Hydrologic Responses to Urbanization Patterns

Abstract:

This study investigates the hydrologic responses to urbanization as well as the potential surface-atmosphere feedback related to urban processes. The shift of spatial rainfall patterns is a detectable overlying change induced by the feedback. A hypothetical urbanized watershed was configured by simplifying rainfall-runoff processes in real urban watersheds. Forty-eight scenarios were simulated with different spatial patterns of rainfall and impervious coverage considered. Hydrologic responses were analyzed with four metrics--flow distribution, daily variation, frequency of floods and interannual runoff variability, as well as the relative changes in flood magnitudes for different scenarios. Results indicate that the variations of four hydrologic metrics do not present monotonic trends with the increase of impervious coverage as described in previous studies, but depend on the spatial extent of urban coverage and the spatial patterns of rainfall. The largest hydrologic variations and relative changes of flood magnitudes occur when the watershed is moderately urbanized (with 20~30% impervious coverage). Changes in flood magnitudes induced by urbanization could be underestimated by almost 50% if the spatial rainfall patterns are not considered. We attribute the most detectable hydrologic variations to the heterogeneous properties of the underlying surface and the coincidence of spatial patterns of rainfall with impervious coverage. This study reassessed the hydrologic responses to urbanization considering both the changes of impervious coverage and spatial rainfall patterns, and highlighted the necessity of considering comprehensive assessments in future urban planning.