RESEARCH ARTICLE OPEN ACCESSforest project, Desertification control program and the wind breaker belt project in the north, have been implemented in the past few decades (Li, 2004). Over the past 20 years in particular, comprehensive control of soil erosion has brought noticeable improvements, and soil erosion in North China has been effectively controlled by afforestation and construction of water conservancy projects (Wei et al., 2005).While the natural eco-environment of North China improves effectively, the water yield from the mountain areas, which are essential sources of freshwater supply for urban people, AbstractAim of study: We studied effects of climatic variability and afforestation on water yield to make a quantitative assessment of the hydrological effects of afforestation on basin water yield in the Rocky Mountain Area of North China.Area of study: Seven typical forest sub-watersheds in Chaobai River watershed, located near Beijing's Miyun Reservoir, were selected as our study object.Material and methods: Annual water yield model and Separate evaluation method were applied to quantify the respective contributions of changes in climate and different vegetation types on variations in runoff.Main results: Statistical analysis indicated precipitation did not vary significantly whereas the annual runoff decreased significantly in the past decades. Although forest increased significantly in the late 20th century, climatic variations have the strongest contribution to the reductions in runoff, with the average contribution reaching 63.24%, while the remainder caused by human activities. Afforestation has a more positive impact on the reduction in runoff, with a contribution of 65.5%, which was more than the grassland of 17.6% and the farmland of 16.9%.Research highlights: Compared to the impact of climatic change, we believe the large-scale afforestation may not be the main reason for the reductions in basin water yield.

The hydrological information derived from a digital elevation model is very important in distributed hydrological modeling. As part of alpine hydrological research on stream network modeling using remote sensing data in the northeast of the Tibetan Plateau, three digital elevation model (DEM) datasets were obtained for the purpose of hydrological features, mainly including channel network, watershed extent and terrain character. The data sources include the airborne light detection and ranging (LiDAR) with point spacing of 1 m, the High Mountain Asia (HMA) DEM and the Shuttle Radar Topography Mission (SRTM) DEM. Mapping of the watershed and stream network was conducted using each of the three DEM datasets. The modeled stream networks using the different DEMs were verified against the actual network mapped in the field. The results show that the stream network derived from the LiDAR DEM was the most accurate representation of the network mapped in the field. The SRTM DEM overestimated the basin hypsometry relative to the LiDAR watershed at the lowest elevation, while the HMA DEM underestimated the basin hypsometry relative to the LiDAR watershed at the highest elevation. This may be because, compared with the SRTM DEM and the HMA DEM, the LiDAR DEM has higher initial point density, accuracy and resolution. It can be seen that the LiDAR data have great potential for the application in hydrologic modeling and water resource management in small alpine catchments.