The agricultural expansion in South America’s Dry Chaco: Regional hydroclimate effects

Abstract. The Gran Chaco ecoregion is South America’s largest remaining continuous stretch of dry forest. It has experienced intensive deforestation, mainly in the western part known as Dry Chaco, resulting in the highest rate of dry forest loss globally between 2000 and 2012. The replacement of natural vegetation with other land uses modifies the surface’s biophysical properties, affecting heat and water fluxes and modifying the regional climate. This study examines land use and land cover changes (LULCCs) in Dry Chaco from 2001 to 2015, their effects on local and non-local climate, and explores the potential impacts of future agricultural expansion in the region. To this end, Weather Research and Forecasting (WRF) model simulations are performed for two scenarios: the first one evaluates the observed land cover changes between 2001 and 2015 that covered 8 % of the total area of Dry Chaco; the second scenario assumes an intensive agricultural expansion within the Dry Chaco. In both scenarios, deforestation processes lead to decreases in LAI, increases in albedo, and reductions in stomatal resistance, reducing the net surface radiation and, correspondingly, a decrease in turbulent fluxes suggesting a decline in available energy in the boundary layer. The result is an overall weakening of the water cycle in the Dry Chaco and, most prominently, implies a reduction in precipitation. A feedback loop develops since dry soil absorbs significantly less solar radiation than moist soil. Finally, the simulations suggest that the Dry Chaco would intensify its aridity, extending the drier and hotter conditions into the Humid Chaco.