Megadroughts will continue because it’s only getting warmer

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Even after potent summer rains deluged parts of the West, nearly 60 percent of the region remains mired in extreme or exceptional drought.

The biggest reservoirs in the U.S. — Lake Mead and Lake Powell — have already fallen to historic lows. Dead cattle decay on the ground in parched Northern Mexico. California’s reservoirs look like bathtubs continually losing water.

This isn’t typical drought. The warming Southwest is in an over two-decade, prolonged drying period — the worst megadrought in at least some 400 years — in addition to a two-year dearth of rain and snow in California, and abnormal dryness in other regions.

When or how droughts might end in different Western places is a looming question. But in the continually heating West, it’s not the most crucial question.

“The real challenge is when the recent drought does end, what are we going to do to prepare for the next one?” emphasized Benjamin Cook, a research scientist at Columbia University’s Lamont-Doherty Earth Observatory who studies drought.

It’s a salient question because large swathes of the West are getting drier. The trends in dropping reservoir levels and shrinking snowpack paint a clear, stark picture. “All of this points to us moving into a drier average future,” said Cook.

Sure, it’ll rain hard again. “You get one good year and things ostensibly look fine and people forget there was ever a drought.” But more troubling, even hotter droughts will come. What follows is insight into the current Western droughts, and how we might adapt.

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Understanding the droughts

There’s not a single drought happening. Think of it as three significant regional droughts happening at once:

1. The Southwestern megadrought: This “hot drought,” driven by warmer temperatures, heavily impacts the seven states and Mexico that rely on water in the Colorado River basin. The drought is so bad, the governor of Utah has asked Utahns to pray for rain.

2. California drought: The Golden State relies on winter rains and snowpack stored in the lofty Sierra Nevada to refill its reservoirs. Much of the state has received less than half its normal rainfall since last fall. In large swathes of California, it’s the second-driest two-year period on record.

3. Pacific Northwest drought: “Most of the Pacific Northwest is experiencing abnormally dry or drought conditions,” the U.S. Drought Monitor said in late July. The dryness has helped fuel massive fires in Oregon.

The Colorado River basin.
Credit: usgs

The bathtub ring around Lake Mead reveals dropping water levels.
Credit: MICHAEL VI / shutterstock 

The droughts won’t all end at once. “[There’s] no doubt that the West is in a pretty deep hole when it comes to the current level of drought,” said Jonathan Overpeck, a climate researcher at the University of Michigan. “As to what it’ll take to get out of this hole, that depends on what part of the West you’re focused on.”

Drought experts largely agree that a wet season with strong, above-average precipitation will be enough to moisten the parched grounds in California and the Pacific Northwest, and to refill California’s dropping reservoirs. “There is hope that drought can turn around fairly quickly if the fall and winter coming up is a good one, a wet one with good snowpack in the mountains,” said Dan McEvoy, a regional climatologist at the Desert Research Institute and the Western Regional Climate Center, both environmental research organizations.

Yet the past couple of decades proved that even if a wet year (like 2019) tempers a drought, drought can easily return (like 2020 and 2021). “Droughts can be erased pretty quickly by a single wet year, but are not gone for good,” explained Michael Dettinger, a hydroclimatologist and currently a research professor at the Desert Research Institute. “A single subsequent dry year will see drought reemerge to an extent, and multiple dry years will make for the worst droughts as effects pile up. A normal precipitation year does not somehow heal a drought, but it sure helps.”

Crucially, in the “boom and bust” water cycle in California, the wets are getting wetter but the drys are getting drier, a trend researchers expect to continue in the future. “We do expect more extremes, more wet and dry,” noted McEvoy.

“As long as climate change continues — as long as the burning of fossil fuels continue — it will get harder and harder to get out of the drought/megadrought.”

But the prolonged Southwestern drought can’t be so quickly remedied, at least temporarily, in just a year or so. Refilling the massive Lake Mead and Lake Powell reservoirs, which are fed by the long, snaking Colorado River, will require repeated, strong doses of rain and snow. (Already, for the first time in Lake Mead’s 85-year existence, water levels may drop below a point this summer that triggers water cuts in Arizona and Nevada.) “It will take ever-increasingly large and anomalous multi-year periods of cool-season wet conditions to offset current drought conditions,” explained the University of Michigan’s Overpeck.

In a hotter Southwest, it’s easier to fall into drought and more difficult to climb out. Under a warmer climate, more water evaporates from rivers and reservoirs, more snow sublimates (goes from a solid to gas) from mountains, and trees and plants lose significantly more water to the drying, warmer air.

“As long as climate change continues — as long as the burning of fossil fuels continue — it will get harder and harder to get out of the drought/megadrought,” said Overpeck.

We’re not helpless

The good news is, even in the face of declining water availability, society can use less water, and use it more efficiently. We can prepare.

“We do have agency to control our water use,” said Cook.

It’s necessary. Arizona’s population, for example, is expected to double in the next half century. The dropping water levels in Lake Mead and Lake Powell are a consequence of more water being used than the system now supplies, explained Cook. Many Western and Southwestern rivers are already over-allocated, added Overpeck.

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So how do we adapt? Southwestern states already have agreed to the Colorado River Drought Contingency Plan, which results in (among other plans) automatic water cuts to avoid critically low reservoir levels. Here are two important areas to slash water use:

• Agriculture uses some 80 percent of water from the Colorado River. This means minimizing water loss when irrigating crops. It could also mean switching crops or retiring 10 percent of water-hungry farmland (like alfalfa), which would conserve bounties of water, according to Bruce Babbitt, a former Secretary of the Interior and Governor of Arizona.

• Majorly cutting water use in urban areas. For example, in the Las Vegas region, the “community used 23 billion gallons less water in 2020 than in 2002, despite a population increase of more than 780,000 residents during that time,” according to the Las Vegas Water District. This means a focus on limiting outdoor water waste, which lets water evaporate. Since 1999, some 197 million acres of grass were replaced by desert landscaping in the Vegas area. What’s more, the Nevada legislature recently passed a law prohibiting Colorado River water from irrigating decorative grasses (in medians, etc.). “This decorative grass consumes about 10 percent of our annual water supply — more water than is consumed by the entire Las Vegas Strip,” the water district said.

• Slash carbon emissions: All the future droughts, whether in California, Oregon, or the Southwest will be less severe if Earth’s warming is stabilized at around (a still markedly warmer) 3.6 degrees Fahrenheit (2 degrees Celsius) above 19th-century levels. This is the current, though ambitious, international climate goal, and requires a rapid movement away from a fossil fuel-dominated energy system. Warmer temperatures evaporate more moisture from vegetation, water bodies, and soil, making bad drought worse.

A drier climate regime has arrived, and will continue to dry. It will still rain, sometimes in deluges, but the trends are clear: The frequency of reliable periods with strong, wet precipitation isn’t as likely anymore.

“The odds just continue to go down as long as we keep burning fossil fuels and driving climate change,” said Overpeck.

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