When Will the Megadrought Gripping Southwestern States End?

California and other southwestern states have been in the grip of a megadrought for the past two decades.

Scientists say that, despite recent storms, these drought-stricken states won't be relieved from the hot and dry weather for a long time, and not without large amounts of rain.

"To break the megadrought, the region will need to see consistent levels of rainfall at or above average levels for several years," Hannah Cloke, a professor of hydrology at the University of Reading in the U.K., told Newsweek.

The term "megadrought" is generally defined as an extended period where rainfall levels remain below average for many years.

"Megadroughts typically refer to droughts that are very severe and also span many years (decades). They also typically have a large geographic spread," Antonia Hadjimichael, an assistant professor in geosciences at Penn State University, told Newsweek.

The severe drought in the Southwest of North America is considered to be the longest and driest extended period of drought the region has seen in more than 1,000 years. The current megadrought has been going on since around the year 2000, and has led to severe drying of many important reservoirs and rivers across the region, including Lake Mead and the Colorado River.

"The drought started around the turn of the century and has carried on pretty much unabated since then, with only limited rainfall providing some relief in some parts," Cloke said.

"This region of the Americas has experienced long periods of drought before, with perhaps two or three megadroughts each century over the past 2,000 years. But this megadrought stands out from the record as being particularly long lasting."

The long-lasting drought has led to severe water shortages in areas of the Southwest, with major decreases in the water levels of key reservoirs, including Lake Mead and Lake Powell, two reservoirs on the Colorado River. Both reservoirs are critically important for providing water to millions of people across Arizona, California, Nevada, New Mexico and Utah.

"This megadrought, or prolonged period of dryness, has lasted some two decades now in the Southwest leading to a real decline in our two major reservoirs in the basin—Lake Mead and Lake Powell," Andrea K. Gerlak, a geography professor at the University of Arizona, told Newsweek. "Both reservoirs are experiencing record-setting lows leading to concerns that there won't be enough water for all of the cities, farmers, tribes, and businesses that have been promised water and have built an economy around Colorado River water."

While the recent rains have refilled the reservoirs across many of the states significantly, including Lake Oroville and Lake Shasta in California, the drought won't be entirely lifted until the groundwater stores are replenished. This is a task that will require large amounts of rainfall combined with water management to achieve.

"It will take several years of above normal precipitation—both rain and snow during the appropriate times of year," Lara Fowler, an environmental and energy issues attorney and interim director of the Penn State Sustainability Institute at Penn State University, told Newsweek. "As soil moisture and surface water supplies have become depleted, more and more groundwater pumping has also led to a decline in aquifer levels in many places. Such groundwater contributes to baseflows in streams. So not only would surface water (streams/rivers) need to refill, so does soil moisture and groundwater levels (the last of which can be very slow to recharge)."

"Even with the record snowpack in much of this region since January, there is still an on-going drought given the underlying conditions (low groundwater, previously poor soil moisture, and badly depleted reservoirs). It's like we've spent down our bank accounts and it will take quite a while to rebuild—one year of good snowpack helps a lot, but is definitely not enough," Fowler said.

If the drought continues for much longer, water shortages may become an increasingly large issue across the country.

"The impacts of severe drought can have enormous consequences on agricultural ecosystems and water supplies, including declining productivity and reduced groundwater and reservoir supplies that supply fresh water to cities and towns," Erica Smithwick, a professor of geography at Penn State, told Newsweek.

Additionally, the drought will increase the risk of forest fires, reduce power generation capacity from hydroelectric dams, and lead to the deaths of many species of animals and plants.

Climate change is expected to exacerbate these issues, as it will increase temperatures and change rainfall patterns across the Southwest.

"Experts estimate that a large part of this loss in flow we're seeing can be attributed to higher temperatures in the region, a result of human-caused climate change. This was not the case with previous comparable droughts (like in the 1950s), which were primarily caused by lack of precipitation. With climate change, temperatures are likely to continue to increase, exacerbating the risks for such prolonged droughts," Hadjimichael said.

A study published in the journal Nature Climate Change in 2022 showed that 42 percent of the dry and hot conditions across the U.S. over the last two decades can be attributed to climate change.

"We know that climate change as a result of human activity is already making droughts worse. This is because of shifting weather patterns, influenced by the changes in temperatures in oceans and the atmosphere, in part because warmer air holds more moisture. This is one of the reasons why extreme weather is getting more extreme—heavy rainfall can be even heavier, and droughts can last longer," Cloke said.

Last year, the U.S. Department of the Interior asked states on the Colorado River basin to develop plans to make cuts in their water use in order to maintain water flow in the river.

"The ask is extraordinary—states are tasked with voluntarily deciding how to cut nearly one-third of current water use," Gerlak said. "Imagine cutting water use in your home by one-third. What would you give up? How would you make the cuts? Now consider that on the larger scale of 40 million people across 7 western states and two countries. Despite all the conservation measures adopted across the basin in the past two decades, demand now far outreaches availability in the river due to climate change. There is no way around it, we are in crisis."

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