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Huge California storm not enough to rescue state from drought

The category 5 atmospheric river was important to California’s water picture, but if the drought is to be assuaged, more storms will have to march through the region during the upcoming winter.

(CN) — The atmospheric river that broadsided Northern California was one of the most powerful for any time of year in recent memory, yet even the voluminous amounts of precipitation that fell on the state were insufficient to break the spell of drought, according to a new report released Thursday. 

The Center for Western Weather and Water Extremes, which tracks the severity of atmospheric rivers in the American West, said the one that hit San Francisco and the rest of Northern California beginning Sunday and continuing into Monday, was a category 5, the strongest category. 

However, that storm, while helpful in terms of ending fire season in Northern California early and making a dent in the drought, was not able to put the American West back on quality footing as it relates to water supply. 

The U.S. Drought Monitor released its weekly report Thursday and found that 100% of California is mired in drought, categorized from moderate to exceptional, the worst category. Exceptional drought still covers about 39% of the state, down incrementally from the week previous to the storm, when about 46% of the state was plagued by exceptional drought. 

“While this AR and recent smaller storms improved drought conditions, they did not come close to ending the drought,” said the authors of a report published by the National Integrated Drought Information System on Thursday. “The current drought developed over many months to years and has persisted, in some parts of the West, since early 2020.”

In California, many of the reservoirs were replenished by the rain, and Lake Tahoe set a record by rising six inches in a single day, an unprecedented feat. However, several of the reservoirs remain below historical averages

Shasta, the largest reservoir in the state, remains at 22% of its capacity, which is about 41% of historical average for this time of year, despite the deluge earlier in the week. Oroville is also at 53% of its historical average and several other major reservoirs are well below normal levels. 

Lake Oroville for example rose ~170,000 acre feet from these storms but to get to median levels for this time of year, when reservoirs are typically the lowest levels for the year, needs yet another million acre feet,” the report reads. 

The report argues that only above normal precipitation throughout the winter season in the American West will restore the water picture to a more sustainable place. The California Department of Water Resources recently said that the state would have to enjoy 140% of a normal water year in order to get most places back to average in terms of soil moisture content, underground water aquifer levels and reservoir system health. 

“Large precipitation deficits remain,” the report says. 

Furthermore, the type of precipitation is important. The state of California in particular, is reliant on large snowpacks in the Sierra Nevada, where the water can melt off incrementally, replenishing the reservoirs throughout the late spring and early summer. 

If most of the rain falls as rain instead of snow due to higher temperatures in the upper elevations, it doesn’t have the same beneficial impact as storms that construct a more robust snowpack. 

Some have said the storm in October portends a wet winter for California and the rest of the American West, but forecasters are quick to say that early season storms, regardless of strength, are an unreliable indicator of how the rest of the water year will develop. 

“This is a pretty strong event for so early into the season, but in general, it is not a strong signal one way or the other,” said Sean Miller, a forecaster with the National Weather Service. 

Thursday’s report from the drought information system stressed more storms with copious precipitation, preferable that manifest as snow at upper elevations in the Sierra, are necessary to truly allay concerns about drought in California and other areas of the American West. 

“Relief or intensification of drought along the west coast and inland will depend on the frequency, strength, and trajectory of storms,” the report states. 

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