Grassland Vegetation Change Based on MODIS NDVI Data and Climate Information

Monitoring vegetation change is an important aspect to study global climate chan ge. The Normalized Difference Vegetation Index (NDVI) is the most frequently us ed vegetation index to discuss environmental change. It's common to study vegetati on change using the NOAA Advanced Very High Resolution Radiometer (AVHRR) data which are available for more than 20 years, and the EOS Moderate Resolution Im aging Spectroradiometer (MODIS) data with improved quality are also widely used now. MODIS NDVI dataset during 2000—2005 in Xilingol are analyzed. Precipitation, vapor pressure, mean temperature, max temperature, min temperatur e, hours of sunshine are taken as climatic elements to explore the relationship between MODIS NDVI and climatic factors over different types of grassland. Due t o the narrow spectra bands of infrared and near infrared satellite sensors, MOD IS NDVI is sensitive for dynamically monitoring the four types of steppe: Meadow steppe, typical steppe, sandy steppe, desert steppe. As the water conditions of these four typical grassland vary widely, their spectral responses are also sig nificantly different. The vegetation increases on the whole in Xilingol during t he period of 2000 to 2005. Desert steppe decreases while typical steppe increase s for the research area. The global warming trend is obvious in Xilingol. Althou gh the rain doesn't increase much from 2000 to 2005, the grassland grows for t he meadow steppe and the typical steppe, promoted by the increasing temperature and better water conditions. For the sandy steppe and the desert steppe where wa ter conditions are poor, as the increasing temperature accelerates water evapora tion, the vegetation degradation occurs as a result of the worse environment. MODIS NDVI series exhibit obvious correlation with climatic factors. For typical steppe, max temperature is the most related factor with NDVI, and vapor pressur e is the second. For desert steppe, max temperature is the most related factor w ith NDVI, and min temperature is in the second place. Responses of MODIS NDVI to climatic factors lag in time obviously. The lag time for all climatic factors i s -1 stage for typical steppe, and for desert steppe, the lag time for both wate r and mean temperature climatic factors is -1 stage, while the lag time is incon sistent for max temperature and min temperature, which may be caused by the diff erences of soil texture and vegetation types.