| In this paper, the study areas, the drylands distributed widely in the world. The north and south hemisphere, North America, South America, the continents of Europe and Asia, Africa and Australia have drylands distribution. Vegetation types are rich in drylands, we divided the vegetation into five categories, for example, the forest, vegetation types, savanna, grassland, farmland. Drylands can be divided into four levels, the extreme drought area, the drought area, the semi-arid area, the sub-humid drought area. Influenced by global change, the degree of drying is increasing and the great changes of vegetation have taken place in drylands. Due to vegetation ecosystem in drylands is sensitivity, vegetation works as an indicator of climate change, and can be more sensitive to respond to climate change. Area of the vegetation in drylands is more sensitive to global climate change. Due to fluctuations in the global climate change and human activities on the ecological environment influence degree enhancement, causes the vegetation in drylands is also in the event of a significant change, such as vegetation degradation phenomenon is more obvious, the land desertification is becoming more and more serious ecological problems, such as increasingly significant, the security and stability of ecosystem is under threat, so arid ecological environment problem more and more attention by the international society.Based on the MODIS vegetation index data, the land surface temperature data, and studies the MERRA reanalysis data arid areas in 2002-2011 global vegetation coverage change in arid areas, from two aspects of the global surface temperature and precipitation the affecting factor on the changes of vegetation in arid areas is analyzed.In this paper, the main research work and the conclusions are as follows:(1) We analyzed arid areas in 2002-2011 global drylands and temporal variation characteristics of vegetation index, at the same time from four level of drought, north and south hemispheres, five continental scale analysis of the different regions, different types of vegetation change characteristic of vegetation index.Analysis found that ten years a downward trend overall vegetation in arid areas, but the present spatial variation in spatial change trend.EVI mean higher areas are mainly concentrated in the low latitudes and forest vegetation types in northern area of the Eurasia;EVI low average areas are mainly distributed in the south of South America, Africa, and Eurasia, the inland areas of Australia. the vegetation index of four level of drought area is decline; In the northern hemisphere vegetation index declined, the southern hemisphere is on the rise; For five continents vegetation index, only Australia rise, the others all showed a trend of decline; For five types of vegetation, shrubs and sparse grassland showed a trend of rising, the others all showed a trend of decline.(2) We analyzed the global surface temperature from 2002 to 2011 in arid areas, and the spatial and temporal variation characteristics of annual precipitation, and from four level of drought, north and south hemispheres, five continental scale different regions and different types of vegetation were analyzed and the change of surface temperature and rainfall characteristics.Study found that vegetation in arid areas covering 10 years overall surface temperature falling in waves, the annual precipitation change in volatility increased, but the spatial change trend are difference.Higher temperature areas are mainly concentrated in the southern hemisphere of South America, Africa, and Australia;Low temperature area mainly concentrated in the north region of the continent of North America and Eurasia.Annual total rainfall of higher area mainly distributed in low latitudes, near the equator in high latitude area rainfall precipitation is less than near the equator.(3) We analyzed the climate(temperature and precipitation) the impact of the change of vegetation in arid areas.The study found that the temperature, precipitation interannual variability mutual influence vegetation in arid areas, the temperature and vegetation changes are negative correlation, and the changes of precipitation and vegetation is positive correlation, vegetation present spatial heterogeneity of interannual climate response.For four types of drought level arid zone, precipitation level of half arid area, the level of drought area and the influence degree of the level of extreme drought area of vegetation is greater than the temperature influence on vegetation, and humid in the level of drought area temperature influence on vegetation degree should be greater than the impact of precipitation on vegetation.For the north and south hemispheres, the influence degree of the precipitation of vegetation in arid areas is greater than the effect of the temperature.Visible on a global scale and intercontinental scale, as a result of the increase of precipitation in arid areas, especially in North America, South America the main factor of vegetation increased activity and precipitation in arid areas and potential evaporation is the most significant climate variables affecting vegetation, shows that the regional water balance is the most important factors controlling the condition of vegetation.For five continents, the extent of the vegetation in arid areas in Africa and South America bigger climate factors of precipitation, and the Eurasian continent, North America, Australia is strongly influenced by temperature.For different vegetation, grasslands and savanna is strongly influenced by temperature, thickets, greater degree of farmland is affected by precipitation. |
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