Compound risks of floods and droughts over multi-hazard catchments: Revealing association through hydrodynamic-cum-statistical modelling and novel bivariate risk classifier.

Floods and droughts are signature phases of the same hydrological cycle. Despite their profound impacts on the socio-economic structures and population globally, limited research efforts have encapsulated the resultant compound risks from them. Comprehending both water extremes presents a formidable challenge due to the relatively short-term occurrence of floods versus the prolonged impacts of droughts. The present study, for the first time in the context of global disaster risk reduction, develops a comprehensive framework driven by a novel concept of Bivariate Risk Classifier (BRC) that can readily integrate the marginal and compound impacts/hazards of floods and droughts. The study employs an exhaustive hydrodynamic-driven approach through LISFLOOD-FP and statistical modelling in terms of the Standardized Precipitation Evapotranspiration Index (SPEI), to derive compound flood and drought hazards. A series of extensive calibration and validation tests ensures minimal false alarms and inaccuracies in the simulated outputs. In the latter phase, populations and regions that are vulnerable to compound risks are identified. This study notices a high degree of synchronization of the exposed population to compound hazards that are otherwise associated with either floods or droughts. The efficient demonstration of the proposed framework over a highly disaster-sensitive catchment in India promises its further application to global multi-hazard catchments. The findings from this study call for an integrated approach directed towards targeted, adaptive disaster risk management and resilient infrastructure planning for regions facing concurrent flood and drought impacts.