Hydrological impacts of land-use change and agricultural policy in the Brazilian Cerrado

Land-use change and climate variability are two of the most important forces driving changes to the surface water and energy balance in tropical ecosystems. Our analysis combines satellite-derived data on rainfall (CRU), evapotranspiration (MOD16), soil water storage (GRACE), and land cover (MOD12Q1) to understand the effect of past (2000-2012) land cover changes and climate variability on the water balance of the Brazilian Cerrado (savannah woodlands). Based on these historical relationships, we examine potential future land-use transitions from native Cerrado to pasturelands and mechanized agriculture, using the Brazilian Water Agency's (ANA) 12th order watersheds as our unit of analysis. In the Cerrado, these watersheds constitute nearly 37,500 units (mean area ~5,400 ha) and serve as a useful proxy for property-level land-use decisions. Our future scenarios evaluate the potential ramifications of recent changes in the Brazilian Forest Code, which we estimate may allow for legal deforestation of an additional 40 × 2 million hectares of native Cerrado. Our analysis indicates that historical land-cover changes have already caused a significant decrease in evapotranspiration, leading to a three-fold increase in discharge in small watersheds and a nearly 25% increase in large river basins like the Tocantins-Araguaia. As global demand for agricultural commodities continues to rise, it is likely that large-scale conversion of the Cerrado will continue or accelerate in the coming decade. Our research suggests that the cumulative impact of such large-scale land cover change may shift the water balance sufficiently to alter regional precipitation and deplete groundwater stores. Future research will focus on understanding the potential feedbacks of these large-scale hydrological changes on regional climate and agricultural productivity.