The US Southwest is experiencing a severe drought. While climate change increases evaporative demand and reduces water supply, this study shows that cooler tropical Pacific sea surface temperatures (SSTs) reduced cool-season precipitation, driving a decline in soil moisture. Projections to 2040, accounting for natural decadal variability and forced change, indicate that Pacific and Atlantic Ocean variability will significantly impact future drought conditions. The worst-case scenario involves a continued cold tropical Pacific and warm Atlantic, while the best-case scenario involves a warm tropical Pacific and cold Atlantic. Radiatively-forced precipitation reduction is most pronounced if the equatorial Pacific cold tongue remains unwarmed. Regardless of these variations, a return to late 20th-century precipitation and soil moisture levels is unlikely.

Richard Seager, Mingfang Ting, Patrick Alexander, Haibo Liu, Jennifer Nakamura, Cuihua Li, Matthew Newman