Exploring spatio-temporal variation of drought characteristics and propagation under climate change using multi-model ensemble projections

Climate variation is a primary driving force influencing the hydrological cycle, resulting in extreme natural disasters such as drought. Investigating the linkage between meteorological and hydrological droughts under climate change is critical for early warning against hydrological drought. In this study, we investigated spatial and temporal characteristics of the drought propagation threshold (PT) in the Han River Basin (HRB) of South Korea. Standardized Precipitation Index (SPI) and Standardized Runoff Index (SRI) were employed to represent meteorological drought and hydrological drought, respectively. Correlation analyses between the SPI at various time scales (1–24 months) and the three-month SRI (SRI-3) were performed to identify the best time scale of SPI corresponding to the SRI-3. To investigate PTs, five general circulation models (GCMs) were selected to compute multi-model ensemble projections under Representative Concentration Pathway (RCP) 4.5 and 8.5 scenarios. A future period (2021–2099) was sub-divided into two periods such as P2 (2021–2060) and P3 (2061–2099) to estimate temporal variation of PT. Our results indicated that the SPI-4 showed the highest correlation with the SRI-3 in P1, while the SPI-3 best corresponded to the SRI-3 in future periods under both climate change scenarios. Drought characteristics of meteorological and hydrological drought showed increasing trends in P2 and P3 under both climate change scenarios. Spatio-temporal variation in PT was observed throughout the HRB. The PT showed significant decreases in both future periods, while the highest percentage decreases were observed in watersheds located in the northern, mid, and western parts of the HRB in P3 under both climate change scenarios.