Emerging Hotspots and Land-Cover Contrasts of Global Compound Droughts (1983–2021)

Understanding the spatial and temporal evolution of high-impact compound droughts, arising from interacting water-supply and atmospheric-demand drivers, is crucial for assessing ecosystem risks under climate change. Here, we analyze global compound droughts from 1983 to 2021 by integrating the Standardized Precipitation Evapotranspiration Index (SPEI) and vapor pressure deficit (VPD), representing water-supply and atmospheric-demand dimensions, respectively. A compound drought event is defined when SPEI < –1.1 and VPD ≥ the 90th percentile within the same grid cell and time period.

Results reveal a significant intensification and expansion of compound droughts over the past four decades. The probability multiplication factor (PMF) between SPEI and VPD exceeds 1 across most subtropical and continental interior regions, indicating strong co-occurrence of soil and atmospheric dryness. Subtropical high-pressure zones (15°–40° N/S)—including southwestern North America, the Mediterranean Basin, southern Africa, and southern Australia—emerged as global hotspots, with 2020 marking the historical peak in affected area.

Distinct land-cover contrasts were also observed. Forests and grasslands experienced the highest exposure frequencies, whereas tundra and cropland were less affected. After 2005, compound drought areas in forests and grasslands expanded markedly, consistent with the global rise in atmospheric aridity. These findings underscore the growing dominance of compound droughts as a global climate hazard and highlight the importance of jointly considering multiple interacting drivers in ecosystem risk assessments and future adaptation strategies.