Investigation into the transforming mechanism from flash-to-conventional drought in different soil moisture layers in a highly climate-diverse basin

Study region The Indus Basin, a highly diverse climate basin in South Asia. Study focus The transformation from flash drought to conventional drought (FD-CD) poses significant challenges to drought risk and management systems, necessitating a comprehensive assessment of the dynamics involved. Previous studies focused on the FD-CD process solely through the perspective of the recovery phase, overlooking the persistent phase between drought onset and recovery. This study aims to determine which phase of drought contributes the most to FD-CD and explore the impact of various climate characteristics on this phase. New hydrological insights We found that FD-CD is more likely to occur in deeper soil moisture layers, particularly in semi-arid and arid regions of the Indus Basin, with its peak period from July to October. The persistent phase of drought is most significant contributor to FD-CD development, with an average duration of 13 octads, significantly longer than the recovery phase (~ 5 octads), while the average rate of soil moisture change is relatively low during the persistent phase (0.025%) compared to the recovery phase (0.08%). XGBoost SHAP analysis reveals significant differences in the contribution of meteorological variables to the persistent phase in various climate zones. The contribution of high temperature to the persistent phase is most significant in the arid zone, while precipitation deficit is a dominant associated factor in other climate zones of the study domain. These findings contribute to understanding the FD-CD dynamics, providing new insights into the importance of the persistent phase in the life expectancy of the FD.