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 (WRF) model with improved representation of groundwater dynamics and the added feature of Amazonian moisture tracers. The control simulation uses moderate resolution imaging spectroradiometer (MODIS) based observations of land use, and the deforestation simulations use a "business-as-usual" scenario projected for 2040-2050. Our results show that deforestation leads to changes that are seasonally very different. During the dry season, deforestation results in increased albedo and less available net radiation. This change, together with reduced leaf area, results in decreased evapotranspiration (ET), less atmospheric moisture of Amazonian origin, and an increase in temperature. However, we find no changes in precipitation over the basin. Conversely, during the wet season, 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, and significant decrease in precipitation within the deforested regions of Eastern Amazon. Contrary to expectations, the moisture tracers in WRF show no evidence that precipitation decreases are due to recycling or changes in stability.