Uncertainties in Future Extreme Drought Characteristics Associated with SSP Scenarios over Global Lands

This study used the Standardized Precipitation Evapotranspiration Index (SPEI) to identify future global-scale extreme droughts showing less than − 2 of SPEI for four Shared Socioeconomic Pathways (SSP) and 14 Coupled Model Intercomparison Project (CMIP)6 General Circulation Models (GCMs). Afterward, the changes in the projected future extreme drought characteristics were explored using the concepts of Extreme Drought Period (EDP), Extreme Drought maximum Duration (EDD), and Extreme Drought-fed Area (EDA). Furthermore, this study used Reliability Ensemble Averaging (REA) to quantify uncertainties for three drought characteristics. As a result, the historical EDP, EDD, and EDA of GCMs were underestimated compared to CRU with average differences of 0.52, 2.57, and 5.89, respectively. The extreme droughts were projected to occur across all continents and timescales, and EDPs of SSP5-8.5 were higher than in other scenarios by 144% to SSP1-2.6, 76% to SSP2-4.5, and 27% to SSP3-7.0, respectively. The EDA was projected to increase with higher greenhouse gas (GHG) concentrations, and EDA in African continent was larger than different continents by 4% (South America), 18.3% (North America), 10.8% (Europe), 10.2% (Asia), and 8.4% (Oceania), respectively. The uncertainty of the EDP calculated for the historical period is low, with a mean bias term ( \(\:{R}_{B}\) ) of 0.54, whereas the EDP projected for the future indicates higher uncertainty, with a mean convergence term ( \(\:{R}_{D}\) ) of 0.21. In contrast, the uncertainty of the EDD is low for both future and historical periods, with \(\:{R}_{B}\) and \(\:{R}_{D}\) values of 0.92 and 0.98, respectively.