Abstract ID: 194

Impacts of Amazon land-cover change on the mean and interannual variability of the regional and global hydroclimate

It has recently been projected that agricultural expansion will eliminate 40% of Amazon forests during the next 50 years. Previous studies have suggested that such dramatic land-cover change can significantly alter regional and global hydroclimate. General circulation models (GCMs) and regional meteorological models have been used to assess such effects. However, both approaches have key limitations: the grid resolution of the GCMs is coarser than both the scale of actual land-cover change and topographical features such as the Andes, while mesoscale models typically obtain their requisite lateral boundary conditions from global simulations not accounting for land-cover change. In this study we illustrate how both problems can be simultaneously addressed using the Ocean-Land-Atmosphere Model (OLAM), a global Earth System Model employing a state-of-the-art grid structure which here enabled us to use an atmospheric resolution typical of a mesoscale model over South America while using a coarser resolution typical of other GCMs throughout the rest of the world. We first validated OLAM's ability to simulate the current-day mean and interannual variability (IAV) of precipitation in the Amazon by comparing model output to products from GPCP, CMAP, TRMM, and the NCEP/NCAR reanalysis. We found that resolving the Andes at resolutions < 100 km was essential in order for the model to reproduce the observed IAV. We then investigated how regional and global hydrological cycles were altered in OLAM when the model was forced with current projections of land cover change in Amazon basin. We found that, because of mesoscale feedbacks, the impact of land cover change on basin-wide Amazon precipitation was small relative to the previous projections of coarser-resolution modeling studies. However, changes in land-cover had important impacts on sub-basin scales with the eastern Amazon experiencing increased precipitation and the western Amazon experiencing decreased precipitation.

Session:  Feedbacks to Climate - Effects of deforestation on regional and global climate.

Presentation Type:  Oral