The Relationship Between Vegetation Index And Climate Factors In Arid And Semi-Arid

Based on GIMMS NDVI3 g dataset(from 1982 to 2013), MODIS NDVI dataset(from 2001 to 2010), CRU high spatial resolution data of temperature and precipitation, temporal and spatial characteristics and the correlation between NDVI and climate factors were studied. Combined with temperature and precipitation data, the relationship and response between vegetation coverage and climate change were analyzed. And by using of daily meteorological data from 1982 to 2010, GIMMS NDVI3 g data and CPC soil moisture data, a comparative analysis of precipitation, effective precipitation, relative humidity and soil moisture at four stations of northwest China were studied, as well as their correlation with NDVI. The main conclusions are as follows:(1) From 1982 to 2013, the precipitation and temperature in most global arid and semi-arid areas showed an increasing trend, the temperature in northern hemisphere changed significantly greater than it in southern hemisphere and it rose relatively greatly in semi-arid areas(0.01- 0.04 ℃/a). The NDVI value in global arid and semi-arid area showed a trend of fluctuations in growth, and the growth trend was faster in northern hemisphere than southern hemisphere.(2) There was a positive correlation overall between climate factors and NDVI in arid and semi-arid areas, the effect of temperature on vegetation was greater than precipitation. It showed a significant positive correlation between NDVI and precipitation in growing season(from March to November in northern hemisphere, and from September to May in southern hemisphere)(R>0.449), but negatively correlated in winter, and their relevance perform weakest. The correlation between NDVI and temperature had a good performance in spring. and their correlation was significantly positive in arid and semi-arid regions at high latitudes in northern hemisphere, while their correlation presents negative at low latitudes.(3) The correlation between climate factors and NDVI was extremely significant. Further more, there existed significant lag effect between NDVI and climatic factors, but the hysteresis effect of temperature was greater than precipitation.(4) In recent 10 years, the NDVI has a good variation trend in Northwest China and the vegetation conditions has been improved. The NDVI interannual variability presents a fluctuation type growth trend(the maximum NDVI between 0.523-0.587). According to the research of correlation between NDVI and climate facters of different vegetation types, the influence of precipitation for various types of vegetation was more apparent than temperature in the northwest region. While for the influence of climate factors on NDVI in mixed forest, there was little difference between temperature and precipitation, and the influence of temperature was more obvious than precipitation in growing period.(5) Through the analysis of four typical stations in northwest China,we found that the influence of moisture factors on NDVI at each station was different. The effect of effective precipitation and soil moisture on NDVI was larger than other factors(the correlation coefficient were about-0.017 to 0.705 and 0.082 to 0.590), and followed by precipitation. Relative humidity had the minimum influence(the correlation coefficient was between-0.347 and 0.157).(6) From the monthly analysis for correlation, we found that the impact of each water factor for NDVI sorted as: precipitation> effective precipitation> soil moisture> relative humidity.