Understanding Flood Behaviour: The Role of Antecedent Soil Moisture, Rainfall and Catchment Attributes Across Multiple Basins

ABSTRACT This study aims to understand the effect of antecedent soil moisture (ASM) conditions on flood characteristics across nine Indian basins using the Soil Moisture Accounting (SMA) method within the Hydrologic Engineering Center—Hydrologic Modelling System (HEC‐HMS) model. Hypothetical rainfall events representing different scenarios and return periods were generated to assess the combined impact of rainfall, catchment properties, and ASM on flood prediction. The results reveal that while rainfall predominantly influences flood characteristics, ASM conditions also contribute significantly in certain basins. For instance, in the Netravati basin, high rainfall diminishes the impact of ASM on floods, whereas in the Nagavali basin, ASM significantly affects flood characteristics under high‐intensity rainfall due to steep slopes and high infiltration capacity. The Upper Tungabhadra basin shows minimal ASM impact due to its high infiltration and elongated shape, while the Upper Tapi basin experiences significant ASM effects due to lower infiltration capacity. The Upper Mahanadi and Brahmani basins exhibit variable flood responses to ASM, particularly under intense rainfall conditions. In larger basins like the Upper Narmada, Wardha, and Wainganga, the vast area and lower infiltration losses render ASM effects negligible. These findings highlight the necessity of integrating local morphometric, land use, and ASM into flood modelling to improve flood prediction and management.