Effects of land-use changes on climate in southern South America

In the last decades, the agricultural areas over La Plata Basin and the Argentinean Pampas have been extended deforestation. With the aim of understanding the potential impacts of land-use changes over the South American climate, several simulations with the regional climate model MM5 were carried out for different idealized land-use scenarios representing agricultural expansion, reforestation and desertification, respectively. Results show a significant warming and drying when forests were replaced by bare soils due to an increase in the net radiation budget and a reduction in the latent heat flux. However, the replacement of forests by crops resulted in a decrease in the net radiation budget at the surface, together with a decrease in the latent and sensible heat fluxes, leading to a significant cooling over central and eastern Argentina and drying over Bolivia and western Paraguay. Finally, the shift from the actual land cover to crops produced a cooling and wetting mainly over northern Argentina, Paraguay and part of Bolivia due to a decrease in the net radiation budget and sensible heat flux and an increase in the latent heat flux. The regional response for these idealized scenarios exceeds the area where the land-use was changed, indicating that non-local mechanisms are important. A reduction in the roughness length when forest is replaced by either crops or bare soil leads to an increase in the northerly winds, which modifies the moisture flux convergence patterns and hence affects precipitation.