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Runoff, hydrologic response unit, curve number, land uses, GIS, DEM


The Rio San Pedro sub-basin runoff was estimated using the curve number method (NRCS-CN) applied to hydrologic response units (HRU’s), derived from remote sensing and GIS analysis. The sub-basin (around 2900 km2) was delineated from digital elevation models (DEM), that also were used to obtain the slopes in the study area. A landscape characterization (overall accuracy > 80%), based on Landsat ETM+ imagery, was obtained using standard classification methods, and together with a rainfall data series, were the input information for the sub-basin discretization in HRU’s and the runoff calculation. Seventeen HRU’s were obtained, that can be arranged in three main groups. HRU’s associated to forest and high relief areas, representing 2/3 of the total area and contributing up to 71% of total runoff. The land covers related with human activities integrate a second HRU’s group, contributing with 20% of runoff, although they represent less than 15% of the area. Finally wetlands and aquatic surfaces, not contributing to runoff, are the third HRU group. Because of the measures of accuracy correspond to good agreement between the model and the reference data, the HRU’s approach that retains the spatial heterogeneity, is considered a fine approximation for the San Pedro sub-basin runoff assessment that can be integrated to the development of environmental management programs.