Vegetation Changes and Their Relationship with Climate Factors in Different Dry/Wet Areas over China

Various regions in China have diverse vegetation covers and climate characteristics, and there are obvious regional differences in vegetation cover change, climate change, and the response of vegetation to climate factors. The study of vegetation changes and their relationship with climate change in different climate regions can provide a scientific basis for responding to climate change and formulating plant protection and ecological environment restoration policies in various regions. First, based on the land cover data of MODIS (MODerate-resolution Imaging Spectroradiometer), the indexes for dividing dry and wet areas in China were determined according to the regions’ vegetation zone distribution. Second, the temporal and spatial variation characteristics of the Normalized Difference Vegetation Index (NDVI) in different dry and wet areas were examined using vegetation index NDVI. Finally, the relation between the NDVI and temperature/precipitation was discussed. The findings revealed that (1) 200 mm, 500 mm, and 800 mm annual precipitation contours in China are consistent with the boundaries of the vegetation zones of barren land and grassland, grassland and cropland, and grassland/cropland and forest, respectively. The climate transition zones correspond to the vegetation transition zones. These lines are reasonable indexes corresponding to dry/wet climate zoning. (2) Annual averaged NDVI in China decreases from southeast to northwest, from small to large, as follows: the arid area (0.11), semiarid area (0.35), semihumid area (0.57), and humid area (0.68). The NDVI increased significantly in most regions of China during 1982–2015. While regional averaged NDVI increases considerably in arid and semiarid areas with trends of 0.002 (10 a)⁻¹ and 0.008 (10 a)⁻¹, respectively, it does not show a substantial increase in semihumid and humid areas. (3) There are significant positive correlations between the annual averaged temperature and NDVI in the four dry and wet areas. The annual precipitation is significantly correlated to NDVI only in arid and semiarid areas, and weak negative correlations are observed in semihumid and humid areas. The coefficients of determination indicate the explanation proportion of changes in climate factors to NDVI variation. The temperature changes explain about 30% of the temporal changes in NDVI in these four dry and wet areas. The explanations of precipitation changes to the temporal changes in NDVI are lower than those of temperature. Changes in precipitation explains greatly to the temporal changes in NDVI in arid areas (18%) and semiarid areas (20%), and it mainly affects the vegetation growth in northern China. (4) The monthly average NDVI exhibits a considerably increasing trend with increasing temperature and precipitation. The increasing rate (0.026/°C) of NDVI in the semihumid area is the fastest with increasing temperature, while that in the semiarid area is the most sensitive to precipitation, with an increasing rate of 0.027/mm with increasing precipitation.