Torrential rains in California since the start of the year have filled the state’s water reservoirs. But reserve management remains fragile throughout the American Southwest, where the low level of the Colorado River has remained virtually unchanged.

The 12 atmospheric rivers that have hit the California coast since the start of 2023 have filled several large water reservoirs in the northern and central parts of the state. A glance at the California water resources map shows that current levels at Oroville, Shasta, New Bullards, Don Pedro, Camanche and other reservoirs are above their historical average1.

Faced with this resurgence, Democratic Governor Gavin Newsom announced, on March 24, relaxations in water consumption restrictions.

But we must remain very cautious in the face of this good news. Because they come with some bad sides, explains Amir Aghakouchak, associate professor at the Center for Hydrometeorology and Remote Sensing at the University of California at Irvine.

According to Mr. Aghakouchak, this very contrasting phenomenon could repeat itself in closer sequences in the future. “In 2017, we experienced the same situation: a five-year drought suddenly interrupted by major floods. We have to be prepared for more sudden changes. We cannot assume that we will experience long lulls. »

In the Salinas Valley, an area halfway between San Jose and Monterrey, the rain did cause significant flooding. The damage to agricultural land is considerable. The price of lettuce, grown in abundance in this region, should increase shortly and remain high for months.

Strawberry fields were also affected.

“From north to south, wildlife, farmers and farm workers have not been spared,” confirms Chris Lopez, Monterey County Supervisor where the Salinas Valley is located. People’s jobs are affected. »

Another issue that should not be overlooked is the impact of recent rains on California’s groundwater levels. According to Alexis Maximilien Berg, assistant professor in the geography department at the University of Montreal, a winter of heavy rains will not be able to raise them.

Recent rains have failed to raise the level of the Colorado River, which remains desperately low, as La Presse reported on February 1, 20232. The levels of the two largest reservoirs of this river, Lakes Mead, in Nevada east of Las Vegas, and Powell, on the Utah-Arizona border, have risen a bit in recent weeks. But they remain far from the average.

Created on the Colorado River by the construction of the Hoover Dam, the artificial Lake Mead constitutes, when filled, the largest reservoir of drinking water in the United States. It serves some 20 million people in Arizona, Nevada and California. At maximum capacity, its water level is 375 meters above sea level.

“Sometimes the atmospheric rivers, after pouring most of their water over California, also leave some in the Colorado basins. But not this time. The drought continues,” observes Amir Aghakouchak.

“If nothing is done, lakes Mead and Powell could become what are called “dead pools”, indicates Alexis Maximilien Berg. Initially, the power plants of the dams will no longer be able to produce electricity. In a second step, the water will no longer come out of these. »

The river’s water level is so low that the seven states that partly depend on it have been ordered by the federal government to come up with a plan to reduce their consumption – it was to be presented by January 31 at the latest. However, there was no agreement because California, the largest consumer, refuses to join the agreement signed by the six other states. The project is still on hold.