Resumen
Aim 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.Keywords: Annual water yield model; Separate evaluation method; North China.Abbreviations: AWY-Annual water yield model; AET-actual evapotranspiration; Y-annual water yield; P-precipitation; R-runoff; T-temperature.