Isolating the Influence of Vegetation Variability of La Plata River Basin on the Climate of South America

The goal of our work is to isolate and quantify the local and remote biophysical influences of vegetation variability on the climate of South America through a combined observational and modeling study. The first part of this study uses remotely sensed land-surface characteristics alongside reanalysis data, and the stepwise generalized equilibrium feedback assessment (SGEFA) to isolate the effects of vegetation forcing on the atmosphere. The analysis uses a 34-year (1981-2014) record of the modified enhanced vegetation index (EVI2) from the NASA MEaSUREs Vegetation Index and Phenology dataset and the third-generation normalized difference vegetation index (NDVI3g) from the Global Inventory Modeling and Mapping Studies. The dominant pattern of variability, analyzed using empirical orthogonal function/principal component (EOF/PC) analysis on a basin-wide scale, is a vegetation dipole. Using SGEFA, we find that the dominant mode of vegetation variability over the La Plata River basin in austral Spring is linked with warmer temperature and enhanced precipitation over central and southern La Plata basin through modulation of the sub-basin scale patterns of surface heat fluxes (latent and sensible). We then use the Weather Research and Forecast (WRF) regional climate model with the added capability of water vapor tracers (WRF-WVT) to better understand the physical mechanisms linking the vegetation variability to atmospheric processes. WRF-WVT aids in the attribution of the atmospheric response to moisture recycling v/s thermodynamic/dynamic effects of the land surface for an improved understanding of land-atmosphere interactions over South America. This observed impact of vegetation on the seasonal accumulation of precipitation in the agricultural growing season is of crucial importance for the most heavily populated and economically active region of South America.