A procedure for estimating hydrological parameters is presented which combines a) remote sensing and GIS techniques with b) data extracted from site visits to city districts; the estimate so obtained is compared with estimates from rainfall data. It is developed in urban sub-basins of Dilúvio Basin in the metropolitan region of Porto Alegre, Brazil. A Fuzzy Algorithm which performs within sub-pixel level is used. Cover classes studied are: highly and slightly impervious, bare ground, grassed open space, and forest. A soil thematic map is determined based on pedological studies. A final distributed thematic map of potential runoff is obtained by superimposing previous data. It is compared with lumped runoff potential from rainfall events in sub-basins. These broad multi-source data hold basic information to develop an alternative strategy for hydrologic studies in urban basins.

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