Impact Of Different Vegetation Ecoregions To Temperature Variability In China Since 1982 And Its Possible Cause

This study classifies various ecoregions based on the climatological Normalized Difference Vegetation Index (NDVI) values in China. Vegetation variability, air temperature variability, and their possible relationship in each season of growing season are analyzed. Moreover, possible physical processes of the relationship between vegetation and air temperature are investigated. The main conclusions are summarized as follows:(1) In the past three decades, there is a decreasing spatial distribution of vegetation from east to west in China, and a certain extent of vegetation destruction in Northwest China, the eastern part of Northeast China and along the Yangtze River.Besides, there is an obvious vegetation recovery from Hetao and North China to southern part of Northeast China.(2) Since 1982, the growing season air temperature in China has shown a steady and stable warming, and there is a significant negative correlation between the long-term trend of air temperature and the vegetation conditions. In other words, the lower the vegetation greenness is, the stronger the warming trend is. Moreover, it is worth noting that the negative correlation is the most remarkably in mean minimum air temperature and in all growing season and summer.(3) In all ecoregions, the long-term trend of air temperature is affected by changes of albedo and cloud cover. In the sparse vegetation regions, the increased albedo because of vegetation destruction leads to a decrease in latent heat flux and an increase in sensible heat flux, indicating the warming trend. In the dense vegetation regions, the decline in albedo because of vegetation greening leads to the increase of evaporative cooling, which slows the rate of increase of the whole air temperature.(4) Vegetation destruction in sparse vegetation regions causes higher albedo,reducing the absorption of solar shortwave radiation, cancelling the increase of incoming radiation due to less cloud cover in daytime. Meanwhile, lower emissivity reduces outgoing longwave radiation and thus raises temperatures during nighttime.Opposite in dense vegetation regions.(5) Speed of warming slows down in most regions of China since 2000, and the relationship between the long-term trend of air temperature and the vegetation conditions also has become not remarkable. The possible reason is the phase change of PDO and AMO in different decades and the weakening relationship between air temperature variability and local vegetation activity.