Effects of different methods for estimating impervious surface cover on runoff estimation at catchment level

One of the most obvious effects of urbanization is an increase of impervious surface cover. Surface imperviousness has an important impact on hydrology, stream water quality and ecology, and is often used as an overall indicator of the health status of urbanized watersheds. It has also been identified as one of the key factors in the occurrence of flash floods. This paper examines the impact of different methods for estimating impervious surface cover on the outcome of a distributed rainfall-runoff model for the upper catchment of the Woluwe River in the southeastern part of Brussels. The study shows that mapping of impervious surface distribution, using remotely sensed data, produces substantially different estimates of discharge at catchment level than traditional approaches that are based on expert judgment of average imperviousness for different types of urban land use. Little difference is observed between results obtained with detailed impervious surface maps derived from high resolution satellite data and sub-pixel estimates of imperviousness derived from medium resolution data. This demonstrates that sub-pixel classification may be an interesting alternative for more expensive high resolution mapping of imperviousness for rainfall-runoff modeling at catchment level.