Proposta metodológica para identificação de áreas prioritárias para recomposição florestal – estudo de caso: bacia hidrográfica do rio Macacu/RJ

Abstract

The Macacu river is a tributary of Guanabara‟s Bay and is responsible for water supply of about 2.5 million inhabitants. Despite the evident hydrological and environmental importance the Macacu River basin has been subjected to an intense process of economic growth that can compromise their environmental services, making necessary the establishment of regional planning strategies to obtain a sustainable development. In this sense, the survey of environmental and physical characteristics of the basin, to identify areas with greater vocation for the production of water as well as areas with greater susceptibility to erosion, serves as a subsidy to direct the actions of public policy, optimize the allocation of financial resources and disciplinary uses consistent with the production and water quality. Within this context, this study aims to identify priority areas in the Macacu‟s river basin to be reforested, focusing on optimizing the quantity and quality of water produced. To combine the factors was used multicriteria evaluation (Weighted Linear Combination), using the module MCE (Multicriteria Evaluation) in the software IDRISI. Through this methodology, the factors are standardized to a common numerical scale, receive weights and are combined using a weighted average. The criteria adopted to obtain the final map of priorities were: size of forest fragments; proximity between fragments; vulnerability to erosion, distance to urban centers and road network; morphometric factors, degree of degradation of the watershed (number of degraded areas) and conflicting use into the Areas of Permanent Preservation (APP). After crossing information, the priorities map was reclassified into five classes of priority: very low, low, medium, high and very high. Thirty five watersheds were identified as priority, located mainly in medium and lower sector of the water basin. These watersheds have approximately 9380 ha covered by human activities, especially the pastures that occupy 8746 ha, mostly depleted and degraded. These pasture areas could, by efficient public policies, be indicated to the forest recovery, generating more consistent hydrological results for the region. It could be concluded that the multicriteria evaluation used to define priority areas for forest recovery was adequate for the objective, since the viewing of the final map shown to be effective in the spatialization of the areas most suitable for reforestation projects, serving as decision suport.