SUMMARY
To maintain the sustainable utilization of water resources and reduce soil erosion in the Loess Plateau, the Chinese government has adopted a number of environmental restoration strategies since 1999, including the Grain for Green Project (GFGP) and the Natural Forest Conservation Program; these large projects greatly alter the regional water cycle. Detecting runoff changes and quantitatively assessing the contribution of anthropogenic activities (including land use/cover change (LUCC) and water diversion) and climate change (including potential evaporation and precipitation) are imperative for implementing sustainable management strategies. Using observed records from 15 hydrological stations and 85 national meteorological stations from 1980 to 2013, the decomposition method, based on the Budyko hypothesis, is used to quantify the impact of climate variation and anthropogenic interference on annual runoff for the 12 catchments in the Loess Plateau. The results show the following: (1) the observed annual runoff exhibited a negative trend in all 12 catchments (significant in eight catchments) with a range of -1.94 to -0.16 mm·year-1 and exhibited a substantial difference before and after 1999; (2) the sensitivity of runoff to vegetation change, precipitation, and potential evapotranspiration increased in most catchments after 1999, indicating that great challenges and uncertainties might be introduced to regional water resource availability; and (3) the anthropogenic interference, particularly LUCC caused by forest strategies, has become the main contribution to runoff change. We suggest that more attention should be given to water resource availability and that the hydrologic consequences of revegetation should be taken into account in future management.