Effect of seasonal land use cover from satellite data on surface runoff in two Mediterranean catchments.

In this paper remotely sensed images and ancillary data are used to assess the spatial distribution and seasonal variation of the SCS - Curve Number (CN) parameter(USDA, 1985) within a watershed. Two watersheds were considered in Thirrenian Liguria (North - Western Italy): Bisagno and Entella river. Two Landsat - 5 Thematic Mapper scenes were acquired during different season: late winter and late spring. A Supervised Maximum Likelihood Classification technique was used to obtain a land use map for the two catchments. To characterize the effect of the different surface condition within a watershed in relation to their hydrologic condition, the status of vegetation cover was analyzed in the two seasons. Seasonal variation was described through the evaluation of Fractional Vegetation Cover using an empirical relationship tested in a typical Mediterranean area similar to the case study. Land use and status of vegetation cover information were integrated in a Geographical Information System with lithological maps, in order to estimate the CN parameter in a distributed way. Values of spatially distributed CN parameter were evaluated by comparing measured runoff volumes during a storm events with runoff volumes simulated by a physical - based spatially distributed hydrological model.