Variation and climate response of NDVI3g(1982—2013) in Binchang mining area of Shaanxi Province

In the past 30 years,the global normalized difference vegetation index (NDVI) showed an increasing trend, the start of the vegetation growing season (SOS) was advanced,the end of the growing season (EOS) was delayed and the length of growing season ( LOS) was prolonged. As the most intensive industrial and mining area of human eco- nomic activities,its ecological environment is one of the focal issues of environment and development. Under the back- ground of global climate change,the NDVI trend in the mining area and around can well reflect vegetation change in non-natural ecological zones and its response to global change at regional scale. Based on the long-term sequence of GIMMS AVHRR NDVI3g remote sensing images,the phenological information of vegetation cover was extracted by using IDL programming,linear regression and trend fitting in the study area from 1982 to 2013. Analyzing the month- ly,quarterly and annually variations of the mining area,buffer zone (10 km,20 km) and its calibration area,the varia- tion trends in SOS,EOS and LOS length were obtained,and finally the correlation between the climatic driving factors (i. e. precipitation,temperature) and the change of NDVI was analyzed combined with meteorological records. The temporal-correlation analysis demonstrates that the average annual NDVI of Binchang mining area increased slowly with an annual growth rate of 13. 31% over the past 32 years. But the total NDVI in natural ecological check area ( CK) showed apparent growth trend with an annual growth rate up to 19. 45% . Therefore,it can be concluded that the annual growth rate of NDVI in mining areas is significantly lower than that in the CK under the influence of human ac- tivities. Spatial-correlation analysis indicates that the original NDVI value of the Binchang mining area is higher than that of the CK. In the mining area,the vegetation SOS is 6±3 days ahead of time,the EOS lags behind 5±3 days and the LOS extends 11±3 days. The corresponding values in the CK area are 3±3 days,3±3 days and 6±3 days,respec- tively. The extension of LOS in the mining area is longer than that in CK for 6 days. Climate-correlation analysis shows that Binchang mining area is located in the semi-humid climate zone. As a result,the response of vegetation to temper- ature change is higher than to precipitation,and vegetation growth has a lag of 2 to 3 years in response to precipitation. In other word,the increase of NDVI depends on the interactions of temperature rise and precipitation decrease. The study concludes that the mining activities slow down the vegetation growth in the mining area and around,and the an- nual growth rate of NDVI is obviously lower than that in the CK. Under the effects of global change and based on the extension of LOS,the vegetation LOS extends further in the mining area due to the human activities.