The present proposal aims to contribute to a scientific evaluation of the results of a public policy of payment for environmental services (PES) implemented in the municipality of Extrema (MG), in headwaters of a contributing basin to the Cantareira System, which is located in the center of discussions on the water crisis in the State of São Paulo. The studies will consider the climate changes projected through mathematical models and respective change scenarios pointed out by researchers from all over the world, seeking to evaluate their impacts on the hydrobiogeochemistry of two small basins, including studies in their spring areas and, scientifically checking the results. expected from the PSA. In this way, the project team will continue to monitor the quality and quantity of its water resources, as well as improve the application of hydrological models at different scales, which consider agricultural practices, changes in land uses, altered vegetation cover of Atlantic Forest, soils and topography, in addition to climate behavior, with regard to hydrological and biogeochemical dynamics, and to guide actions related to environmental management policies in the studied area and the like. In order to achieve the proposed objective, the following specific objectives were defined: (i) To organize an environmental database for the region studied; (ii) Establish monitoring at two sampling stations in the runoff of the two basins to quantify the discharge and characterize the fluvial hydrobiogeochemistry, with complementary laboratory analyses; (iii) Apply the AgES-W and MIKE SHE models to assess the effects of land use changes on water quantity and quality and simulate the combined effects of predicted climate change in order to guide related public policies.