Divergent Hydrological Responses to Forest Expansion in Dry and Wet Basins of China: Implications for Future Afforestation Planning
Afforestation to control soil erosion has been implemented throughout China over the past few decades. The long-term hydrological effects, such as total water yield and baseflow, of this large-scale anthropogenic activity remain unclear. Using six decades of hydrologic observations and remote sensing data, we explore the hydrological responses to forest expansion in four basins with contrasting climates across China. No significant change in runoff was found for the period 1970–2012 for the cold and dry Hailar River Basin in northeastern China. However, both forest expansion and reduced precipitation contributed to the runoff reduction after afforestation since the late 1990s. Similarly, afforestation and drying climate since the mid-1990s induced a significant decrease in runoff for the Weihe River Basin in semi-arid northwestern China. In contrast, the two wet basins in the humid southern China, Ganjiang River Basin and Dongjiang River Basin, showed insignificant changes in total runoff during their study periods. However, the baseflow in the winter dry seasons in these two watersheds significantly increased since the 1950s. Our results highlight the longterm variable effects of forest expansion and local climatic variability on basin hydrology in different climatic regions. This study suggests that landuse change in the humid study watersheds did not cause dramatic change in river flow and that region-specific afforestation policy should be considered to deal with forestation-water quantity trade-off. Conclusions from this study can help improve decision-making for ecological restoration policies and water resource management in China and other countries where intensive afforestation efforts are taking place.