Projected Evolution of Droughts and Human Exposure in the Contiguous United States under SSP5-8.5: A Regional Downscaling Perspective

https://doi.org/10.1088/1748-9326/adf4f9
2025-07-28
Environmental Research Letters
Leyuan Zhang, Hannah Rubin, Rong-You Chien, Joshua S Fu, Deeksha Rastogi, Shih-Chieh Kao, Moetasim Ashfaq

The increasingly unpredictable and extreme weather patterns under a warming climate underscore the urgency of accurate regional assessments of future drought risk. This study evaluates the projected drought evolution in the contiguous United States (CONUS) under the high-emission SSP5-8.5 climate scenario for the coming decades. Using a multi-model ensemble of six CMIP6 global climate models (GCMs) combined with dynamical downscaling techniques, we analyzed near-term (2020-2039) and mid-term (2040-2059) drought patterns using the Self-Calibrating Palmer Drought Severity Index (ScPDSI), the Standardized Precipitation Index (SPI-12), and the Standardized Precipitation-Evapotranspiration Index (SPEI-12). Results reveal a widespread increase in abnormally dry (D0) and moderate drought (D1) conditions, particularly in urban areas, while severe (D2), extreme (D3), and exceptional (D4) droughts are expected to become less common in many regions. Meanwhile, persistent and intensifying droughts are projected in the western and southwestern U.S., driven by long-term soil moisture deficits. The ScPDSI projects that 1.1 million urban residents will be affected by D0 conditions in 2050, while SPI-12 suggests a decrease in the total affected population after 2040. ScPDSI indicates prolonged droughts in the West, and SPI-12 captures transient variability. Although the total drought-exposed population is expected to decrease, urban areas will continue to bear a greater burden, particularly for mild droughts (D0, D1). These findings highlight a shift toward more frequent mild droughts, fewer severe droughts, and persistent drying in the Southwest, emphasizing the need for region-specific adaptation strategies.