Response of vegetation hydroclimatic stress indicators to global warming and deforestation in the Amazon rainforest

Abstract. The Amazon rainforest (ARF) plays a key role in regulating the global climate, sustaining exceptional biodiversity, and supporting the cultures of indigenous peoples and local communities. The ARF is also considered a tipping element, as deforestation and global warming may impose sufficient stress to trigger a transition to a tropical savanna state. However, the climate and vegetation responses to deforestation and global warming, as well as associated tipping thresholds, remain incompletely understood. Here, we examine the response of four hydroclimatic indicators to deforestation and warming and discuss their implications for forest stability. We performed four idealized ARF deforestation experiments with the Earth System Model MPI-ESM-HR at 2 °C of global warming. These scenarios were compared against two intact-forest scenarios for pre-industrial climate and for 2 °C warming. Our results show that deforestation of 25 % of the forest area can lead to 70 % being under significant hydroclimatic stress. The area under stress increases to 89 % when combining 25 % deforestation and 2 °C warming, exceeding the deforestation-only effects of 50 % deforestation (82 %). Mean Annual Precipitation (MAP) and Dry Season Length (DSL) show the strongest changes, but behave differently: MAP decreases strongly in and near newly deforested areas, while DSL increases across large forest regions downstream of the deforested areas. Although the rainforest remains stable in the model, the enhanced hydroclimatic stress would likely increase tree mortality in the real world if vegetation cannot adapt. Our results hence emphasize the risk of forest dieback at forcing levels that can be reached within the next few decades.