Latitudinal divergence in runoff responses to global forestation due to forest-atmosphere feedbacks

Forestation is a pivotal nature-based solution for mitigating global warming, yet its unintended hydrological outcomes and associated geospatial patterns remain understudied. Here, we combine land-atmosphere coupled models with the Budyko framework to show that forest-atmosphere feedbacks dominate a latitudinal divergence in runoff responses induced by global potential forestation, with increases in tropical regions but declines in boreal regions. In tropical regions, substantial precipitation gains due to intensified upward moisture transport overwhelm the negative effects of forest-driven evapotranspiration (ET) enhancement. Conversely, in boreal regions, limited precipitation gains are insufficient to offset enhanced evaporative loss, driven by increased atmospheric demand due to elevated surface net radiation. The negative effects of direct forest expansion vary along the dryness gradient, with peak impacts in energy-water transitional regions. Our study highlights the necessity to incorporate hydrological considerations into carbon- or temperature-focused afforestation planning, and caution afforestation at high-latitudes where new forests may exacerbate water scarcity.