Mapping of Environmental Fragility in the Aldeia Velha River Basin, State of Rio de Janeiro, Brazil

This paper presents an approach to mapping the environmental fragility of river basins. The study was performed at the Aldeia Velha river basin, a rainforest watershed located between Rio de Janeiro's coastal plains and the Serra do Mar highlands. A multiple-criteria analysis was performed involving factors that affect the risk of erosion; these variables were analyze using GIS tools and were integrated by algorithm in order to form a description of the different classes of environmental fragility in the basin. The multicriteria analysis considered the use of a numerical land model, official data, orbital imagery and the opinion of subject-matter experts. A Map of Potential Fragility (MPF) was generated through the collection of secondary information such as soil types, rainfall intensity and terrain slope. This initial map was later combined with a land-use projection to produce a Map of Emerging Fragility (MEF). The mapping results pointed to a highly fragile environment, where more than 70 percent of the basin's area was classified with high or very high degree of fragility, in both the potential and emerging context. The Apparent Erosion Processes (AEP) were positively correlated in the areas with a higher level of fragility in the final map products, as well as highlighted the locations most prone to the intensification of erosion processes. The models generated important information for land-use planning, enabling affordable and easy upgrade for municipal governments and civil society organizations to monitor high fragility areas.