Assessing Global Drought Trends Under Climate Change: A Comparative Analysis of Four Drought Indices Across SSP Scenarios

Abstract

As climate change intensifies, global droughts are becoming more frequent and severe, making the assessment of future drought trends essential for disaster risk reduction and adaptation. This study examines the spatiotemporal patterns of global drought over the historical period (1850–2014) and under four Shared Socioeconomic Pathway (SSP) scenarios (2015–2100), using a multi-model ensemble of up to sixteen CMIP6 models and four drought indices: the Standardized Precipitation Evapotranspiration Index (SPEI), the Temperature Condition Index (TCI), the Drought Severity Index (DSI), and the Standardized Soil Moisture Index (SSMI). Within the CMIP6 modelling framework and index formulations adopted here, DSI and SSMI showed greater temporal consistency than SPEI-12 and TCI in representing drought evolution. DSI responded more strongly to changes in temperature and precipitation, suggesting its potential usefulness for characterizing short-term dry conditions in temperate and subtropical regions. SSMI, by contrast, responds to soil-moisture variations and shows an amplification of spatial drying and wetting tendencies under higher-emission scenarios. Under high-emission scenarios, extreme drought areas expand rapidly, whereas low-emission scenarios slow their intensification. The complementary information provided by DSI and SSMI may improve our understanding of projected drought conditions within the adopted CMIP6 framework, particularly in southern North America, northern South America, Africa, eastern Australia, and southern China. These findings may inform model-based drought assessment, while implications for operational monitoring require independent evaluation.