Assessing global drought conditions under climate change: A comparison of stationary and non-stationary approaches and identification of hotspot regions

Droughts pose significant threats to both human society and the surrounding environment. Because of the anticipated intensification of drought conditions owing to climate change, assessing their impacts using dynamic and non-stationary methodologies is considerably required. This study employed temperature and precipitation data derived from a comprehensive set of 15 global climate models (GCMs) under two shared socioeconomic pathways (SSP2-4.5 and SSP5-8.5) within the framework of the Coupled Model Intercomparison Project Phase 6 (CMIP6) dataset to address crucial inquiries related to drought. Specifically, we explored the transformations that drought conditions may undergo with increasing temperature and precipitation levels. The study identified geographical areas likely to become hotspots of global warming and compared drought indices that incorporate non-stationarity with those that do not in assessing the evolution of global drought conditions. The findings revealed that indices using stationary approaches with fixed distribution parameters underestimate or overestimate future drought conditions because they overlook trends such as decreasing precipitation and increasing temperatures in drought variables. This results in an average misestimation of approximately 10 %-20 % in duration and severity in the far future in the sub-regions. Specifically, underestimations were detected in the high latitudes of the Northern Hemisphere (Alaska and Northern Asia), northwestern China, India, and northern and eastern Africa. Conversely, the stationary drought index exhibited maximum overestimations in the Amazon, Western Australia, the Mediterranean region, and South Africa regions for future drought projections. Combining the results of the multi-drought characterization, including frequency, duration, severity, and spatial extent, we identified Northern North America, the Amazon region, the Mediterranean region, south-central Africa, and southeastern Asia as hotspot regions for drought responses to global warming. In future drought warnings, particular attention should be directed toward regions where drought is underestimated.