Impacts of Deforestation on Long-term Trends of Precipitation, Evapotranspiration and Soil Moisture in the Amazon River basin

Abstract:

Long-term trends in monthly series of precipitation and soil moisture are quantified in deforested sub-catchments of the Amazon River basin, during the 2001-2016 period. For estimation purposes, we use Empirical Mode Decomposition to filter out all climate variability modes of time series with the aim of extracting the residual of the series, which captures the long-term trend. Monthly precipitation data comes from TRMM, actual evapotranspiration from TerraClimate, and soil moisture from TerraClimate, for 38 basins with a percentage of forest loss forest up to 19.6% accumulated for the study period, as seen by the Global Forest Watch. Besides, we use the Mann-Kendall test for autocorrelated data to assess the statistical significance of the trends found. Analysis of precipitation series shows decreasing trends (57.89%, between 5.85-0.44 (mm month^-1) yr^-1) and increasing trends (34.%, 0.14-4.54 (mm month^-1) yr^-1); however, the magnitude of decreasing trends is largest located in deforested areas over southeastern Amazonia and the Colombian Amazon. Actual evapotranspiration shows increasing trends in 51.3% of river basins, between 0.01-0.82 (mm month^-1) yr^-1, and decreasing trends in 38.5% of river basins, between 1.40-0.02 (mm month^-1) yr^-1. Soil moisture exhibits decreasing trends in 60.53% of river basins, between 1.87-0.01 (mm month^-1) yr^-1 for the 15-year period. Overall, our results provide more evidence of the hydrological impacts of deforestation in the Amazon River basin, in particular about the drying out of the atmosphere over southeastern Amazonia as a result of human activities (Barkhordarian et al., 2019), in association with the identified decreasing trends in precipitation and soil moisture at sub-catchment scales, as shown in Figure 1.