Impacts of Land Use Change in Southern South American Climate

N. L. PESSACG; S. A. SOLMAN

Foz de Iguazu

Congreso; The Meeting of the Americas AGU; 2010

American Geophysical Union

La Plata Basin (LPB) and the Argentinean Pampas are two of the most important agricultural regions in the world. In the last decades the areas devoted to agriculture production over the La Plata basin region have been extended at the expense of deforestation and replacement of natural pastures. These changes in land use and land cover may modify the exchanges of energy and moisture between the land surface and the atmosphere, through changes in albedo, aerodynamic roughness and root depth, resulting in local and regional changes in climate over the region. With the aim of analyzing and understanding how these changes may affect the regional climate, sensitivity experiments to land use/land cover change were performed with the Fifth-generation Pennsylvania-State University-NCAR nonhydrostatic Mesoscale Model (MM5). Based on observational evidences of land use changes over South America, an idealized land use scenario was defined, in which the natural land cover was replaced by dry land crop pasture. The regions where land cover was modified are shown in Figure 1. This highly idealized scenario has the purpose of evaluating what extent large changes in land use may impact on the climatic characteristics over the target region. Ensembles of one-year length experiments for the land use change scenario and control simulations were compared. The period simulated corresponds to 1989-1990 and the focus is on DJF, the austral summer season. The changes in land cover over the northern part of the La Plata Basin, where croplands replace evergreen broadleaf and savannah, induced two feedbacks. On one hand, an increase of albedo leads to a reduction of the surface temperature and the sensible heat flux. On the other hand, a decrease of roughness drives to a reduction of latent heat flux associated with a decrease of the capacity of root for extracting soil moisture, mainly over northeastern Argentina. The soil moisture showed large decreases within the upper levels of the soil and the deeper layers of the soil experienced an increase in soil moisture, probably due to the reduced root length. The reduced availability of moisture near the surface together with a relatively more stable planetary boundary layer resulted in a decrease of low-level cloud cover and a decrease in precipitation, mainly due to a decrease in the intensity of heavy precipitation events. In contrast, the southern part of the basin presents the opposite conduct, as croplands replaces shurbland, a decrease in albedo and a weak increase in surface temperature is apparent. However, no significant changes in precipitation are evident.