Temporal and spatial variations of NDVI and its driving factors in the Yanghe Watershed of northern China

ObjectiveThe study of vegetation cover change and driving factors in the Yanghe Watershed of northern China can provide important reference value for regional ecological construction and vegetation restoration.

MethodBased on SPOT Vegetation NDVI data, meteorological data and land use data, the impacts of climate change and human activities on vegetation NDVI in the Yanghe Watershed during 1999 to 2015 were explored using trend analysis, partial correlation analysis, multiple correlation analysis and residual analysis.

Result(1) The vegetation NDVI of the Yanghe Watershed in the last 17 years generally showed an upward trend with the growth rate of 3.9% every 10 years. The area proportion of increasing and decreasing NDVI were 57.90% and 1.13%, respectively. Shrub land and forest improved significantly. (2) In the study area, 51.99% of the regional NDVI changes were driven by climate factors, with area driven by precipitation and both precipitation and temperature accounted for 26.13% and 25.44% of the total area of the watershed, respectively. The former area was mainly distributed in Xinghe, Shangyi, Yanggao, Tianzhen, Huaian and Xuanhua regions, and the latter was distributed in the south of Xinghe and a banded region extending to the southeast. Furthermore, annual mean temperature had little effect on the change of NDVI. (3) The interference of human activities to the vegetation of Yanghe Watershed had an increasing trend since 1999, with more positive impacts and the growth rate of 4.5% every 10 years. The positive effects of human activities on vegetation were mainly distributed in Shangyi, Wanquan, Chongli and Yanggao regions, while the negative effects mainly generated from towns and countries with dense population.

ConclusionThe change of NDVI in the Yanghe Watershed during the year of 1999-2015 was the result of combined effects of climate change and human activities, while human activities had the bigger effect. Beijing-Tianjin Dust Storm Source Control Project and other ecological projects play an important role in the improvement of NDVI in Yanghe Watershed of northern China.