There are at least two silver linings to be found from Tropical Storm Hilary—the first such storm to hit Southern California in more than 80 years. The first is that, though there were floods, high winds, and dangerous mudslides, no U.S. residents were killed (though one person died in Mexico, where the storm earlier made landfall, according to Mexican authorities). The second is that the torrential rains may have just about stamped out the state’s yearslong drought.
Last year, virtually all of California was experiencing “severe drought,” according to the U.S. Drought Monitor. But the share of California contending with drought conditions has been whittled down to a comparatively small swath of land in Southern California’s interior over the past year, thanks to a series of atmospheric rivers beginning this winter, which piped rainfall across the state and dropped more moisture in the form of gargantuan snowpacks in the Sierra Nevada mountains. A cool spring, meanwhile, meant that that mountain snowpack melted only a little at a time, allowing the state’s water managers to capture runoff in reservoirs. As for that little patch of drought in interior SoCal? It just got walloped by rain from Tropical Storm Hilary.
The main challenge now for California is no longer about getting enough precipitation; it’s about finding somewhere to store all that water, so farmers and urban-dwellers can use it in the likely dry spells to come. The state’s reservoirs are for the most part filled up, and water managers have to be careful about topping them up completely, since those artificial lakes are intended both to store water for later, and to buffer cities and cropland from flooding should a big storm send torrents of water rushing toward the ocean. “California has always suffered from weather whiplash,” says Buzz Thompson, a professor of natural resources law at Stanford Law School. “We have to figure out how to manage that type of whiplash in order to get through those droughts, and avoid serious flooding during the wet periods.”
Right now, the full reservoirs have left the state with enough water to make it through one dry year (though if the wet spell ends, many residents in California’s poorer interior areas could be in trouble sooner than that, since they often rely on groundwater wells that could quickly go dry). The most recent drought, however, lasted for not one, but three grueling years. The state has been trying to store some of the excess water underground, diverting flows into fields or shallow ponds, from which water can trickle down and soak the state’s parched underground aquifers. When a dry spell returns, farmers and urban centers can tap those subterranean lakes and pull up the water stashed there.
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While the state is out of immediate water crisis for now, the overall trends are not looking good. “As a result of climate change, we're going to have more severe droughts, and more severe rainy periods,” says Thompson. “So we're likely to get more years like this year, where we have an abnormally high number of atmospheric rivers…but we're also gonna get a lot of periods like the prior three years, which was the driest three year period in the history of California.”
Jay Lund, a professor of civil and environmental engineering at the University of California Davis and vice director of the school’s center for watershed sciences, says that the water storage efforts likely won’t be enough. Even with this year’s moves to recharge California aquifers, the state is still overdrawing from its underground water supply, particularly due to agricultural irrigation, with deeper and deeper wells diminishing limited underground water. That means that despite plentiful rains this year, California is still in a long-term water crisis, which likely will require pursuing the politically and economically fraught policy of reducing water-intensive agriculture. “It's good to recharge [aquifers] as much as you can,” Lund says. “But it's not a silver bullet by any means.”
A similar story holds for the broader region—Arizona, New Mexico, Colorado, and the other arid southwest states. Both farmers and urban residents there, as well as in parts of California, are reliant on the Colorado River for water. Last year, that region was facing what looked to be a catastrophic shortfall, with a desperate political squabble between states over the diminishing water supply. Now things are looking slightly less dire, with many of the same storms that saturated California also swelling the flows of the Colorado.
Whereas California doesn’t have enough space to put its water, there’s plenty of storage in the massive Colorado River reservoirs. Lake Powell and Lake Mead, when full, can hold enough water to last the region for multiple dry years. The problem there, though, is in actually filling those reserves as states continue to draw more water than the system as a whole can handle. Lake Mead and Lake Powell were both hovering around a quarter of the way full last summer—now they’ve inched up to around a third.
“The last 20 years has been this long, almost unprecedented drought…We might need a couple more years like this year [to come out of it],” says Ben Livneh, an assistant professor of hydrology at the University of Colorado Boulder and director of the Western Water Assessment research program. “I don’t think we’re going to get a repeat.”
Most climate models show the U.S. Southwest region will continue to get progressively drier due to climate change, though there’s some chance that changes in atmospheric circulation caused by warming could bring more moisture, like what the area saw this year. Still, even if more precipitation arrives, it won’t necessarily mean more water for farmers and city-dwellers in the Southwest, since hotter temperatures will also mean more evaporation from rivers and reservoirs. “Nobody can tell you which of these two forces is going to win,” says Julien Emile-Geay, a professor of earth sciences at the University of Southern California Dornsife. “My money would be on the drying force.”
That all means that despite one wet year, there are still difficult choices ahead for California and the U.S. Southwest, which will have to decide how to allocate a shrinking pool of water among populations, industries, and political interest groups. Needless to say, it would be a terrible idea for local authorities to let up on water conservation efforts, Lund says. “It’s a little bit like saying, ‘Oh, it’s been raining this week. We should lay off the fire department.”
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Write to Alejandro de la Garza at email@example.com