Record Low North American Monsoon Rainfall in 2020 Reignites Drought over the American Southwest Bulletin of the American Meteorological Society

Drought has plagued the American Southwest since 2000, leading to the second lowest estimated 19-yr average soil moisture in approximately 1200 years (Williams et al. 2020), fueling destructive wildfires (Fu et al. 2021) and inducing low flows in major rivers (Udall and Overpeck 2017; Hoerling et al. 2019). In 2020/21, drought deepened against the backdrop of two decades of accumulated drought damages that exceed $131.4 billion (NCEI 2021) and caused alarm about potential water delivery shortages in the Colorado River basin (U.S. Bureau of Reclamation 2021). The proximate causes for persistent regional droughts include low precipitation (Lehner et al. 2018) and increased evaporative demand in concert with warming temperatures (Crockett and Westerling 2018; Williams et al. 2020). While there is strong evidence for anthropogenic forcing of the warming trend (e.g., USGCRP 2018), recent work has also pointed to a potential human effect on Southwest precipitation (Pascale et al. 2017; Hoerling et al. 2019; He et al. 2020).