When the rain finally came to Dallas this summer, it came with a vengeance. With more than a week left in August and on the heels of a historic dry period, the Dallas-Fort Worth area set its record for the wettest month, with more than 10.38 inches of rain breaking a century-old mark. More than nine inches of that fell in a single 24-hour period.
This biblical deluge, which flooded homes, sent emergency crews scrambling to respond to hundreds of calls, and killed at least one person when her car was swept off the road, hit the Dallas area immediately on the heels of an extended drought. The January to July period of this year was the seventh-driest recorded over the last 128 years in Dallas County, leaving thirsty lawns and gardens and cracked, parched ground, setting the stage for the damaging rains to come.
In what may seem like a paradox, these very different weather extremes are being juiced by the changing climate, even in the exact same location. Hotter and drier, and then very suddenly much wetter — a climate change double-whammy that will arrive more and more often, bringing potential calamity with it.
These changes, driven by the accumulation of greenhouse gases in the atmosphere, are magnified by basic geology. Although areas that have suffered through extended dry periods desperately need water in most cases, prolonged hot, dry conditions can kill plants and harden topsoil, sometimes making the ground less able to accept water when it comes.
Nicholas Pinter, a professor and associated director of the University of California, Davis, Center for Watershed Sciences, said these opposing extremes are entirely consistent with the predictions of climate science. “The expectation is that the droughts are going to be worse and more frequent, and then potentially the floods the same,” he said.
This is true across many regions, and Texas-specific research bears it out as well. A report on extreme weather led by Texas state climatologist John Nielsen-Gammon projects that by the state’s 200th birthday in 2036, droughts will become more severe compared to the 2000 to 2018 reference period. At the same time, extreme precipitation events will become 30 to 50 percent more likely than they were in the latter half of the 20th century.
“One of the oldest predictions of climate science is that the variability of rainfall is going to increase,” said Andrew Dessler, a professor and director of the Texas Center for Climate Studies at Texas A&M University. “Increasing variability means that you’ll have more dry periods, which increases the chance of intense drought. When it does rain, it’s going to rain harder” thanks to the warmer atmosphere’s ability to hold more moisture, he said. “That’s going to increase the chance of events of floods like Hurricane Harvey or the event in Dallas.”
That’s true in many places around the globe.
Like Texas, China has also boomeranged from extreme floods to equally intense droughts. Last summer, Zhengzhou, the capital of central China’s Henan province, became a symbol of the damage the country’s floods can wreak. Zhengzhou’s broad boulevards turned into roaring rivers and 14 people died after water surged into the subway system — it was like a scene out of a horror film that was captured in videos by those stuck in the submerged cars as the water rose above their chests.
Extreme floods like the one that hit Zhengzhou are becoming increasingly frequent and severe in China. Researchers have found that the country will be among the most vulnerable to flooding as temperatures climb. And these disasters take an economic toll — one 2019 study concluded that factory output fell by nearly one-third in the Yangtze River region after large floods.
But this summer, the area around Zhengzhou is facing the opposite problem. Drought has descended on millions of hectares of farmland after a record-breaking heat wave that has hit a historically wide swath of China. Most of the country is projected to see more frequent and intense droughts in the coming decades. And they too have a huge economic bite. In Sichuan, the current drought has cut into the province’s main source of electricity, hydropower, forcing all factories — including production of critical solar panel ingredients and electronics at Apple supplier Foxconn’s facilities — to shut down for a week to save electricity.
The varying dry and wet extremes climate change is creating can also increase the risk of another deadly disaster: landslides.
In California, where drought is also a persistent and increasing concern, the drying landscape is ripe for wildfire. And in the wake of those fires, when the ever-more-powerful rainstorms hit, they destabilize hillsides that now lack the vegetation that held them together. Catastrophe can follow.
“When you’ve got this intense rainfall on top of a burned area, that’s really the blinking red warning light,” Pinter said.
The warning proved deadly in 2018, when torrential rains in Montecito, near Santa Barbara, sent mud and boulders screaming down the wildfire-torn Santa Ynez mountainsides. When it was over, 23 people had died.
This will be a global problem as the climate changes, though sometimes the mechanism will take forms other than wildfire. For example, a 2020 study found that landslide risk in the Himalayas will increase by the end of the century, potentially exacerbating the “cascading hazards” for people living downstream of melting glaciers and glacial lakes. The researchers noted that landslide risk will likely increase everywhere from northwest Canada to the Andes and eastern Africa.
In Dallas, the period of drought preceding the flood likely prevented even worse outcomes, Pinter said, because saturated ground would provide even less place for all the incoming water to go. But there are other hazards associated with that drought-flood one-two punch.
“Flooding in particular is this long-term persistent threat,” Pinter said. “It doesn’t go away just because you’ve had four or five years of drought.” Flood protection and related systems can degrade over time, so even in extended periods of dry, hot weather there is reason to keep preparing for climate change’s other contributions. “You cannot let your guard down.”
Thanks to Alicia Benjamin for copy editing this article.