An analytical study on the influence of initial soil moisture and meteorological anomalies on flash droughts

Study region The study focusses on 13 major watersheds of India. Study focus Rapid depletion of soil moisture during flash droughts is influenced by complex interactions between initial soil moisture and anomalies in meteorological variables. In this study, numerical experiments are conducted on an analytical land-atmospheric model to gain a conceptual understanding of the influence of initial soil moisture (SM) and meteorological anomalies on flash droughts. The analytical model is calibrated using reanalysis dataset and validated with remotely sensed surface soil moisture. Numerical experiments are conducted on the calibrated model by perturbing the soil moisture at the onset of flash drought events and its impact on flash drought severity are analysed. New hydrological insights for the region It is found that the influence of meteorological anomalies decreases with initial soil moisture in majority of monsoon season flash droughts in humid, sub-humid and semi-arid regions. In these flash droughts, precipitation anomalies are the major contributors to flash droughts. On the other hand, the influence of meteorological anomalies increases with initial soil moisture in flash droughts of arid regions. In these flash droughts, soil moisture depletion is primarily driven by precipitation anomalies in dry antecedent conditions and jointly by precipitation and potential evapotranspiration anomalies in wet antecedent conditions. The insights gained from the analysis highlight the need to use region- and season-specific predictors for accurate prediction of flash drought severity.