Enhancing residual flood risk assessment through response capacity quantification: Case study of the Sefidroud river, Iran

This study develops a response-adjusted flood risk assessment framework that incorporates physical accessibility to emergency services as a first approximation of community mitigation capacity. The framework is applied to three reaches of the Sefidroud River in northwestern Iran, a region frequently affected by severe flooding. Flood hazard was estimated using the HEC-RAS hydraulic model by integrating water depth and flow velocity across return periods from 2 to 1000 years, while vulnerability was assessed by overlaying land-use exposure with flood damage functions. A response factor—based on proximity to ten critical infrastructures including transport routes, emergency facilities, and healthcare services—was used to represent the accessible component of response capacity in a data-scarce setting. The resulting hydraulic simulations were validated qualitatively against available geomorphological evidence, as quantitative flood-extent data for these extreme return periods was not available. Incorporating this factor reduced the residual risk by approximately 7 % for the 100-year flood and 1 % for the 1000-year flood, indicating the limited moderating influence of local accessibility under extreme events. This work demonstrates how response-related indicators can be integrated into the conventional hazard–exposure–vulnerability paradigm, and outlines a pathway for expanding the framework to include broader social and institutional dimensions in future research. • Integrated response capacity into a residual flood risk framework. • Included human mitigation and emergency response as operational factors. • Modeled 2–1000-year floods in Sefidroud River using HEC-GeoRAS. • Response factors improve risk estimation by linking hazard and preparedness. • Supports Sendai Framework priorities for preparedness and recovery.