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. Plain Language Summary: In June 2021 the Southwest United States was hit by a record‐breaking heatwave at the same time as a severe drought. In this study, we look into the response of both events effect on one another. The WRF computer model is designed to test the observed events besides the use of satellite images during the same time. We find a small positive response between the two events that was more considerable over wetter and green regions. We also find a decrease in rainfall over the study region as a response to the drought‐heatwave conditions. Key Points: The record‐setting 2021 US heatwave struck at a time when surface conditions were anomalously dry, bright, and barren due to droughtSatellite observations indicate that drought led to anomalous land‐atmosphere fluxesModel simulations also indicate a small but systematic positive feedback of drought on heat [ABSTRACT FROM AUTHOR]