Study on the effect of underlying surface changes on runoff generation in the urbanized watershed

In order to address the problem of coordinated flood forecasting in the urbanized watershed, this study proposes a framework for discriminating easily occurring runoff component, which considers vertical spatial heterogeneity based on soil type, land use type and topographic slope, and integrates a Grid-based Runoff Generation Model (GRGM). Taking the control watershed of Jialu River at Zhongmou station (including the central city of Zhengzhou) as the study area, on the basis of GRGM model tests based on 11 observed rainfall-runoff events, the spatial and temporal evolution of runoff components in the study area from 1980 to 2020 and their correlation with the underlying surface changes are explored. The study reveals that: (a) the average relative error of the runoff generation calculation by GRGM model in the study area is reduced by 27.76% and the average coefficient of determination is increased by 0.11 compared with Horton Infiltration (HI) model, which means GRGM model are more accurate. (b) The percentage of excess surface runoff (R_s) in the central city increased significantly from 22 to 67%, and showed a trend of expansion from the central city to the suburbs. (c) The land use types have changed significantly, mainly manifested as a substantial reduction of cropland and a sharp expansion of construction land. R_s is significantly positively correlated with construction land, and the Pearson correlation coefficient exceeds 0.93. The study findings can serve as a scientific basis for coordinated management of flood prevention and disaster reduction in the urbanized watershed.