Remote sensing monitoring of multi-scale watersheds impermeability for urban hydrological evaluation

Urban impervious surface coverage is an important parameter to understand effects of hydro-environment on the process of urbanization. Impervious surfaces have altered urban hydrological process, spatial and temporal distribution of water resources and water environment quality and led to increasing frequency and intensity of urban waterlogging. In view of the impact of the increase of impervious surface on urban hydrological environment, there are two problems in current research and application: (1) urban hydrological modeling and impermeability ratio are computed according to multi-level administrative units rather than watersheds; (2) the entire urban hydrological environment is an organic whole, but the urban watersheds system within a city have not been monitored dynamically by considering adjacent watersheds. In view of these two problems, the main innovative points in this research work include (1) first, urban multi-scale watersheds are defined, and impermeability ratios are calculated at multi-scale watersheds level for urban hydrological modeling. (2) Based on urban DEM analysis, considering the interconnection of multiple urban water systems by calculating the dynamic impermeability ratios, the dynamic impact of urban rainfall and runoff changes on the whole urban hydrological environment is monitored. The results show overall impervious surface ratio of each watershed is proportional to the runoff. The ratio of the impervious surface reaches 20%, and the discharge is more than twice that when impervious ratio is 4%. It can be concluded that at watershed level a higher the degree of urbanization can lead to a larger change in the total run off, and the earlier shift of the peak flow.