Objective  Significant restoration of vegetation in arid area can affect underlying surface conditions of the basin and change the hydrological process, which in turn affects the sustainable use of water resources in the basin. Assessing the spatial and temporal variation pattern of vegetation and clarifying its contribution to the runoff change is the premise of water resources management. This will also be helpful for evaluating the implementation effect of the vegetation restoration project.

  Method  Taking the typical semi-arid area of vegetation restoration, Kuyehe River Basin of northern China as the study area, based on the normalized difference vegetation index (NDVI), hydrological and meteorological data, this paper analyzes the impact of vegetation changes on runoff change during 1982−2015 based on the Budyko hypothesis of the Fu’s model.

  Result  (1) The break point of observed runoff occurred around year 1998, and the changing rates of runoff and human water consumption reached −55.5% and 92.3%, respectively before and after the break point, with a significant difference (P < 0.05); while the precipitation and dryness index increased by 2.6% and 1.9%, respectively, without significant difference (P > 0.05). (2) The basin NDVI was significantly different before and after the break point. Approximately 88.7% of basin area showed a significant increase trend (P < 0.001), especially in the downstream, indicating that the vegetation was greatly restored. The optimal solution of the watershed parameter was 2.37, and the fitted parameter and constant term were 20.407 and −1.868, respectively (P < 0.05), demonstrating that the fitting effect was good, and the applicability was strong. (3) The contribution rate of vegetation change to runoff reached 84.9%, while the contribution rates of climate change and human activity impact to runoff were 9.3% and 5.8%, respectively.

  Conclusion  It shows that the vegetation in the basin has been greatly restored; the greening of vegetation becomes the dominant factor determining the change of runoff, followed by climate change and human activities. The long-term ecological hydrological effects of vegetation changes need to be further investigated. The results of this study can provide a reference for the implementation of ecological restoration projects and decision-making.