Surface Warming and Atmospheric Circulation Dominate Rainfall Changes Over Tropical Rainforests Under Global Warming

This study investigates how the direct effects of CO2 quadrupling on plant physiology impact precipitation in three main rainforests. We show that differences between the regions lie in how land‐surface warming (driven by reduced transpiration) interacts with their climatological atmospheric circulations, regardless of their reliance on evapotranspiration. Various atmosphere‐only experiments from two General Circulation Models are used. We find that over New Guinea, land‐surface warming amplifies moisture convergence from the ocean and increases rainfall. In the Congo, no clear rainfall changes emerge as the land‐surface warming effect is offset by migrations of rainfall. In Amazonia, the interaction of land‐surface warming with the climatological circulation pattern leads to a precipitation‐change dipole, with reduced rainfall in central and eastern Amazonia and increased rainfall in the west. Plain Language Summary Predicting how tropical rainforests will be influenced by climate change is crucial and remains a challenge. We show that precipitation changes over rainforests are predominantly driven by land‐surface warming, caused by reduced transpiration from plants and its interaction with the atmospheric circulation in each region, which explains why each rainforest responds differently. These results rely on model experiments that decompose the complex effects of vegetation changes caused by rising CO2. This study points towards two main ways of reducing uncertainties in future projections: 1) by improving the models' representation of tropical circulation and vegetation and 2) by searching for emergent constraints on rainforest atmospheric circulation and the impact of vegetation changes. Key Points The three major rainforests respond differently to CO2‐induced plant physiology changes These differences lie in how the related land‐surface warming interacts with the circulation They are not driven by differences in evapotranspiration and recycling rate