Evaluating Compound Flood potential in Indian Estuaries under Non-Stationary Climate Conditions

Climate change and anthropogenic influences alter the primary flood drivers, such as sea surge, rainfall, and river flow, leading to shifts in flood risk patterns. The traditional assumption of stationarity in flood risk assessments is increasingly inadequate, as it fails to account for the dynamic interactions between these drivers. This study presents a framework to evaluate the potential for compound floods under non-stationary conditions, which considers the changing dependencies and risks between sea surge, river flow, and rainfall. The framework employs dynamic copulas to capture time-varying relationships and assess the compounded risk of multiple flood drivers.

The proposed model is applied to Indian estuaries, focusing on east- and west-flowing rivers contributing to the Arabian Sea and the Bay of Bengal. By examining flood events in these regions, the study demonstrates how the potential for compound flooding is amplified under non-stationary conditions compared to traditional stationary assumptions. The results reveal that the compound flood potential increases by 11% to 18% across Indian estuaries, indicating heightened vulnerability to extreme flooding events. This finding underscores the need for updated risk assessments that incorporate non-stationarity, particularly for coastal regions, where the interplay of climatic and hydrological variables is increasingly complex.

The study highlights the importance of adopting non-stationary models for flood risk evaluation in light of changing environmental conditions. By integrating dynamic copula-based approaches, this research offers a more accurate and practical framework for understanding and mitigating compound flood risks in the context of climate change.