LAS VEGAS (KLAS) — What was once an open desert is now an urban metropolis with miles of above and below-ground water diversion channels and tunnels to keep human-inhabited parts of the Las Vegas valley dry. But the Las Vegas valley didn’t always need man-made tunnels to divert water — over the course of millennia the desert created its own flood channels, many of them built over with homes, roads, and parking lots.

This change in the urbanization of the valley is the focus of a new study published on Jan. 6 in The Journal of Hydrometeorology, from the Desert Research Institute (DRI), the Clark County Regional Flood Control District, the University of Wisconsin- Madison, and Guangdong University of Technology. The study shows that flood intensity in the valley took an “abrupt shift” in the mid-1990s.

Las Vegas valley – 1984 (left) compared to 2020 (right) – (Source: Google Maps)

It also looked at how climate change shifted the timing of seasonal flooding. It showed floods now happen more in winter instead of the historically more active summer monsoon season.

“When I looked at the data for annual flood peaks, I could see that something is changing,” said Guo Yu, Ph.D., lead author on the new study and hydrologist at DRI. “I wanted to understand the reason for this change as well as the physical mechanisms driving it, because that will help water managers and the public understand whether such a change will continue in the future, given climate and land use changes here.”

Highlighted in the story is the rapid population growth in the valley. In 1950 there were around 35,000 people living here. But by 2020 the population had climbed to more than two and a half million.

“Historically, people in Las Vegas haven’t paid as much attention to winter floods as to summer floods,” Yu said. “But our research shows that there will be more frequent winter floods happening because of climate change. This is because the warmer sea surface temperatures on the Pacific coast will cause more atmospheric rivers, like what we’re seeing this January in California. And when these are positioned to bypass the Sierra Nevada mountains, they will very likely hit Las Vegas and cause severe winter rainfall and floods.” 

“A lot of research focuses on a single driver – either land use or climate – but in Las Vegas, our study shows that both are changing and interacting with each other,” said Yu.