

Note: Data from the past six months is preliminary.

The storms inflicted widespread flooding and killed at least 20 people. The onslaught of precipitation also started to refill reservoirs and pile up snowpack in the Sierra Nevada.

Simultaneous flooding and drought are “basically a byproduct of the high variability of California’s climate,” said Jay Lund, co-director of the Center for Watershed Sciences at the University of California, Davis.

The state typically gets its precipitation during the late fall and winter, much of it from storms fueled by atmospheric rivers, and can go long periods of time in the spring and summer without any rain.

California has built its water infrastructure — reservoirs, wells and irrigation systems — in part to account for the imbalanced timing in precipitation. However, the state’s strategy of capturing water during wet periods and reserving it for dry periods gets “more difficult to implement because of the extremes becoming greater” in a warming climate, Dr. Lund said.

The recent rains resulted in a quick and heavy influx of water into many of the state’s reservoirs. Many have returned to or surpassed average levels, but few are at full capacity.


California’s Reservoirs Closer to Recovery

Some reservoir levels are near their historical averages, but below capacity.

Four charts showing reservoir levels within the past year spiking up in recent weeks and either nearing or surpassing historical averages. The larger reservoirs shown are still well below capacity.

Source: California Department of Water Resources

Note: Data as of January 17, 2023 or January 16 where more recent data was not available.

If reservoir levels continue to creep up above average levels, it could alleviate some deficits that have accumulated over consecutive extreme drought years, said Molly White, an operations manager for the California State Water Project.

“It all helps the overall drought picture,” she added.

California has a naturally variable climate: Periods of drought are punctuated by periods of wetter weather. But research suggests that global warming caused by greenhouse gas emissions is making it more likely that any given drought will persist or become more intense, and less likely that any string of wet years will continue.

Climate change will also worsen the wettest extremes. Because warmer air can carry more moisture, atmospheric rivers, which are essentially long plumes of water vapor, will also be able to unleash larger cargoes of precipitation.

The winter is typically the rainy season for California, the time of year when many of the state’s aquifers get recharged with precipitation. But snowmelt that begins in the spring and continues throughout the summer is crucial in refilling aquifers, too, typically providing about 30 percent of the water supply for the state.

The recent storm systems have been the biggest contributor to the snow accumulation in the Sierra Nevada so far this winter. A number of monitoring stations have measured record amounts of snow water equivalent (the amount of liquid water available in snow) for this time of year, reaching seasonal highs usually not seen until late April, when snowpack usually peaks.

On Jan. 17, the recorded snow water equivalent was double what it was last year on the same date, according to data from the California Department of Water Resources.


Storms Build Up California’s Snowpack

Average snowpack levels statewide reached seasonal highs usually not seen until April.

A chart shows average snow water equivalent levels for each water year from 2003 through Jan. 17, 2023. Levels for Jan. 17 are about double what they were last year on the same date.




Previous years since 2003

Previous years since 2003

Previous years since 2003


Atmospheric rivers don’t always bring more snow; storms can actually shrink the snowpack if precipitation falls as rain instead of snow at high elevations. That may happen more frequently as the climate continues to warm.

“Snowpack is in pretty good shape right now,” said Rich Tinker, a meteorologist at the National Weather Service and an author on the latest U.S. Drought Monitor report. “But how it melts is going to be important.” Snow melt usually happens in a slow, stable way, but if temperatures rise quickly, that stability can change, he said.

Last year, an unusually wet early winter ultimately gave way to several dry months that led to restrictions on water use in the summer. Research shows that climate warming and unseasonably warm temperatures in the spring and summer have contributed to an earlier thaw season and more rapid melting.

California’s recent spate of storms will not reverse three years that have been the state’s driest on record. It’s taken multiple years to get to the current state of persistent drought, said Gus Goodbody, a hydrologist at the United States Department of Agriculture’s National Water and Climate Center. “It’s going to be hard for a single season to counteract that.”



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A rapid string of punishing storm systems, known as atmospheric rivers, has brought extreme amounts of rain and snow to California during the past weeks, but the sudden deluge has not made up for years of ongoing drought.


Recent Rains Haven’t Erased Long-Term Drought

Precipitation compared to a 1991-2020 average.

Two maps of California side by side. Left map shows the state mostly in shades of gray and tan, representing below-average precipitation. The map on the right shows the state in shades of teal representing above-average precipitation, with mountain ranges and parts of the central valley in the darkest teal showing 4 times the average amount of rain and snow.





Short-term view:

Past month

Long-term view:

Past 3 years

Short-term view:

Past month

Long-term view:

Past 3 years

Short-term view:

Past month

Long-term view:

Past 3 years

Short-term view:

Past month

Long-term view:

Past 3 years

Short-term view:

Past month

Long-term view:

Past 3 years

Short-term view:

Past month

Long-term view:

Past 3 years


Source: PRISM Climate Group at Oregon State University

Note: Data from the past six months is preliminary.

The storms inflicted widespread flooding and killed at least 20 people. The onslaught of precipitation also started to refill reservoirs and pile up snowpack in the Sierra Nevada.

Simultaneous flooding and drought are “basically a byproduct of the high variability of California’s climate,” said Jay Lund, co-director of the Center for Watershed Sciences at the University of California, Davis.

The state typically gets its precipitation during the late fall and winter, much of it from storms fueled by atmospheric rivers, and can go long periods of time in the spring and summer without any rain.

California has built its water infrastructure — reservoirs, wells and irrigation systems — in part to account for the imbalanced timing in precipitation. However, the state’s strategy of capturing water during wet periods and reserving it for dry periods gets “more difficult to implement because of the extremes becoming greater” in a warming climate, Dr. Lund said.

The recent rains resulted in a quick and heavy influx of water into many of the state’s reservoirs. Many have returned to or surpassed average levels, but few are at full capacity.


California’s Reservoirs Closer to Recovery

Some reservoir levels are near their historical averages, but below capacity.

Four charts showing reservoir levels within the past year spiking up in recent weeks and either nearing or surpassing historical averages. The larger reservoirs shown are still well below capacity.

Source: California Department of Water Resources

Note: Data as of January 17, 2023 or January 16 where more recent data was not available.

If reservoir levels continue to creep up above average levels, it could alleviate some deficits that have accumulated over consecutive extreme drought years, said Molly White, an operations manager for the California State Water Project.

“It all helps the overall drought picture,” she added.

California has a naturally variable climate: Periods of drought are punctuated by periods of wetter weather. But research suggests that global warming caused by greenhouse gas emissions is making it more likely that any given drought will persist or become more intense, and less likely that any string of wet years will continue.

Climate change will also worsen the wettest extremes. Because warmer air can carry more moisture, atmospheric rivers, which are essentially long plumes of water vapor, will also be able to unleash larger cargoes of precipitation.

The winter is typically the rainy season for California, the time of year when many of the state’s aquifers get recharged with precipitation. But snowmelt that begins in the spring and continues throughout the summer is crucial in refilling aquifers, too, typically providing about 30 percent of the water supply for the state.

The recent storm systems have been the biggest contributor to the snow accumulation in the Sierra Nevada so far this winter. A number of monitoring stations have measured record amounts of snow water equivalent (the amount of liquid water available in snow) for this time of year, reaching seasonal highs usually not seen until late April, when snowpack usually peaks.

On Jan. 17, the recorded snow water equivalent was double what it was last year on the same date, according to data from the California Department of Water Resources.


Storms Build Up California’s Snowpack

Average snowpack levels statewide reached seasonal highs usually not seen until April.

A chart shows average snow water equivalent levels for each water year from 2003 through Jan. 17, 2023. Levels for Jan. 17 are about double what they were last year on the same date.




Previous years since 2003

Previous years since 2003

Previous years since 2003


Atmospheric rivers don’t always bring more snow; storms can actually shrink the snowpack if precipitation falls as rain instead of snow at high elevations. That may happen more frequently as the climate continues to warm.

“Snowpack is in pretty good shape right now,” said Rich Tinker, a meteorologist at the National Weather Service and an author on the latest U.S. Drought Monitor report. “But how it melts is going to be important.” Snow melt usually happens in a slow, stable way, but if temperatures rise quickly, that stability can change, he said.

Last year, an unusually wet early winter ultimately gave way to several dry months that led to restrictions on water use in the summer. Research shows that climate warming and unseasonably warm temperatures in the spring and summer have contributed to an earlier thaw season and more rapid melting.

California’s recent spate of storms will not reverse three years that have been the state’s driest on record. It’s taken multiple years to get to the current state of persistent drought, said Gus Goodbody, a hydrologist at the United States Department of Agriculture’s National Water and Climate Center. “It’s going to be hard for a single season to counteract that.”



Source link

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