A statistical framework for compound pluvial–fluvial flood risk assessment

Abstract

This study introduces a statistical framework for compound pluvial–fluvial flood (CPFF) risk assessment by utilizing a block maxima approach to detect extreme events. The compound flood events are identified by employing lag time analysis of extreme rainfall vis-à-vis extreme streamflow. Bankfull discharge is adopted as a threshold to filter fluvial floods to overcome the drawback of the block maxima approach. The behaviour of these flood pairs is modelled using copulas to estimate the joint return periods of CPFF events for the conjunction and disjunction cases. The framework is applied to the monsoon-dominated Tapi River basin in India. Results highlight the role of monsoon rainfall, pre-saturated conditions, and hydrodynamic responses in amplifying compound flood risks. The upstream catchments in the basin exhibit weaker synchronization of pluvial and fluvial floods than the downstream ones. Higher CPFF risks are observed in the downstream Tapi basin, which is often undermined in a univariate assessment. © 2025 IAHS.