Hydrological Consequences of Deforestation and Forest Degradation in the Amazon Agricultural Frontier

Abstract:

Deforestation in the tropics causes important changes in the energy and water balance because pasturelands and croplands generally have a higher albedo and decreased water demand, evapotranspiration, and atmospheric turbulence compared to the forests they replace. These changes to the water and energy balance work at a variety of time and space scales and the combined influences on regional hydrology are complex. Field observations, satellite data products and a suite of numerical ecosystem models have been used to document and understand changes to the energy and water balances at micro (<1 km²), meso (100s km²) and large (10,000 km²) spatial scales in the southeastern Amazon. The results show that at regional scales deforestation has decreased net radiation and evapotranspiration and increased surface temperature, sensible heat flux, soil moisture, stream flow and stream temperature. These changes result from the increased albedo, reduced leaf area index, altered phenology, decreased root density and depth, and total water demand of the pasture and crops compared to the native vegetation. Global and meso-scale climate model applications indicate that continued deforestation may significantly reduce regional precipitation because of decreases in the net surface radiation, surface roughness, moisture convergence over the basin, and water recycling. Future changes brought about by deforestation may be of a scale to negatively impact ecosystem services such as hydropower generation and crop productivity.