The determination of land degradation risk in a watershed is an important factor in environmental and agricultural land-use planning. The current trend is to analyze the necessary information for land evaluation in a less subjective way and compatible with geoprocessing techniques. However, criteria and parameters used to quantitatively evaluate the land degradation risk at the watershed scale and based on Geographic Information Systems (GIS) still need to be better defined. The objective of this study, conducted in the second semester of 1996, was to elaborate a comparative evaluation method of land degradation risk in the Marins watershed (Piracicaba, state of São Paulo, Brazil), considering different land-use scenarios, using GIS. The degradation risk maps were obtained from decision matrices for the followings scenarios: (a) no vegetation cover; (b) current land-use; (c) single land-use; (d) reallocated land-use; (e) planned use. The results were compared by an index called "Weighted Degradation Risk Index (IP D)". This index allowed quantitative comparison of land degradation risk for the land use scenarios proposed. The results showed that the change in the spatial allocation of land-use was not enough to decrease the land degradation risk, indicating an over-use of the watershed. In order to avoid the impacts caused by this over-use, restrictions on land occupation are necessary. Areas with high erosion susceptibility should be occupied with uses offering better soil protection, resulting in a decrease in the area occupied with annual and semi-perennial crops.
land use planning; erosion; land degradation; environmental impacts; geoprocessing; watershed