Potential Near‐Term Wetting of the Southwestern United States if the Eastern and Central Pacific Cooling Trend Reverses

• Published in: Geophysical research letters Vol. 51; no. 13
• Main Authors: Alessi, Marc J., Rugenstein, Maria
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16-07-2024; Wiley
• Subjects: Anthropogenic climate changes; Anthropogenic factors; Climate change; Climate models; Climate prediction; climate projections; Climatic evolution; Cooling; Drought; Drought conditions; Drying; Error analysis; Global warming; Green's function; Green's functions; Human influences; Precipitation; Precipitation trends; Sea surface temperature; Sensitivity analysis; Surface temperature; Trends; uncertainty; Wetting; United States > US
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL108292

Near‐term projections of drought in the southwestern United States (SWUS) are uncertain. The observed decrease in SWUS precipitation since the 1980s and heightened drought conditions since the 2000s have been linked to a cooling sea surface temperature (SST) trend in the Equatorial Pacific. Notably, climate models fail to reproduce these observed SST trends, and they may continue doing so in the future. Here, we assess the sensitivity of SWUS precipitation projections to future SST trends using a Green's function approach. Our findings reveal that a slight redistribution of SST leads to a wetting or drying of the SWUS. A reversal of the observed cooling trend in the Central and East Pacific over the next few decades would lead to a period of wetting in the SWUS. It is critical to consider the impact of possible SST pattern trends on SWUS precipitation trends until we fully trust SST evolution in climate models.
Plain Language Summary
Precipitation trends in the southwestern United States (SWUS) are sensitive to the pattern of sea surface temperature (SST) trends in the Tropical Pacific. Since the turn of the century, a decrease in SWUS precipitation has been linked to a cooling of the Central and Eastern Pacific (1990–2020). Notably, climate models are unable to simulate this observed cooling SST trend. In this study, we answer how SWUS precipitation projections may be impacted by potential error in the simulation of future SST trends by climate models. We first demonstrate that slight changes in the pattern of SST trends leads to either a wetting or drying of the SWUS. Second, if the current 30‐year cooling trend in the Central and East Pacific switches to a warming trend, the SWUS could experience a near‐term increase in precipitation. While climate models are the main tool to predict the global response to anthropogenic climate change, we must consider and account for their error in projections of global warming.
Key Points
The observed Equatorial Pacific cooling trend, unpredicted by climate models, may have led to decreased precipitation in the southwestern US
With a sea surface temperature‐precipitation Green's function, we find that small changes in sea surface temperature can either wet or dry the southwestern US
A reversal of the cooling trend in the Equatorial Pacific could lead to a wetting trend in the southwestern US