The influence of urban expansion on the flood hazard in Santiago de Chile

Land-use changes associated with urban expansion frequently lead to an increase of hazards, both natural and man-made. The process of urbanization is often associated with land-use and land-cover (LULC) changes, leading to a reduction of the infiltration capacity of newly urbanized soil. The goal of this study is to analyze the influence of urban growth on the flood hazard in the case of Santiago de Chile. Therefore, the hydrological model HEC-HMS (Hydrologic Engineering Center - Hydrologic Modeling System) is applied to model the hydrologic system at two time steps. The model allows balancing rainfall and runoff with respect to land use characteristics. A comparison with existing flood hazard maps created based on information of previous floods in Santiago can be used for validation. After successful modeling, i.e. representation of the functioning of the river ecosystem, alternative land-use scenarios can be created to predict the influence of urban land-use / land-cover changes on flood hazard. As a first step, the land-use patterns from 2002 and from a comparative date in 1993 have been delineated from high and very high resolution satellite data (Landsat/SPOT, ASTER) using pixel-based analysis. With this methodology, land-use changes of classes with common hydrological properties could be detected and a first quantification could be achieved. Measured rainfall and runoff data for the past 30 years have been analyzed to investigate the changes in precipitation and runoff characteristics. Finally, precipitation and runoff values are related to land-use changes applying the hydrological model. Applying this approach, the influence of land-use types and their spatial pattern on the runoff characteristics in a sub-catchment is investigated. The application of the hydrological model will help to develop scenarios that can be used to estimate the reaction of an urban environment to extreme rainfall and to suggest improved land-use planning in order to mitigate the flo- od hazard. Future land-use scenarios can be simulated with respect to their influence on the storm water behavior once the model is calibrated.