Changes in South American Hydroclimate under Projected Amazonian Deforestation.
Continued deforestation in the Amazon forest can alter the subsurface/surface and atmospheric branches of the hydrologic cycle. The sign and magnitude of these changes depend on the complex interactions between the water, energy and momentum budgets. To understand these changes, we use the Weather Research and Forecasting model with improved representation of groundwater dynamics and the added feature of water vapor tracers used to isolate the moisture that originates as Amazonian evapotranspiration. The control simulation uses temporally-varying MODIS-based observations of land use, and the deforestation simulations use a "business-as-usual" land-use scenario projected for 2040-2050. Our results show that deforestation leads to changes that are very different during the dry and wet seasons. During the dry season, replacing mature forest by crops results in increased albedo and in less available net radiation. This change, together with reduced leaf area of crops results in decreased evapotranspiration, less atmospheric moisture of Amazonian origin and an increase in temperature throughout the basin. However, we find no changes in precipitation. Conversely, during the wet season, the dominant mechanisms are related to changes in circulation. Surface winds increase significantly due to decreased surface roughness. Vapor transport increases throughout the deforested region and leads to an increase in easterly moisture export over Amazon, and significant decrease in precipitation within the deforested regions of eastern Amazon. Conversely, the precipitation increases over western Amazon and northern La Plata basins. Contrary to expectations, we find no evidence that precipitation changes are caused by reduced precipitation recycling, or by changes in the instability of the atmosphere.
