| As natural resource, land is the basic production materials and survival environment, and is also the base of life in ecosystem. Land degradation is a significant decline process of land productive capacity and land use value influenced by natural factors and human activities. Desertification, biodiversity degradation and soil erosion have become increasingly common and serious, which could destroy the dynamic balance of matter and energy of natural ecological system, and threat the food safety and human health. All of these hampered the sustainable development of economy and society. It is the urgent need and to be solved problem to explore the driving mechanism of land degradation under the background of climate change, which contribute to the harmonious development of nature and human society. The arid region characterized fragile ecosystem is extremely sensitive to climate change, climate variation and irrational human activities can easily cause serious land degradation. The New Silk Road Economic Belt is mainly located in the inland arid area in Asia, the serious soil erosion and land desertification are not conducive to the regional economic cooperation and sustainable development. It is necessary for monitoring and evaluating the present situation of land degradation, which has the theoretical significance for ecosystem restoration, regional economic cooperation and progress of the New Silk Road Economic Belt of Asia.Based on GIMMS3 g NDVI and MODIS NDVI remote sensing data, combining with the high spatial resolution climatological data, the objiective of this study was to asses the land degradation, explore the driving mechanism and analyze the effect of human activity on regional land degradation quantitatively using the linear fitting, multivariate regression and residual analysis. The main purpose is to provide a scientific basis for prevention and control in land degradation in the Silk Road Economic Belt of Asia. The main results were as follows:(1) The upward trends in temperature and potential evapotranspiration were significant, and upward trend in precipitation was not significant, the variation in Palmer drought index and Standardized precipitation evapotranspiration index showed the study area were experiencing the drier and drier climate. The temperature in Mediterranean Forests Woodlands and Scrub, Deserts and Xeric Shrublands increased faster, variations in precipitation of Tropical and Subtropical in low latitudes were larger. The increase in potential evapotranspiration and decrease in drought index increase regional drought degree.(2) The high value of NDVI located in the northeast of China、India peninsula and Turkey showed good vegetation, the low value of NDVI distributed in eastern of Inner Mongolia of China、southern part of Tibet Plateau、western part of Central Asia and Arabian peninsula showed bad vegetation. The percentage of increasing trend in annual NDVI was 63.76% during 1982-2013, which mainly located in the most parts of Turkey and India peninsula. NDVI in study area experienced a upward trend, followed downward trend and then upward trend. The magnitude of increase of NDVI in Mediterranean Forests Woodlands and Scrub is largest with the slope of 0.18/100 a, Equatorial tropical grassland increased larger with the slope of 0.14/100 a in different climate zones.(3) The correaltaion between annual NDVI and temperature, precipitation showed positive relationship in most region, with the percentage of 69.64% and 74.50%, respectively. The NDVI correlated to precipitation significantly in the northern part and southern part of central Asia, western part of India and eastern part of Mongolia plateau. As for evapotranspiration, their correlation indicated negative relationship, in which significantly negative corraltion concentrate on Central Asia, the northern part of India peninsula、Mongolia and Inner Mongolia in China. The average correlation coefficient was 0.19 between NDVI and drought index, up to 41.47% showd significantly positive, distributed in central Asia、India、Mongolia plateau and the western part of Turkey. The partial correlation coefficient between NDVI and drought index is highest. The NDVI negatively correlated with temperature and standardized precipitation evaporation index, positively correlated with precipitation and potential evapotranspiration.(4) In the Silk Road Economic Belt of Asia, the high index of land degradation distributed in India peninsula、the northern part of Turkey and the northeastern part of China showed better vegetation, low index of land degradation distributed northwestern part of China、the western part of central Asia and Arabian peninsula showed bad vegetation. The percentage of significant land degradation and more significant land degradation is 53.29% and 32.66%, respectively, in whole study area. The positive effect from human activities on vegetation varation loacated in India in South Asia, central part of central Asia and Turkey, the negative effect concentrated on the northern part of central Asia. The index of land degradation in tropical and subtropical is higher, which showed a lower land degradation degree. The index of land degradation in Montane Grasslands、Shrublands and Desert is lower, which showed a higher land degradation degree. Land degradation dynamic index suggested that human activities mainly made positive effect on regional vegetation changes and affected vegetation changes significantly in Montane Grasslands and Shrublands.(5) The regression equation to simulate the relationship between climate and vegetation showed that human activities had an negative effect on regional vegetation in 80 s and changed to positive effect in 90 s. The NDVI residual in tropical forests、grasslands and scrub increased significantly, in which human activities contributed to vegetation growth. The NDVI residual in Flooded Grasslands and Savannas decreased significantly, in which human activities made negative effect on vegetation. The NDVI residual in boreal climates and Tundra climates indicated decline trends, the other climate zone showed increasing trends, with significant upward trends in Equatorial tropical grassland and Savanna climates, which suggested human activities influenced strongly on the regional vegetation growth.(6) Based on MODIS NDVI data, the spataial distribution of annual NDVI and NPP showed high values in the southeast and low values in the northwest of China. The upward trend of annual NDVI and NPP was significant, with the slopes of 0.07/100 a and 148gC/m2/100a2. Human activities promoted vegetation increase in northeat of China and southern part of Shanxi, inhibit the vegetation increase in northern part of Xinjiang and the central part of Inner Mongolia. Climate change negatively affect the NDVI in northeast of China and the north of Xinjiang, positively in the eastern part of Inner Mongolia and Tibet Plateau、southern part of Shanxi and Gansu. The increasing trends in potential NPP and NPP residual suggested climate change and human activities made positive effect on vegetation NPP, with the slopes of 0—10gC/m2/y2 accounting for 68.59% and 57.03%, respectively, distributed in eastern part、central part of North of China. Human activities influenced negatively on the vegetation growth in north parts of Xinjiang and northeast part of Inner Mongolia. |
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