Recent trends in vegetation dynamics in the South America and their relationship to rainfall

This research investigates spatial patterns of Normalized Difference Vegetation Index (NDVI) and rainfall variability in South America and their relationships based on analyses of the Standardized Difference Vegetation Index (SDVI) and the Standardized Precipitation Index (SPI) for the period April 1998-March 2012. The time series of SPOT-Vegetation 10-daily composite NDVI data at 1-km resolution was smoothed and subsequently synthesized to monthly images using the maximum value composite technique. Furthermore, 10-daily rainfall estimates at 0.25A degrees resolution, available from the European Centre for Medium-Range Weather Forecasts through MeteoConsult and the Monitoring Agricultural ResourceS unit, were combined to retrieve monthly composites. In order to assess spatial patterns and rates of change, linear least squares trend analyses were performed on the SDVI time series and the SPI time series, taking into account the accumulated rainfall over the respective best lag. Only trends with Pearson's correlation coefficients significantly different from zero (p < 0.05) were considered significant. The results indicated that vegetation degradation is coupled to a significant decrease in the amount of rainfall in the last 14 years in 8 % of South America's area. In contrast, in 18 % of the subcontinental area, vegetation greenness has significantly increased over the last 14 years, coupled to an increase in rainfall. For 46 % of the study area, significant degradation or greening processes could not be linked to changes in rainfall over time, indicating human impact or the influence of other climatic factors, such as temperature and net radiation.