Four decades of hydrological response to vegetation dynamics and anthropogenic factors in the Three-North Region of China and Mongolia

Afforestation has been initiated in Northeast Asia to improve ecological status. The responses of the regional hydrolog-ical cycle to vegetation restoration remain insufficiently explored. This study uses a variety of satellite-derived vegeta-tion variables and hydrological cycle components to scan the eco-hydrological regimes in the Three-North Region of China and Mongolia during the past four decades. We observe that vegetation productivity increases mainly in North China (NC), Northeast China (NEC), Northwest China (NWC), and the north of Inner Mongolia and Mongolia. Precipitation and runoff show a decreasing trend (-0.4 mm/year and - 0.6 mm/year, respectively), yet they are less correlated to the normalized difference vegetation index and leaf area index. Along with increasing vegetation pro-ductivity, evapotranspiration increases (0.05 mm/year) obviously in NC and NEC, while root soil moisture (-0.001 m3/m3/year) and terrestrial water storage (-2.0 mm/year) decrease in NC and parts of NEC and NWC. The correla-tion coefficient between evapotranspiration and vegetation variables is up to 0.73. Collectively, results imply one po-tential adverse response of terrestrial water fluxes to increasing vegetation. Independent ecological and hydrological datasets further corroborate our work. Climatic factors (i.e., downward shortwave radiation and air temperature) and human activities (i.e., aerosol optical depth, carbon dioxide, and water withdrawal) substantially affect regional hydrological cycles. Considering the increasing vegetation productivity in the Three-North Region of China and Mongolia is likely to continue in the 21st century based on the Sixth Coupled Model Intercomparison Project (CMIP6) simulations, the terrestrial water fluxes may undergo deficit pressure. Overall, this study comprehensively in-vestigates the vegetation and hydrology interplays, and provides a reference for protecting and improving ecological -hydrological conditions in Northeast Asia.