Study On Spatio-temporal Characteristics Of Land Surface Parameters In The Tibetan Plateau Based On MODIS

As a sensitive area of global climate change,Tibetan plateau has unique characteristics in natural environment and resources whose land surface parameters has been a interested research area for meterorologist and geographer. In this paper spatio-temporal distribution of vegetation index and LST in Tibetan plateau are comprehensively analysised on the basis of MODIS vegetation index and land surface temperature products, then their correlation with meteorological parameters, vegetation types, elevation is studied, finally the vegetation coverage in summer of 2006 and 2008 in the Tibetan plateau is estimated using dimidiate pixel model. The main results are shown as follows:1. Spatio-temporal change of vegetion index. The Spatio-temporal distribution pattern of MODIS NDVI and EVI are consistent, showing a decrease trend from southeast to northwest. Green wave propels from southeast to northwest in spring and brown wave reduces from northwest southeast in autumn. Both NDVI and EVI can better reflect spatio-temporal variations and seasonal evolution in Tibetan plateau.2. Correlation between vegetation index and elevation. NDVI and EVI of different vegetation types show different trends and correlation with elevation changes.Vegetation index of woodland has strong negative correlation with elevation and correlation coefficient above -0.96, grassland and alpine vegetation show negation correlation with elevation, meadow and desert are almost uncorrelated with elevation and areas that without vegetation show a strong positive correlation.3. Correlation between vegetation index and meteorological factors. As to the relevance between vegetation index and monthly average temperature and precipitation, herbaceous vegetation is stronger than shrub vegetation, and shrub vegetation stronger than tree vegetation. In Tibetan Plateau, the response of NDVI to monthly average temperature showed a signigicang time lag effect. NDVI of Broad-leaved forest, coniferous forest, shrub and planting vegetation is lagged to precipitation. EVI of all vegetation types has no lag response to monthly mean temperature and precipitation.4. Spatio-temporal change of land surface temperature. The land surface temperature in Tibetan Plateau is high in spring and summer and low in autumn and winter. The lowest temperature of the year appears in snow and ice covering mountains, while the highest temperature in the Qaidam Basin. The land surface temperature is significantly affected by topography, the temperature changes violently in high mountains and smoothly in area of flat terrain. It was concluded that altitude and vegetation type have significant influences on land surface temperature.5. Spatio-temporal change of vegetation coverage. The vegetation coverage of Tibetan Plateau is high in the southeast region and low in the northwest. The mean vegetation coverage of Tibetan Plateau in summer is 35.98% in 2006 and 37.3% in 2008. Vegetation coverage of different types for the broad-leaved forest, coniferous forestshrub, planting vegetation, meadow, grass, alpine vegetation, hungriness, no vegetation. In general the vegetation coverage of the plateau is turning better.