Simultaneous extreme weather created dangerous cascades in US
Intense heat in the southwestern United States broke records last summer, in part because it coincided with an unusually severe drought, finds a new Johns Hopkins study that measures for the first time how the two extreme weather events interacted dangerously in real time.
While the drought’s impact on that heat wave was generally modest, temperatures rose by four degrees in some areas, and the researchers say similar dueling weather events likely pushed New Mexico wildfires to historic proportions this year. In addition, as climate change progresses, these one-two events and their inherent dangers will become more frequent.
“With more extremes, the possibility of extreme drought plus a heat wave and even a fire, together, there’s a greater chance it’s going to happen,” said study co-author Benjamin Zaitchik. “Understanding how a compound event can lead to a waterfall that puts you in a record-shattering situation that can really harm people and ecosystems is something many climate scientists are trying to understand.”
The findings were recently published in Geophysical Survey Letters†
Climate change is expected to increase extreme weather events, especially heat waves. There is also growing concern about more composite events, two or more weather episodes happening together, which then work together, or cascade, to become record-breaking episodes.
“We’re not just going to see records fall, we’re going to see records blown out of the water,” Zaitchik says.
The June 2021 heat wave that happened at the same time as a severe drought was an opportunity to better understand if and how real cascading events are merging to amplify conditions.
“We had the drought. We had the heat wave on top of that. Were they really cascading?” said Zaitchik, a hydroclimate scientist. “They happened together and it was bad, but what we could do with our experiments was determine if it was a cascade and if it was, did that help explain why it broke records.”
Using climate modeling and satellite imagery, the team measured the link between the heat wave and the drought. Or more simply, they found out what would happen to the heat wave if they took the drought out of the picture.
The drought pushed temperatures up by about half a degree on average, but in some areas, especially forested areas, it was four degrees higher over the course of an entire week, said lead author Mahmoud Osman, also a hydroclimate scientist and postdoctoral researcher in the United States. University Morton K. Blaustein Department of Earth and Planetary Science.
The effect of the heat on drought was more difficult to capture, both because conditions were already so deeply arid, so further drying may not have been discernible, and because the simulations weren’t designed to capture all the effects of heat on drought. Still, the team found signs, not clear confirmation, that the drought increased heat, increasing the demand for evaporation, adding to the water stress of the already very dry conditions.
Fires are another element that could easily become part of a heat/drought cascade, Osman and Zaitchik said, adding that it already seems to be happening in Texas and New Mexico this year.
“We now have earlier springs leading to earlier soil drying out, leading to increased fire risk, leading to this kind of heat/drought/fire cascade that our study is talking about,” Zaitchik said. “We’re already seeing it this year and we’re going to see it every year.”
The authors also included Nathaniel Winstead, chief scientist at the Johns Hopkins University Applied Physics Laboratory.
Intense drought could make this summer one of the hottest in Texas history
M. Osman et al, Cascading Drought-Heat Dynamics during the 2021 Southwestern United States Heat Wave, Geophysical Survey Letters (2022). DOI: 10.1029/2022GL099265
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