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植物生态学报 2003
CORRELATION ANALYSIS OF NDVI WITH CLIMATE AND HYDROLOGICAL FACTORS IN OASIS AND DESERT
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Abstract:
The interactions between vegetation and climate are always an important domain in ecological research. NDVI (Normalized difference vegetation index) is an important index that reflects the radiation_absorbing characteristic of vegetation and the climatic stress action. Since 1990, the relationships between NOAA/AVHRR NDVI and climatic factors have been studied in many papers and the relative conclusions in arid zones differ completely. It is very important to clear up the problem in the application of NDVI to eco_environmental monitoring and research in arid zones. By means of the digital NOAA/AVHRR NDVI images with 1 km spatial resolution and monthly climatic and hydrological data set in Fukang from 1992 to 1996, the correlation of NDVI with climate and hydrological factors are analyzed in oasis and desert respectively in this paper. NDVI images come from AVHRR database of United States Geological Survey, which have been treated with atmosphere rectification, cloud checkout, quality control and maximum value composite every ten days. NDVI images are registered to 0.3-0.7 pixel error according to the mountains and water system map in Xinjiang. Oasis NDVI is clipped with farm boundary in Fukang and desert NDVI is clipped with desert grassland boundary. Monthly NDVI mean values in oasis and desert are calculated respectively with Arcview 3.2. Climate indices include monthly precipitation, monthly maximum atmospheric temperature, monthly minimum atmospheric temperature, monthly average atmospheric temperature, monthly minimum relative humidity, monthly mean relative humidity and monthly sunlight hours. Hydrological indices include monthly surface runoff in Sangonghe basin and monthly mean water table in pluvial fan and alluvial plain. The correlation coefficients of NDVI with all climatic and hydrological factors are calculated with SPSS 10.0. The analysis shows that NDVI values in oasis have different rules of monthly variation from those in desert. Atmospheric temperature, groundwater table and precipitation are significantly correlative with NDVI in oasis, and irrigation is an important factor, which influences oasis NDVI. Correlation coefficients of desert sparse vegetation NDVI with oasis climatic and hydrological factors are insignificant and meaningless in ecological interpretation. In the process of analysis between NDVI and environmental factors in arid zones, the temporal and spatial scale must be strictly corresponding, oasis and desert must be considered respectively and conclusions from oasis NDVI are not adapted to the desert sparse vegetation. The contradictions in the conclusions of foregoing studies come from the confusion of application scope of their results, and the results of oasis NDVI can not represent the rules of the whole arid zone.
