Impact of deforestation on global monsoon precipitation   

The global monsoon system represents the dominant variation in the climate with profound regional and global impacts, influencing the livelihood of billions of people. However, how large-scale deforestation induced changes in water cycle and energy balance may modify global monsoon systems are not well understood. In this study, we investigate the biophysical effect of deforestation on global monsoon precipitation and circulation based on multiple earth system models in the Land Use Model Intercomparison Project (LUMIP). The results show that large-scale deforestation induces global monsoon precipitation and circulation intensity weakening. A 20 million km2 of global tree cover loss leads to annual precipitation reduction of about 15.0 mm per year (mm yr-1) and 26.2 mm yr-1of Multi-Model Ensemble (MME) in global monsoon and land monsoon domain. The precipitation is reduced by 16.8 mm in the Northern Hemisphere summer monsoon (NHSM) regions from May to September with weakened circulation intensity. Deforestation induces temperature asymmetry between the northern hemisphere and the southern hemisphere, and hemispheric thermal contrast is thus decreased. As a result, the north-to-south meridional pressure gradient weakens, leading to the NHSM circulation and precipitation intensity decrease. Deforestation-induced hemispheric temperature asymmetry also increases the northward cross-equatorial atmosphere heat transport that drives southward shift of Intertropical Convergence Zone, which suppresses the NHSM precipitation. The drying monsoon region in response to deforestation is fairly consistent among the models implying the adverse effects of large-scale deforestation beyond the region of land use change.