Severe Drought, Worsened by Climate Change, Ravages the American West

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ALBUQUERQUE — This year, New Mexican officials have a message for farmers who depend on irrigation water from the Rio Grande and other rivers: Unless you absolutely have to plant this year, don’t.

Years of warming temperatures, a failed rainy season last summer and low snowpack this winter have combined to reduce the state’s rivers to a relative trickle. The agency that controls irrigation flows on the Rio Grande forced the issue. To conserve water, it opened its gates a month later than usual.

Severe drought — largely connected to climate change — is ravaging not only New Mexico but the entire Western half of the United States, from the Pacific Coast, across the Great Basin and desert Southwest, and up through the Rockies to the Northern Plains.

In California, wells are drying up, forcing some homeowners to drill new ones that are deeper and costlier. Lake Mead, on the border of Arizona and Nevada, is so drained of Colorado River water that the two states are facing the eventual possibility of cuts in their supply. And 1,200 miles away in North Dakota, ranchers are hauling water for livestock and giving them supplemental forage, because the heat and dryness is stunting spring growth on the rangelands.

The most dramatic, and potentially deadly, effect of a drought that is as severe and widespread as any seen in the West are the wildfires that are raging amid hot and dry conditions. And this is well before the full blast of summer’s heat arrives.

California, Arizona and New Mexico have each had two large blazes, unusual for this early in the year. None has been fully contained, including the Palisades Fire, which has burned 1,200 acres on the outskirts of Los Angeles.

Officials are predicting when the fire season ends — if it ever does, as warming conditions have made fires possible year-round in some areas — the total could exceed last year’s of 10.3 million acres.

“The signals and indications are that we are heading for another very dangerous fire year,” Secretary of Agriculture Tom Vilsack, whose department includes the Forest Service, said last week after he and Interior Secretary Deb Haaland were briefed by experts from the National Interagency Fire Center. “We’re seeing a higher level of risk and an earlier level of risk than we’ve seen in the past.”

“There’s two things going on,” Dr. Musselman said. “First, there’s less precipitation. But on top of that there’s this backdrop of warming. That’s altering the delivery of that water.”

More meltwater runs off the mountains sooner, wreaking havoc with the ability to store proper amounts in reservoirs for use during the dry summer. Too much runoff too soon also eventually causes stream flows to drop rapidly.

And low stream flows can lead to a number of other problems, given that shallower water warms more rapidly. In California, for instance, some salmon hatcheries are trucking young fish directly to the ocean this spring, fearing that they wouldn’t survive swimming in the warmer water of rivers that have been affected by drought.

Heat and dryness have a particularly strong effect on the conditions that lead to wildfires, decreasing moisture in the soil and drying vegetation so that it ignites more readily and burns hotter. That can make fires spread more easily.

Severe drought can also result in mass die-offs of trees, providing enormous quantities of fuel for any potential fire. The Forest Service reported one such die-off in April in Arizona, where up to 30 percent of the juniper trees across about 100,000 acres had died from the drought.

Dry conditions can also make warming worse, said Amir AghaKouchak, who studies climate-related and other water resource issues at the University of California, Irvine. Warming causes soil to lose moisture through evaporation, which has a cooling effect on the surface of the ground, much as evaporation of sweat from skin causes a person to cool down. But eventually so much soil moisture is lost that the process stops.

“During droughts, moisture levels become very low, so evaporation doesn’t happen,” Dr. AghaKouchak said. “The skin of the earth warms up, and that warms the atmosphere.”

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