Science tackles the West’s megadrought
Posted on 12 April 2023 by Guest Author
This is a re-post from Yale Climate Connections by Tanya Petach and Emilio Mateo
Taps ran dry in Rio Verde on New Year’s Day.
Water had to be trucked in for household use in the affluent suburb outside Scottsdale, Arizona. The approximately 1,000 residents of the large, suburban stucco homes of Rio Verde were forced to take shorter showers and eat from paper plates.
Though the politics behind the water shut-off are complex, the crisis highlighted the impacts of climate change and the 23-year drought it has fueled in the West.
Forty million people in the southwestern United States rely on the Colorado River. Elsewhere in the vast region it serves, farmers in southern California are replacing hundreds of acres of almond trees with crops that need less water. Residents in and around Las Vegas are pulling out sod under a new law that mandates removing nonfunctional lawns by 2027, such as turf strips in commercial shopping areas or highway medians.
The Colorado River connects the Rocky Mountains to the Gulf of California, carrying snowmelt from high peaks in Colorado, Wyoming, and Utah some 1,400 miles across the arid deserts of New Mexico, Nevada, Arizona, California, and Mexico. But despite recent heavy snowfall, a severe drought has dogged the region since 2000, and the seven Colorado River states have spent months in heated negotiations as regional representatives and interest groups wrangle to wring every drop they can from the parched river system. Negotiators have missed two federal deadlines to reach an agreement on basin-wide cuts in water usage.
Meanwhile, recent studies provide an ominous assessment of the Colorado River’s future. But they also suggest a path through the stalemate with possible ways to improve water sustainability in the parched West. Along with studying focused aspects of the megadrought, they propose equally specific solutions grounded in the complexity of the system. From highlighting historic water storage agreements that yielded the greatest impact in buoying reservoir levels to new tools for drought monitoring on Indigenous lands, these studies do not shy away from the urgency and complexity of the Southwestern megadrought.
Learning from history
More than 70% of the Colorado River’s water originates as snow, so yearly flow varies with the Rocky Mountain snowpack. Throughout its history, the Colorado River has oscillated between withering droughts and catastrophic floods.
Data from paleorecord studies of the river, collected from pollen records and tree-ring widths, show extreme and persistent droughts. In 1995, a team of scientists explored the consequences of a hypothetical severe and sustained drought in the Colorado River Basin. The “SSD study,” as it became known, focused on social, economic, and environmental impacts that drought would have on the Southwest, as well as its effects on the Colorado River’s water cycle. Published at a time when the two largest reservoirs on the Colorado River, Lake Powell and Lake Mead, were both filled and annual snowpack hovered comfortably around average, the study still catalyzed water managers, policymakers, and water users to implement change and consider drought contingency plans. Lake Mead, in Arizona and Nevada, began to fill in 1935 after the construction of the Hoover Dam. Lake Powell, located some 300 miles upstream of Lake Mead in Arizona near the Utah border, was formed in 1964 by the Glen Canyon Dam.
Just five years after the publication of the SSD study, the Colorado River entered the “millennium drought,” a 23-year (and counting) period of low flows, dwindling reservoir supplies, and changing water availability across the Southwest. Though the current drought is not as severe as the one hypothesized in the SSD, flows have averaged just 60 to 75% of total allocated water rights. Lake Powell is barely above the minimum elevation for hydropower infrastructure to function properly, an elevation often referred to as power pool. Though this year’s large snowpack will help alleviate some of the pressure on Lake Powell, it will not be enough to pull the Southwest out of drought entirely. Many of the predictions in the SSD have come true, including mandatory water use cuts, vastly depleted reservoirs, and hard trade-offs between environmental and economic water uses.
From “unrealistic” drought to the new norm
In 2022, the Colorado River science community revisited the 1995 SSD’s drought predictions, implications, and effects in a new suite of studies. The SSD only referenced climate change once, but the 2022 studies incorporate global climate models. The studies project that future streamflow will likely continue to decline in the face of climate change, with reservoir levels unlikely to recover as quickly or to the full extent projected at the end of the SSD. Though the 1995 study characterized its theoretical drought scenario as “exceptionally extreme, even unrealistic,” the 2022 studies incorporate a wide range of drought scenarios, anticipating that sustained extreme drought is a real possibility and unlikely to improve as climate change worsens.
Science to action
The 2022 studies focus on actions that could alleviate the impacts of drought, building on suggestions in the SSD for increased drought resilience, economic stability, and water monitoring in the face of climate change.
For instance, one of the studies on the shaky future of recreation on Lake Mead and Lake Powell highlights the need for lakeside communities to diversify their economies beyond reservoir tourism and for basin-wide water savings to be enacted. They highlight specific management changes that have helped increase reservoir storage in past years, such as a binational agreement for water storage sharing between the U.S. and Mexico and voluntary conservation projects funded by the Bureau of Reclamation and major water groups in the Colorado River Basin. At the same time, temperature swings and the possibility of entirely dry stretches of river demonstrate the importance of significant water use reductions across the entire Colorado River Basin to increase reservoir storage.
Another study looks at the economic impacts of decreased irrigation water and potential agriculture losses on reservations in the area around Arizona and Utah, including the Navajo, Tohono O’odham, and Uintah and Ouray Nations. The study warns of reductions in cattle yields and even more severe reductions in hay yields and suggests steps on tribal lands such as increased drought monitoring, enhanced reservation access to water rights, and new tools, training, and financial assistance to recognize and respond to drought.
Another 2022 study investigates trans-boundary restoration efforts in the Colorado River Delta between the U.S. and Mexico. Habitat restoration has been successful and a common goal for both countries, yet restored areas are small and will continue to rely on support and water delivery. The study suggests alternative water sources to continue conservation efforts in the face of severe drought.
These studies are a prime example of scientists bridging the research-practice boundary. In a changing climate, these bridges are more important than ever to identify practical solutions that can protect people and wildlife. The 2022-2023 snow year looks promising so far. But after more than 20 years of drought, one good year’s snowpack won’t replenish the basin. Still, this year may provide a short window for the Colorado River Basin to catch its breath and for the scientific community to add its recommendations to the ongoing water negotiations in the Southwest. Given what is likely coming, we have no more time to delay.
Tanya Petach and Emilio Mateo are Climate Science Fellows at the Aspen Global Change Institute, which is a Yale Climate Connections content-sharing partner.