John Locher / AP
What was once a marina sits high and dry because of Lake Mead receding in the Lake Mead National Recreation Area near Las Vegas, July 16, 2014.
Tuesday, April 28, 2020 | 2 a.m.
The American Southwest is in the midst of a climate-change-fueled megadrought dryer than anything the region has seen in the last five centuries, according to a new study.
Published April 17 in the journal Science, the study found that 2000 to 2018 was the driest 19-year span in the southwestern United States and northwestern Mexico since the late 1500s and the second-driest period since the year 800. Climate change and warmer average temperatures in the region appear to be worsening the megadrought.
“Almost half of the severity of this recent drought, we think the study finds, is attributable to climate change,” said Ben Livneh, co-author and assistant professor of hydrology, water resources and environmental fluid mechanics at University of Colorado, Boulder.
In contrast, the Southwest’s previous megadroughts — droughts spanning at least two decades — were probably driven primarily by La Nina conditions, said Benjamin Cook, co-author and associate research scientist at Columbia University’s Lamont-Doherty Earth Observatory. Average temperatures during today’s megadrought are also much warmer than they were during past ones, Cook said.
Warmer temperatures increase the amount of water consumed by plant life and the overall climate system, exacerbating the drought, said John Abatzoglou, co-author and associate professor of geography at the University of Idaho.
“That’s the primary mechanism here in terms of how climate change took this mediocre drought and made it into the second worst megadrought,” he said.
Led by the study’s lead author A. Park Williams of the Lamont-Doherty Earth Observatory, the researchers used hydrological modeling and tree-ring reconstruction to determine climate and moisture conditions from the year 800 to the present. The study assessed conditions in all of Nevada, California, Arizona and Utah as well as parts of Colorado, New Mexico, Idaho, Wyoming, Oregon and northwestern Mexico.
Although the Southwest benefited from a wet winter and spring in 2019, the researchers suspect that last year’s above-average precipitation could be ascribed to natural weather and climate variabilities. Over the long term, as temperatures continue to rise due to climate change, the megadrought will rage on, the study predicts.
“The Southwest is certainly a place that is prone to a lot of variability in terms of going through drought and wet cycles, and in many ways we’re sort of used to that and we develop systems that are able to deal with that,” Abatzoglou said. “What we may not be prepared for and what may really tax the system is where we begin to see these really prolonged (dry) periods.”
The epicenter of the ongoing megadrought appears to be the four corners region, Cook said. Mountainous areas are also being heavily impacted, according to Abatzoglou.
While the southern Great Basin, including the Las Vegas area, is not being hit as hard as than those areas, Lake Mead is fed by snowpack and precipitation from the Rocky Mountains.
“When it comes to water use that we depend on for food and supplies, that’s coming from the mountains,” Abatzoglou said.
Many other studies have identified a link between higher average temperatures and prolonged drought in the Southwest. But this is one of the first studies to show that “drying is already happening,” Cook said.
“Climate change is not a theoretical, future problem that we might have to deal with. It’s a problem happening right now that we really need to address,” he said.
The Southern Nevada Water Authority, which manages water supply and needs in Clark County, uses climate change projections to inform its water resource plans, said Bronson Mack, public outreach manager for the water authority.
“Studies like this continue to highlight the magnitude of uncertainty for which water agencies and water managers have to plan for,” Mack said.
The agency develops a 50-year water resource plan annually that outlines its conservation progress and priorities, existing resources and potential future resources. Officials are now developing the 2020 resource plan, which will likely be presented to the board of directors sometime in the next year, Mack said.
As the coronavirus pandemic continues to affect Las Vegas, Mack urged people staying home to follow water restrictions and avoid wasting water, especially for landscaping and outdoor use.
“It really is down to that granular level of, ‘What did I do today to save water?’” he said.
