Identification of dominant flood descriptors and their interaction with watershed morphology in central and southern peninsular regions of India

The hydro-meteorological factors influencing flood timing and magnitude are shifting due to natural and anthropogenic climate change. Regionally, the association between floods and their driving factors/descriptors is complex. This necessitates a deeper understanding of flood generation to enhance forecasting, modeling, and risk analyses—critical aspects of effective flood management. Thus, to better understand flood generation in India, we investigate the dominant flood-generating descriptors and their relationship with watershed characteristics across central and southern peninsular India using circular statistics. We find that flood generation is primarily influenced by soil moisture and precipitation excess, dominating 89% of the analyzed (231) watersheds. In particular, larger watersheds (>70000 km ^2 ) are predominantly influenced by soil moisture, while smaller ones (<16000 km ^2 ) are influenced by precipitation. Interestingly, watersheds covering similar areas produce higher flood flows if predominantly influenced by soil moisture. The explicit evaluation suggests a positive influence of antecedent soil moisture (ASM) on flood flows across all watersheds. An attempt to relate the morphological characteristics with flood descriptors reveals a positive (negative) influence of the topographic wetness index (TWI) on annual maximum flows for soil moisture-dominated (precipitation-dominated) watersheds. This indicates that ponding/accumulation is a driving (limiting) factor for soil moisture (precipitation) dominated watersheds. The relative importance of the ASM compared to precipitation decreases when the precipitation intensity (PI) increases, implying exchanges of influence at certain levels of PI. Further exploration could reveal insights into the interplay between ASM and precipitation, crucial for flood magnitude and hazard assessments. Given that flood behavior is significantly influenced by dominant descriptors, it is advisable to adopt a segregated approach in analyzing flood escalation under climate change. In addition, incorporation of dominant flood descriptors into cascade flood modeling is essential for enhancing flood hazard and risk modeling.