ENSO-driven climatic and vegetation changes in Amazonia by the end of the century

Abstract

Climate change and large-scale deforestation in the Amazon could lead to biome state change from rainforest to savanna. Model simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5) provided little to no evidence for localized dieback events. In contrast, simulations from the next phase (CMIP6), featuring the new generation of models that sometimes include interactive vegetation carbon and forest fires, suggested the occurrence of a dieback in certain regions. El Niño-Southern oscillation (ENSO) substantially affects year-to-year variations in temperature and precipitation in the Amazon. The El Niño phase is associated with much higher temperatures, considerable rainfall deficits and elevated risks of forest fires. Here we investigate future climate and vegetation changes in Amazonia driven by ENSO using the CMIP6 model simulations. Our results suggest that in addition to the northeastern part that was most affected during the historical period (between 1980 and 2000), the southwestern region will become highly vulnerable to temperature and precipitation impacts linked to ENSO in the future. This is a consequence of much higher temperatures of up to 9 °C, and decreased precipitation of up to 120 mm/month projected to occur in association with El Niño by the end of the century. Some of the highest tree fraction reductions are expected over this newly vulnerable region—up to 15% according to the CMIP6 model ensemble, and up to 26% according to dynamic vegetation models alone, with implications for local regime shifts from forest to non-forest states.