The rough reality: How forests reshape tropical circulation and hydroclimate

While afforestation and avoided deforestation are important strategies for climate change adaptation and mitigation, their effects on atmospheric circulation and hydroclimate remain underexplored. Here, we use future afforestation simulations in an SSP1-2.6 and SSP3-7.0 world from seven CMIP6 models from the Land Use Model Intercomparison Project (LUMIP). Our results reveal robust increases in precipitation and evapotranspiration, coupled with widespread decreases in net moisture flux (i.e., decreases in precipitation minus evaporation) in the tropics, particularly over Africa. The moisture flux changes are driven by opposing effects of afforestation on upper and lower-tropospheric circulation: The increase in surface roughness significantly slows down the moisture-laden surface winds from the ocean, reducing moisture transport and suppressing topographically-induced precipitation. However, the concurrent increase in near-surface moist static energy strengthens convection and thus the upper-tropospheric circulation. These findings underscore the significant role of surface roughness changes and land-atmosphere interactions in shaping tropical hydroclimate, and highlight the need for careful consideration of the hydroclimate impacts of land-based climate strategies.