ENSO Effects on the Shrubland-to-Cropland trend across the South American Diagonal, Central Argentina

Abstract

The Western or Sandy Pampa of Central Argentina lies on the ecotone between the xerohytic woodland (“espinal”) and the grassland praire. At the same time this region is subject to wet rainfall anomalies during ENSO years. This particular area, studied by images of different spatial and temporal resolution, is under a high agronomic pressure due to land-use changes from shrubland into cropland. This plain (covered by scattered transverse dunes inherited from the Wisconsinan Glaciation) is dominated by westerly winds with no topographic effects in the rainfall distribution. Precipitation increases to the east (Atlantic Ocean) from 400 to 900 mm/year. By the mean of composite Landsat TM images, the deforestation of the shrubland into crop fields was evaluated. This man-induced land-cover change could be followed comparing Landsat MSS images from the ’80 with TM images of 1998-1999. By the mean of Normalized Difference Vegetation indexes (NDVI) performed on NOAAimages from winter (July) and filtered by a mean kernel, it can be recognized the different patterns between “normal years” (1995,1999) and “ENSO years” (1998). In “normal years” the NDVI had low values while during “ENSO winters” the greenness was significantly higher. The wetlands “Bañados de La Amarga”, centripetal drainage basin of the Quinto river, is particularly sensitive to these interannual effects. These land-use changes are inducing unpredicted consequences in relation to soil conservation and alterations in the hydrological budgets.