Impacts Of Climate Change And Human Activitie On Vegetation NDVI In Loess Plateau

The Loess Plateau not only is the transition zone from semi-humid to semi-arid in China,but also is a key areas on the impact of the ecological environment construction and other human activities about vegetation changes.Based on MYD13Q1 data with spatial resolution of 250 m from 2001 to 2016,the meteorological data of 82 stations,the land use data and other statistical data on the Loess Plateau,using slope analysis,hurst index,partial correlation analysis,residual analysis and buffer analysis method,were used to analyze the dynamic changes of vegetation NDVI in the growing season,the effects and spatial variability of climate change and human activities on vegetation changes.Draw the following main conclusions:(1)The vegetation NDVI in the Loess Plateau from 2001 to 2016,in the interannual time,the NDVI changes of all seasons showed a significant increase(P <0.01),and there was a seasonal difference that summer and autumn was the highest and the lowest was spring in growth;the NDVI had decreased gradually from southeast to northwest on the spatial distribution;on the spatial variation trend,the slope of vegetation NDVI in the growing season was about 0.00578/16 a,showing an increasing tendency and a degenerating trend accounting for 40.83% and 25.05% of the study area respectively;in terms of vegetation continuity,the average Hurst average was 0.6569,and the areas of Hurst> 0.5 and Hurst <0.5 were respectively 54.71% and 14.38% of the total area,the positive continuity of vegetation change in the Loess Plateau is stronger than that in the reverse.(2)The temperature and precipitation of different vegetation areas in the Loess Plateau have shown that the trend of temperature rise is not large,and the rate of change is 0.0064/16 a,and the rate of precipitation change is forest>grassland>desert,the precipitation is generally the trend of fluctuation from rising to falling to rising;the correlation between vegetation NDVI and temperature is not high(-0.00249/16a),and temperature has little effect on the vegetation NDVI in different vegetation types;the vegetation NDVI had a significant response to precipitation(P<0.05)in desert area,and its spatial correlation was 0.0301/16 a,the precipitation was an important climatic factor for vegetation improve in grassland and desert areas,and the impact of forest area was not obvious.(3)In the background of conversion farmland to forest,the cultivated land had decreased by 10,939km2 in the Loess Plateau from 2001 to 2015,and is the largest land of decrease,and the rate of change was-5.07%,the proportion of the area showing improved trend are arable land,woodland and grassland as followed in the land use,and the proportions of degraded trend areas are construction land,unutilized land and water body in successively;there are positive and negative spatial differences in the impact of human activities on NDVI,and the area under the positive and negative disturbances respectively accounts for 62.12 % and 19.38%,the negative interferences are concentrated in the surrounding areas of some big cities;in typical cities about the trend of vegetation change in different rings,such as Xi'an and Taiyuan,the landscape pattern is the pattern of improve of urban center and degradation of peripheral areas,and expansion is an important factor about the decline of vegetation in the area around city,while the reasonable afforestation by human beings makes the vegetation in the urban center shows an improving trend.