Evaluating the effects of single and integrated extreme climate events on hydrology in the Liao River Basin, China using a modified SWAT-BSR model

Extreme climate events may have a substantial impact on water conservation in the black soil region of China. This study integrated a dynamic CO2 input method and an alternative freeze-thaw cycle function into Soil and Water Assessment Tool (SWAT) to create a SWAT-Black Soil Region (SWAT-BSR) model. The SWAT-BSR model was used to simulate extreme climate events in the Liao River Basin (LRB; 220,000 km2) and an R script was developed to extract days in which extreme climate events occurred along with corresponding hydrological variables. Extreme climate events included extreme heat, cold, precipitation, and drought events across seven zones in the LRB. Subsequently, we explored the changes in single and integrated extreme climate events during the historical period (1971-2000) and future periods (2041-2070 and 2071-2100) under the SSP2-4.5 and SSP58.5 scenarios. The results indicated that almost each hydrological variable was reduced under extreme cold and drought events compared to the normal conditions in the historical period. Canopy interception and percolation were decreased under extreme heat in the future periods while extreme cold was opposite with a pronounced negative impact on reference evapotranspiration and soil evaporation. In contrast, each hydrological variable under extreme precipitation increased relative to the normal conditions while hydrological variables were largely negatively affected under extreme drought. In addition, the integrated extreme climate index increased over time, with more pronounced changes under the SSP5-8.5 scenario than those of SSP2-4.5 scenario. Hydrological variables were most at risk in the dryland zones as compared to partially irrigated and irrigated zones. These findings indicated that more attention should be given to the impacts of extreme climate events on water losses from both historical and future perspectives. It is also necessary to develop mitigation strategies for water conservation in the LRB based on the extreme climate events projected to occur in different zones and periods in the future.