Southwestern United States drought of the 21st century presages drier conditions into the future

Abstract

Intense drought has occurred in the United States Southwest this century, causing unprecedented stress to water resources. Here we use paleoclimate and instrumental records to establish that the recent temperature rise is incompatible with random draws from past fluctuations, including the current period of warming. Consistent with and extending previous reconstructions, we find that the ongoing drought is the most intense at the 21-year scale back to 600 CE. Evaluation using standardized regression coefficients shows that recent warming damps the effect of moisture delivery on the Standardized Precipitation-Evaporation Index by approximately one-third. The probability of full recovery of the current moisture deficit is unlikely even by mid-century and about five percent in 10-15 years. Evaluation of future climate simulations indicates increasing regional temperature stress and soil moisture depletion, and coupled with long recovery periods for moisture delivery, very low chance for regional mega-reservoirs to regain full-capacity levels assuming current demand.

Increasing prevalence of hot drought across western North America since the 16th century

“…While all evidence therefore suggests that the modern megadrought across much of WNA is an anthropogenically influenced hot drought, (10,15,16,24,28,29), the relationship between temperature and the severity and persistence of past droughts in this region remains almost entirely unknown before the instrumental era. This stems from the comparative paucity of temperature-sensitive tree-ring chronologies in the coterminous United States (30)(31)(32)(33) despite the region having comprehensive paleoclimate evidence of hydroclimate variability over the past millennium (25).…”

Global diagnosis of land–atmosphere coupling based on water isotopes

“…Semi-arid and arid continental climates dominate in the Great Plains. Droughts further threaten water availability in the region 52 – 54 . During our observation period, mega-droughts happened in the Southern United States, which could induce soil moisture depletion.…”

Past and Projected Future Droughts in the Upper Colorado River Basin

“…Much of the western United States (U.S.), including the UCRB, has been in drought conditions since the year 2000 (McCabe & Wolock, 2021;Wahl et al, 2022;Williams et al, 2020Williams et al, , 2022. The drought has been driven by precipitation deficits across a large part of the western U.S. since the year 2000 and also by positive temperature anomalies across the western U.S. which have been attributed to global warming (Williams et al, 2020(Williams et al, , 2022.…”

“…The 2000–2021 UCRB drought is considered the worst UCRB drought since 1900 (Udall & Overpeck, 2017)—possibly one of the worst droughts in at least the past 12 to 14 centuries (Wahl et al., 2022; Williams et al., 2022), but it is not the most severe drought in the past 2,000 years (Gangopadhyay et al., 2022b). Given that warming temperatures are exacerbating UCRB droughts (Woodhouse et al., 2016), we (a) use a paleoclimate reconstruction of UCRB streamflow to examine drought characteristics (e.g., mean streamflow departure and length) in the UCRB during multiple centuries, (b) place the UCRB drought during 2000–2021 in the context of droughts that occurred over multiple centuries, and (c) address the possible effects of increases in temperature on UCRB drought.…”