Cascading Drought-Heat Dynamics During the 2021 Southwest United States Heatwave

In June of 2021 the Southwest United States experienced a record-breaking heatwave. This heatwave came at a time when the region was in severe drought. As drought alters the surface energy budget in ways that affect lower atmosphere temperature and circulations, it is possible that the combined drought-heat event was a cascading climate hazard, in which preexisting drought exacerbated the heatwave. We apply satellite observation and numerical experiments with the Weather Research and Forecasting (WRF) model to test for land-atmosphere feedbacks during the heatwave consistent with drought influence. We find a modest positive drought-heat effect, as WRF simulations that include the drought have marginally higher air temperatures than those that exclude the initial drought conditions, with more substantial effects in wetter, forested areas. Evidence of drought-heat-drought-coupled feedbacks was similarly modest in our simulations, as accounting for drought preconditioning led to a small reduction in simulated precipitation in the region.

Automated summary

In June 2021, the Southwest United States experienced a record-breaking heatwave and severe drought. The study found that drought conditions may have exacerbated the impact of the heatwave, especially in wetter, forested areas.