Tropical forests make it rain: new understanding from observation and model-based approaches

Tropical forests play an important role in regulating climate and the hydrological cycle.  Rapid deforestation across the tropics is radically changing the land surface, causing local and regional warming and altering the pattern of precipitation. The biogeophysical mechanisms behind these changes are complex and still not fully understood: climate models disagree on the sign of the precipitation change in response to tropical deforestation and the extent to which recent tropical deforestation has altered precipitation remains highly uncertain. Here, we apply observation and model-based approaches to provide new information on how tropical deforestation impacts precipitation. We combine satellite-based precipitation and forest loss data to explore how tropical deforestation is associated with rainfall trends across the tropics (30°S–30°N) from 2001 to 2024. We find the largest precipitation declines within and downwind of regions that have experienced the largest reductions in tropical forest canopy cover. To explore mechanisms behind these observed precipitation changes, we analyse simulations from climate models participating in the Land Use Model Intercomparison Project (LUMIP). Models predict a diverging response of precipitation to Amazon deforestation, largely due to opposite moisture convergence responses across models. We find that models with larger positive surface albedo response to deforestation typically have larger reductions in evapotranspiration, moisture convergence and precipitation. Finally, we use simulations from the UKESM and the Brazilian Atmospheric Model (BAM) to simulate the local and regional climate responses to different future land use scenarios and explore potential impacts on human health, agriculture and fire.