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Abstract:
Recent publications indicate that the Amazon may be acting more as a carbon source than a sink in some regions. Moreover, the Amazon is a source of moisture for other regions in the continent, and deforestation over the years may be reducing this function. In this work, we analyze the impacts of elevated CO2 (eCO2) and Land Use Change (LUC) on Gross Primary Productivity (GPP) and evaporation in the Southern Amazon (70S 140S, 660W 510W), which suffered strong anthropogenic influence in the period of 1981‒2010. We ran four Dynamic Global Vegetation Models (DGVMs), isolating historical CO2, constant CO2, LUC, and Potential Natural Vegetation (PNV) scenarios with three climate variable datasets: precipitation, temperature and shortwave radiation. We compared the outputs to five “observational” datasets obtained through eddy covariance, remote sensing, meteorological measurements, and machine learning. The results indicate that eCO2 may have offset deforestation, with GPP increasing by ∼13.5% and 9.3% (dry and rainy seasons, respectively). After isolating the LUC effect, a reduction in evaporation of ∼4% and ∼1.2% (dry and rainy seasons, respectively) was observed. The analysis of forcings in subregions under strong anthropogenic impact revealed a reduction in precipitation of ∼15 and 30 mm, and a temperature rise of 10 and 0.60 C (dry and rainy seasons, respectively). Differences in the implementation of plant physiology and Leaf area Index (LAI) in the DGVMs introduced some uncertainties in the interpretation of the results. Nevertheless, we consider that it was an important exercise given the relevance.
