Projections of the characteristics and probability of spatially concurrent hydrological drought in a cascade reservoirs area under CMIP6

Improving the understanding of the future hydrological drought variability in cascade reservoirs area is indis-pensable for water resource management, especially in the context of changing climate. This study aims to investigate the hydrological drought variations in the upper Yellow River Basin (UYRB) during 2021-2100 employing the latest Coupled Model Intercomparison Project Phase 6 (CMIP6) datasets. The study area is divided into three sub-regions based on the location of the two large reservoirs, i.e., Region 1 (R1) and Region 2 (R2) have reservoirs while Region 3 (R3) has none. The meteorological data from 10 CMIP6 models are downscaled by utilizing the bias-corrected spatial disaggregation (BCSD) method and then used to force the improved abcd hydrological model for future monthly runoff simulations. The changes in severity, duration, and frequency of drought events in three sub-regions under two future climate scenarios (SSP2-4.5 and SSP5-8.5) relative to the historical period are identified. Then, the copula function is applied to explore the changes in probabilities of spatially concurrent drought for different cases in the future. The most likely combination of drought intensity for R1 and R2 corresponding to 10-years conditional return periods is estimated to demonstrate changes in drought risks across the reservoir areas. Results show that the drought frequency of R2 and R3 is expected to increase in spring and summer, and the drought events are projected to have a shorter duration and lower severity overall under two scenarios. Additionally, the spring probabilities of concurrent drought for different cases are expected to increase in the near future (increase by 1.9%-19.3%), but only increase in R2&R3 case in the far future. It is noted that although the drought probabilities will decrease in winter, R1 and R2 are expected to experience more severe drought when drought occurs in R3. The findings are helpful to improve the under-standing of future hydrological drought risk in the UYRB and provide guidelines for making adaptation strategies to climate change.

Automated summary

This study investigates the future hydrological drought variations in the upper Yellow River Basin using CMIP6 datasets. The findings suggest that the frequency of drought events is expected to increase in certain regions during spring and summer, but the overall severity and duration of droughts are projected to decrease. The spring probabilities of concurrent drought events are also expected to increase in the future, with a higher increase in certain regions.