Understanding Drought‐Induced Soil Moisture Feedback on Atmospheric Circulation: Observations and Simulation Experiments of the 2020 Western U.S. Drought

Abstract This study examines the large‐scale atmospheric response to reduced evapotranspiration during droughts in the Western U.S., using an observation‐based regression method and numerical experiments with a global climate model. We found that Western U.S. droughts are generally associated with an anomalously strong ridge that displaces the storm track, leading to fewer incursions of transient upper‐level disturbances (less Eddy Kinetic Energy (EKE)) into the Western U.S. in summer and fall. We examined the simulated local and remote influences of sea‐surface temperature (SST) and soil moisture depletion during the development of the 2020–2021 drought. The numerical experiments in the Community Earth System Model (CESMv2) show that anomalously low soil moisture leads to reduced evapotranspiration, warming of the surface and strengthening of the ridge over the Northern U.S. during the late‐summer. Similar to the observational regression, the modeled 2020–2021 summer drought response displaces the storm track, reduces EKE in the Western U.S., and leads to the generation of Rossby waves that affect remote circulation. A nearly circumglobal response to summer drought was found in geopotential and zonal winds, suggesting a poleward displacement of westerlies. In fall and winter, the response to SST was stronger and dominated over that of soil moisture, while soil moisture was itself less strongly coupled to evapotranspiration. Despite the larger role of SST during winter, there was a constructive effect of SST and soil moisture anomalies on the large‐scale global wave pattern, with similar positive geopotential anomalies over the Atlantic and western Asia, and negative anomalies over western Europe.