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Emerging, decades-long megadrought emerging for the Southwest

Emerging, decades-long megadrought emerging for the Southwest

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PHOENIX – It’s the early 1990s, and Park Williams stands in the middle of Folsom Lake, at the base of the Sierra Nevada foothills in Northern California. He’s not walking on water; severe drought has exposed the lakebed.

“I remember being very impressed by the incredible variability of water in the West and how it’s very rare that we actually have just enough water,” said Williams, who went on to become a climate scientist at Columbia University. “It’s often the case there’s either too much or too little.”

Williams is the lead author on a report out this month in the journal Science detailing the extent of drought conditions in the American West.

The report found the period from 2000 through 2018 to be the driest 19-year span since the late 1500s, and the second-driest since 800. In simpler terms, it’s an emerging megadrought, which is a drought that typically lasts decades.

“Drought conditions during the 2000s have actually been on average as severe as the driest on 20-year periods of the worst megadroughts of the last millennium,” Williams said in an interview with Cronkite News. “The cause is a combination of natural climate variability and human-caused climate change.”

What sets this emerging megadrought apart from others, such as those recorded in the 1200s and 1500s, is that human activity is increasing the severity. Although past megadroughts had natural causes, the report found this natural phenomenon has been made worse by humans.

Nancy Selover, Arizona’s state climatologist since 2007, said there’s more to learn about the impact people have had on this recent drought, although she does classify Arizona as being in a megadrought now.

“I’m sure we’re contributing a little bit. I’m not sure how much we’re contributing,” Selover said. “It’s model output. And models are designed not to predict what’s going to happen; they’re designed for us to understand them and learn how the system works.”

It’s important to understand the difference between deserts and droughts, said Kathy Jacobs, the director of the Center for Climate Adaptation Science and Solutions at the University of Arizona.

“I think making a distinction between sort of living in a desert where it’s hot and dry, and understanding that we could be entering into decadeslong shortage situations that really throw all of our water supply projections for a loop is a really important distinction,” Jacobs said.

To make that distinction, Williams and his team employed methods first used by researchers at the University of Arizona in 1937, who discovered the width of the annual growth rings in tree trunks corresponded to moisture availabilities, or soil moisture.

“Our measurement of drought is really a combination of tree ring records that come up to 1900,” Williams said. “And then that, stitched together with our climate derived estimates of soil moisture, brings us up to 2018.”

He said a megadrought isn’t a multidecade period in which every year is dry, but instead an extended period when the occasional wet years don’t come close to making up for the predominance of dry years.

If the concept of an emerging megadrought seems abstract, there’s a reason. Williams said people might not immediately feel the impact of water sources depleting due to groundwater pumping in California, Arizona and other states.

“We’ve been pulling out groundwater at a far faster rate than it actually gets replenished, and that has allowed us to get through this drought,” Williams said. “We’re basically borrowing from the future.”

Selover said it’s a future that’s likely to include more people in the Southwest.

“We now have more people here, so drought is a more significant issue than it ever was before,” she said. “We need to be very, very careful about how we deal with our water and how we deal with our temperature. Because those things going forward are going to be decreasing water and increasing temperature.”

The Colorado River is one example of decreasing water resources. Arizona, California, Colorado, Nevada, Utah, Wyoming and New Mexico depend on the river for water, but the amount of water each state is promised has been consistently overallocated.

“Each state is actually guaranteed more acre feet of water out of the Colorado River every year than actually flows in the Colorado River in an average year,” Williams said. “We’ve had an unsustainable relationship with the Colorado River for the last century, independent of climate change.”

Jacobs said it’s a relationship that hasn’t been properly addressed, especially considering the cultural significance the Colorado has to many people in the Southwest.

“It’s really important to recognize both tribal and environmental uses of water in both the main stem (of the river) and the tributaries,” Jacobs said. “Letting the river actually be a river and flow is something that’s valued by some people. Whereas now, we have essentially dried the entire river out so it does not reach the sea.”

Williams suggests that water in the 1,450-mile-long Colorado be reallocated as one way to improve the river’s condition. That’s difficult when the demands for water are so high.

Last year, after years of negotiations, President Trump approved the Colorado River Drought Contingency Plan that outlines how much water the seven Colorado River Basin states can take from the river if reservoirs at Lake Powell and Lake Mead drop to critical levels. Despite the plan, Williams said the river still is in danger of drying up.

“The fact that the normal average year is actually getting drier and is projected to keep getting drier in the Colorado River means that we’re probably going to have to revise how much each state is allocated on the Colorado River substantially,” Williams said.

Beyond that, Jacobs stresses the need to elect representatives to the Arizona Legislature who care about the environment and to reach out to current legislators so they know how important tighter water regulations are to Arizonans and the state’s economy.

“Most of the people who come here for tourism are coming because they want to see the beautiful parts of the state,” Jacobs said. “Many of those beautiful parts are connected to rivers and water supplies. There are billions of dollars generated by the state’s economy by people who are here for ecotourism, and we could easily build that into a much more profitable path.”

At the end of the day, the spirit of continued water conservation efforts can be traced back to that image of a young Park Williams on Folsom Lake. The lesson learned, he said, is how precious water is.

“The stakes for humans are higher than they’ve ever been before,” Williams said. “And as we change the climate, one of the things that is most predictable is that the distribution of water is going to change. Trying to figure that out before it really becomes a crisis, I think, is one of the most valuable things we can do.”


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