The U.S. is set for an El Niño winter—the warmer counterpart to La Niña—a climate pattern that starts with warm water building up in the tropical Pacific Ocean west of South America.
During El Niño, the U.S. usually experiences drier than usual conditions in the North, and wetter conditions in the South, including famously dry areas across the Southwest that have suffered prolonged drought conditions.
Due to the drought, integral reservoirs such as Lake Mead, which is on the border of Nevada and Arizona, have suffered from catastrophically low water levels. In July 2022, the reservoir reached its lowest point of 1,040 feet after a particularly dry year.
So will an unusually wet winter period caused by El Niño mean good things for the reservoir? The short answer is yes, hopefully. But weather patterns can be hard to predict.
"We [need to] wait to see what this winter's snowpack will look like," Andrea K. Gerlak, director of the Udall Center for Studies in Public Policy and a professor at the school, told Newsweek. "Since it is an El Niño year, we might see a wet year for the Rockies, which is good news for Colorado River flows and levels at Lake Mead."
Lake Mead is on the Colorado River, which is fed by seasonal snowpack running down from the mountains.
In recent years, dry conditions and an overconsumption of water have meant that the available snowpack has not done much to replenish the lake. Scientists believe climate change has made weather patterns more unpredictable, meaning there is less annual snowpack than there once was.
During particularly wet winters, more snowpack accumulates in the mountains, meaning more water for Lake Mead.
A wet, El Niño winter could mean higher than average snowpack levels.
"For the U.S., the higher eastern Pacific Ocean temperatures help to increase rainfall in the South, but for the Midwest and Northeast it's typically drier," Andrew King, senior lecturer in climate science at the University of Reading, told Newsweek. "As El Niño events last several months, these shifts in weather systems can result in normally dry places experiencing more floods and normally wet places experiencing drought."
Last winter was set in La Niña—which is usually characterized by prolonged periods of dry weather and drought in the Southwest. But the region was battered by storms, which built up higher than average levels of snowpack, causing Lake Mead's water levels to rise significantly when it began to melt in May.
"El Niño events are characterized by shifts in Pacific Ocean conditions in both the ocean and atmosphere," King said. "Normally the eastern tropical Pacific is quite cold and the western tropical Pacific is warmer, but during El Niño, this temperature difference across the Pacific Ocean decreases as the east Pacific warms up.
"There is an associated shift in weather patterns as low pressure tends to form over warmer ocean surfaces. As the typical weather patterns move around over the Pacific, this also affects where weather systems move in other parts of the world, but particular in areas near the Pacific."
Lake Mead's water levels stand at 1,066.24 feet as of Monday. The lake rose steadily due to the higher than average snowpack throughout the spring and summer, and has now slowed. In recent weeks, the lake has declined slightly along with the change in weather patterns.
"The decline in water levels at Lake Mead is expected," Gerlak said. "In this highly engineered system that we have in the Colorado River basin, this period of depletion is both scheduled and expected."
Gerlak warns, however, that even if the lake is replenished slightly by seasonal rainfall, there is still a wider issue.
"It is easy for us to come to see the health of the river through the levels in our reservoirs—most notably, Lake Mead," Gerlak said. "But the conditions at Lake Mead are really just one signal of the health of our larger river system.
"Although not at all as visible, groundwater is also a signal of the health and vitality of the Colorado River system. And unfortunately, the overall condition of our groundwater resources across the basin are poor and declining."
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About the writer
Robyn White is a Newsweek Nature Reporter based in London, UK. Her focus is reporting on wildlife, science and the ... Read more
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