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

Reducing uncertainty in future projections of rainforest precipitation is a major challenge in adapting to climate change and preserving the Earth's biodiversity. Here, we investigate how rising CO₂ effects on plant physiology impact precipitation in three main rainforests. We show that their differences lie in how land-surface warming interacts with their climatological atmospheric circulation, regardless of their reliance on evapotranspiration. 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 climatological circulation pattern leads to a precipitation-change dipole, with reduced rainfall in central and eastern Amazonia and increased rainfall in the west. The opposite dipole emerges when the land-surface does not warm, so that rainfall over eastern Amazonia increases as a direct response to reduced evapotranspiration. This improved understanding points the way to reducing uncertainty through targeted improvements to climate models and by searching for emergent constraints on atmospheric circulation patterns.