The use of radar rainfall estimates for hydrologic modeling of flood response in urban drainage basins

摘要

Warm season thunderstorm systems become an increasingly important element of small basin flood response with increasing urbanization. In this paper we have looked at the response of two basins, Baisman Run and Whitemarsh Run, in the Baltimore Metropolitan Area to two distinct warm season thunderstorms. The high resolution (1 km, 5 minute) radar rainfall estimates are used to characterize the spatial and temporal variability of rainfall and as the precipitation forcing for hydrologic modeling of flood response. Storm structure, storm motion and magnitude of rain rates are used to compare and contrast the two storms. It is shown that the radar rainfall estimates capture the space-time variability of warm season thunderstorms at the scales required for modeling of urban flood response. There are striking contrasts in flood response between the urbanized Whitemarsh Run and the forested Baisman Run. Peak discharge in Whitmarsh Run for the 2000 May 13 storm is more than an order of magnitude greater than peak discharge in Baisman Run. The Runoff ratio exhibits the same relationship. The Network Model is a distributed hydrologic model with a Hortonian infiltration model and a network based representation of channel response. High resolution land surface data sets are used to estimate an impervious cover for Whitemarsh Run. Network Model analyses with impervious cover and high drainage density representative of the existing drainage network capture the timing and magnitude of peak response for Whitemarsh Run. Additional model analyses indicate that elaboration of drainage network is as important as the extent of impervious cover in determining the changes in extreme flood response associated with urbanization.