Large-scale afforestation significantly increases permanent surface water in China's vegetation restoration regions

China is facing the challenge of the uncertain impacts of large-scale afforestation on regional water resources. However, the effects of vegetation cover changes on the variation in surface water at the regional scale are still controversial. Here, we focused on the 0.9 million km2 vegetation restoration region in China, where the highest significant vegetation cover changes on the earth. Multi-source remote sensing data were used to describe the characteristics of seasonality and transition of surface water and to analyse the causes of surface water changes from climate, vegetation cover and other human factors. Our results show that the annual maximum NDVI of Northeast region (NE) and Loess Plateau region (LP) increased significantly from 0.74 to 0.85 and 0.49 to 0.62 from 2000 to 2015, respectively. Meanwhile, permanent water, as a vital component of surface water, exhibited net increases of 695.6 km2 and 119.4 km2 in NE and LP from 2000 to 2015, respectively. The extension in permanent water and the implementation of ecological projects exhibited highly consistent spatiotemporal patterns. Statistical analysis indicated that vegetation cover is an important factor in controlling permanent water changes. Human activities such as building dams and reservoirs are also an important explanatory variable for permanent water increases. The newly built dams contributed 43% in NE and 25% in LP to the increase in permanent water. In addition, although climatic factors were not the main factor influencing permanent water, precipitation significantly affected the total surface water in NE. These findings have potential implications for understanding surface water and forest dynamics and formulating regional development plans in the vegetation restoration region in China.