GIS - based Flood Risk Analysis Across Large Metropolitan Areas

This paper examines the effects of urbanization on the flood hazard in semi-arid/arid southern California using traditional hydrograph, frequency-magnitude and statistical analysis augmented with GIS-based variable parameterizations and visualizations. It was found that the peak flood discharges were significantly increased in urban watersheds in conjunction with increasing mean baseflow in the streams. Urbanization resulted in a reduction in flood duration and the number of days of storm flows after the peak discharge. The rainfall-runoff relationship has also changed in urban watersheds and showed certain patterns across the watersheds over time. This research shows how GIS can serve as a platform for characterizing the cumulative impacts of neighborhoodspecific land use changes and stream modifications on the flood hazards by estimating hydrologic parameters and integrating different types of spatial data sources. It concludes that floods behave differently in urbanized watersheds and non-urban watersheds.