After the drought, the deluge. For the past two weeks, in the United States, California has been hit by a series of atmospheric rivers, long corridors of humidity carrying water vapor from the tropics that can cause very heavy precipitation on landfall. Torrential rains and floods have already caused the death of 18 people, a toll which could increase, the return to calm not being expected before January 18.
However, these downpours do not solve another problem that has lasted four years in California: the drought. “Even though the rains that have fallen in recent weeks have been exceptional, in Northern California we have barely reached half the usual level of annual precipitation,” notes Helen Dahlke, professor of integrated hydrological sciences at the University of California, Davis.
“We are clearly not out of the woods yet,” adds Jenny Pensky, hydrogeologist at the University of California at Santa Cruz. We could very well relive the same scenario as last year, namely heavy rainfall around New Year’s and then nothing in February and spring. In June, the state had to put in place drastic water restrictions.
While the Golden State is currently seeing the bed of its rivers swell, some Californians denounce the lack of infrastructure that would store this precious resource. In Los Angeles, as in other cities, “a system of artificial waterways was built to discharge stormwater into the ocean, a strategy that was intended to reduce the risk of flooding” but which “waste” now “countless liters of water”, recently regretted the journalist of the Los Angeles Times, Hayley Smith.
California has reservoirs, but built several decades ago, at a time when the climatic data was different. “One of the disadvantages of reservoirs as a storage tool is that at some point they have to be emptied to make room for new water arrivals,” explains Jenny Pensky.
Farmland to store rainwater
“Rather than having recourse to surface reserves initially designed to protect the population from the risks of flooding, we must instead focus on recharging our underground reserves”, believes Helen Dahlke. Infiltration basins do exist in California, but their number is “not sufficient”.
With her research team, Helen Dahlke believes that agricultural land could be used massively to store rainwater and thus recharge groundwater. In the agricultural central valley, this type of project has already begun to see the light of day. “Flood water is channeled to land where vines or almond trees are grown, and the crops are flooded to allow the water to penetrate underground,” explains the hydrologist.
In the Pajaro Valley, south of San Francisco, the water management agency has even set up a pilot subsidy program to encourage farmers to turn their land into underground storage ponds.
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