The Variation Of NDVI And Its Relationship With Climate Factors In Ruoergai Wetland At Different Time Scales

Based on the different time series NDVI data, the difference and suitability of GIMMS-NDVI, VGT-NDVI and MODIS-NDVI response to vegetation change in Ruoergai wetland were analyzed in this study, and the work of the variation of NDVI and its relationship with climate in Ruoergai wetland at different time scales were carried out, especially focusing on the long time scale. In order to reveal the change of vegetation in Ruoergai wetland, the annual NDVI change and the response to climate change for the annual averaged NDVI, averaged NDVI in growth season, averaged NDVI of different time period were discussed for the whole region and for the different vegetation types in Ruoergai wetland. The spatial heterogeneity of vegetation change and its relationship with climate factors were also explored. Our results could provide scientific basis for the strategies of ecological protection and for the making full use of wetland resources.The main conclusions as following:The advantage of prominent sensitivity of red spectrum, removing water vapor absorption band in infrared spectrum and higher spatial resolution of MODIS-NDVI and VGT-NDVI, which resulted these two types data are more sensitive to the change of vegetation and more suitable to the study of vegetation than GIMMS-NDVI data in Ruoergai wetland. However, there is no significant difference among the three NDVI data, and the GIMMS-NDVI has longer time series than the other two data, and it still will play an important role on the study of vegetation change;In Ruoergai wetland high NDVI value distributes in the northeast part of Ruoergai county, and low NDVI value in the southwest of Maqu county, southeast of Hongyuan county and northwest of Aba county;The GIMMS-NDVI data was used to investigate the variation of NDVI in Ruoergai wetland from 1982 to 2003. The vegetation activity in this area incresesd with the annual averaged NDVI increased by 5.4% in the 22 years, and the averaged NDVI in the growth season increased 6%. The averaged NDVI from April to May has increased 12.6% from 1982 to 2003, with 5.8% and 2.6% of increase from June to August and from September to October respectivelly. For the different vegetation type, the averaged NDVI in growth season of the grass increased 6.4% from 1982 to 2003, with the forest increased 4.3%. The averaged NDVI in growth season indicates a significant increase at about 45.8% of the whole Ruoergai wetland with the confidence limit of 95%, distributing in the western part of Maqu county, the northern part of Hongyuan county, the east part and the middle part of Aba county;Correlation analysis was carried out between the annual averaged NDVI, the NDVI in growth season, the annual averaged NDVI of different vegetation types with the climate factors. The results show that there is a significant relationship between NDVI with temperature, precipitation and surface temperature, all the three climate factors are the important factors to the vegetation growth activity in Ruoergai area, and temperature plays the most important role among the three climatic factors. For the different type of vegetation, the correlation coefficient of grass is higher than that of forest, which suggests that grass is more sensitive to climate change than forest, may be caused by the biological characters of itself;The correlation coefficient between NDVI in the whole area from April to May with the temperature and precipitation are high, similar with that of the different type vegetation, suggesting that the NDVI increase mainly relates with the temperature and precipitation increasing, and the NDVI increase from June to Augest and from September to October are mainly caused by the increase of temperature and surface temperature.