A unified runoff generation scheme for applicability across different hydrometeorological zones

Runoff generation in humid and semi-arid regions are usually dominated by saturation-excess mechanism and infiltration-excess mechanism, respectively. However, both mechanisms can co-exist in semi-humid regions. Therefore, we proposed a unified runoff generation scheme to represent the single and mixed runoff generation processes, making it applicable for different hydrometeorological conditions. The saturation-excess runoff generation scheme of the Xin'anjiang model was integrated with a modified Horton infiltration scheme at the grid cell scale. By substituting the original runoff generation scheme of the grid-Xin'anjiang (GXAJ) with the integrated scheme, we developed a new distributed hydrological model called grid-Xin'anjiang-infiltration-excess (GXAJ-IE) model. GXAJ-IE was tested in four watersheds and compared with two benchmark models with single runoff generation mechanism. The results indicate that GXAJ-IE model has higher flexibility and robustness in reproducing flood hydrographs under different rainfall conditions in semi-humid watersheds and has comparable performances with the benchmark models in humid and semi-arid regions.