Interannual Variation of Vegetation NDVI and Its Temporal and Spatial Response to Temperature and Precipitation in Qilian Mountains

This paper analyzed the temporal-spatial variations and the temporal-spatial responses of vegetation NDVI to the variations of temperature and precipitation in each ten-days period in the whole year, spring, summer and autumn covering 1998 to 2007 based on the SPOT VGT-NDVI data and daily temperature and precipitation data from 11 meteorological stations in Qilian Mountains. The results show that: the maximum values of annual NDVI has been increased with an rate of 3.1%/10a and the greening area, stable area, and degraded area account for 70.21%, 21.44% and 8.35% of the total area in Qilian Mountains, respectively. In Qilian Mountains, the response of vegetation NDVI to the variation of temperature is greater than to that of precipitation, vegetation NDVI maximally responds to the variation of temperature and precipitation with a lag of about 20 days. The response of vegetation NDVI to temperature and precipitation is the greatest in autumn, and the lag time is longer in summer. The maximum response of vegetation NDVI to the variation of temperature and precipitation is greater in central parts than in the eastern and the western Qilian Mountains. There is more lag time of vegetation NDVI to the variation of temperature and precipitation in the western and central parts, while less in the eastern.