Spatiotemporal NDVI Variations And Driving Factors In Hexi Corridor And Its Surrounding Area

Vegetation cover is a commonly used indicator to evaluate terrestrial environmental conditions and to disclose environment evolution and transition.Spatiotemporal variations of Hexi Corridor and its surrounding area vegetation cover during 2000-2010 have been investigated using MODIS NDVI data and the cause of vegetation cover changes have been analyzed,considering the climate changes and human activities.The vegetation cover of the study area increased from2000 to 2010.The greenness of vegetation showed a significantly increasing trend from the northwest to the southeast,which was similar to the spatial distribution of the annual precipitation.Vegetation variations have a close relationship with precipitation variations in Qilian Mountains region,but NDVI negatively correlated with the precipitation in the oasis area.Temperature is an important factor to control the seasonal growth of vegetation.On the one hand the increasing temperature increased the drought of soil and inhibited the growth of vegetation in the Wuwei oasis and Wushao Mountains in summer;on the other hand the increasing temperature can also respectively advance and prolong the growing periods in oases and the most areas of Qilian Mountains in spring and autumn.The NDVI showed slight degradation in March,July and September which mainly distributed in the Qilian Mountains and Wuwei oasis,especially in Wushao Mountains.In March,owing to low temperature,reaction rate of vegetation was too slow to benefit the growth of plants in Qilian Mountains where the elevation is high.In July,the physiological activities of the plants decreased because of the high temperature and decreasing precipitation,which led to vegetation degradation.In September,the reducing temperature enhanced the intensity of transpiration,and the decreasing precipitation reduced the available moisture for plants,so that the vegetation showed slight degradation in Qilian Mountains.In May,August and October,the NDVI was manifested in a significant improvement,which mainly distributed in the artificial oases and Qilian Mountains.Abundant precipitation provided the necessary water for plant growth and suitable temperature increased the efficiency of photosynthesis,so the vegetation was significantly improved in Qilian Mountains.And the implementation of large-scale vegetation construction has also led to some beneficial effect in shelterbelts around artificial oases and grassland of Qilian Mountains.The improvement ofproduction technology,especially the improving irrigation,which is beneficial to growth of vegetation in the oasis.In this study,climatic factors and human activities were used to monitor the vegetation cover in Hexi Corridor and its surrounding area,which in order to analyze the different effects of natural factors and human activities on vegetation cover change.It provided scientific basis for the restoration of vegetation and management fragile ecological environment in study areas.At the same time,it can provide theoretical value and practical guiding significance for the social,economic and sustainable development of the region.