Scale-dependent flood response to land use dynamics in the Jinxiuchuan Reservoir watershed, China

Jinxiuchuan Reservoir watershed (JRW), located in the southern mountainous area of Jinan City, Shandong Province, China. This study investigates the flood response to land use/land cover (LULC) changes in the JRW. Using the distributed HEC-HMS hydrological model, flood simulations were conducted at both the watershed and sub-watershed scales under four LULC scenarios for 1990, 2000, 2010, and 2020, quantifying the impacts of urbanization-induced LULC changes on flood volume and peak discharge. The results reveal distinct differences in the response magnitude of floods of different sizes under LULC changes, as well as pronounced spatial heterogeneity at the sub-watershed scale. At the watershed scale, LULC changes exert the strongest influence on small-volume and small-peak floods, while large-magnitude floods show weaker responses. At the sub-watershed scale, the southern sub-watersheds exhibit stronger responses due to more substantial land cover changes. Additionally, CN values and impervious surface ratios show overall significant positive correlations at the watershed scale, with stronger relationships for small- and medium-magnitude floods, but weaker for large floods. In sub-watershed W410, a localized deviation was observed, characterized by a slight increase in impervious surface ratio and a marginal decrease in CN, which is consistent with the spatial heterogeneity of hydrological responses under mixed land surface conditions. • Simulated flood response under four LULC scenarios using the HEC-HMS model. • Urbanization-induced land use changes increased flood volume and peak flow. • Small floods are more sensitive to land use changes than large floods at multiple scales. • CN and imperviousness are strongly correlated with flood metrics at multiple scales. • Findings support fine-scale flood risk assessment and urban watershed planning.