Despite several snow-heavy winters in California, the snowpack in the Sierra Nevadas has not managed to cure the state of its dry soils.
NASA satellite data has revealed that the recent major snowfall in California has been insufficient to offset the long-term effects of the megadrought plaguing the western states, according to a new paper in the journal Geophysical Research Letters.
This lack of recovery of the groundwater supplies—despite the large levels of snowfall—is concerning for both agriculture and domestic water use.
Data from the Gravity Recovery and Climate Experiment (GRACE) satellites has revealed that the groundwater supply across the whole Great Basin of the western U.S. has dropped by 16.5 cubic miles in the past 20 years. The data also showed that while snowmelt does help refill this water somewhat, it isn't enough to completely replenish the groundwater levels.
"In years like the 2022-23 winter, I expected that the record amount of snowfall would really help to replenish the groundwater supply," study co-author and University of Maryland earth scientist Dorothy Hall said in a NASA statement. "But overall, the decline continued."
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California and the other states in the southwest have been in the grips of a megadrought since the dawn of the millennium, as a result of climate change. This drought has led to the whittling away of the groundwater in the soil, as well as reservoirs, which are critical sources of water for farming and drinking.
"A megadrought is a drought that lasts two or more decades. The current southwest megadrought started in 1999 and has become the longest drought in U.S. history, and also the most severe in at least 1,200 years," Jonathan Overpeck, dean of environmental studies at the University of Michigan, told Newsweek.
"Whereas previous droughts have been caused mostly by a reduction in precipitation, the ongoing southwest megadrought is as much a product of warming temperatures as decreases in rain and snow. The warming is due to human-caused climate change, which is being driven primarily by the burning of fossil fuels," he said. "The megadrought has had huge impacts on the flows of the major southwest rivers, particularly the Colorado River and the Rio Grande, and is currently the cause of a growing water crisis for the southwest."
It was hoped that the high levels of snow that fell in Sierra Nevada over the past few years would help to replenish this groundwater deficit. The Sierra Nevada snowpack on April 1, 2023, was 232 percent the average for that date, marking the highest level since 1952. Additionally, several years since 2010 have seen above-average levels of snowfall during the winter, including 2017 and 2019.
Unfortunately, this new research revealed that the groundwater across the Great Basin has not recovered after these large snowpacks.
"A major reason for the decline is the upstream water diversion for agriculture and households," Hall said. "As the population increases, so does water use."
"With the ongoing threat of drought, farmers downstream often can't get enough water," Hall said. "The ultimate solution will have to include wiser water management."
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