Spatial-temporal changes in vegetation cover in a typical semi-humid and semi-arid region in China: Changing patterns, causes and implications

As a principal part of terrestrial ecological environment, vegetation is dominant in maintaining the function of terrestrial ecosystem. In order to systematically study the change patterns, causes, and implications of vegetation cover in a typical semi-humid and semi-arid region under changing environments, the Wei River Basin (WRB) was selected as the case study. Spatial-temporal changing patterns of vegetation cover in the WRB were firstly examined based on satellite-based Normalized Difference Vegetation Index (NDVI). Then, the underlying causes were studied by investigating the relationships among precipitation, temperature and soil moisture (SM) condition using the cross wavelet technique. Furthermore, implications of changing vegetation cover on runoff and sediment load were also analyzed. Results indicated that: (1) significant increasing trends of vegetation cover were detected at annual scale; and seasonal vegetation cover in the WRB is characterized with significant increasing trends in spring and autumn, while insignificant decreasing trend of summer vegetation cover in the upstream and midstream; (2) stationarity of annual NDVI is invalid with change points identified in all subregions of the WRB; (3) the correlations between annual NDVI series and precipitation, temperature and SM series demonstrate that significant increasing vegetation cover in the WRB are more influenced by temperature and SM condition than precipitation, anthropogenic factor however is also another reason for changing vegetation cover in the basin; and (4) statistically significant negative correlations between NDVI and runoff, sediment discharge imply that aside from human activities, increasing vegetation cover partially contributes to the reduction of runoff and sediment in the WRB. These findings are helpful for scientific assessment of ecological restoration projects, thereby facilitating local soil and water conservation.