The Response Study Of EVI To Climatic Factors In Recent 16 Years' Growing Season Based On Grey Relational Analysis In Inner Mongolia Autonomous Region, China

Inner Mongolia Autonomous Region(IMAR)is a major source of rivers,catchment areas and ecological barriers in the northeast of China,related to the nation's ecological security and improvement of the ecological environment.Therefore,studying the response of vegetation to climate change has become an important part of current global change research.Since the existing studies lack detailed descriptions of the response of vegetation to different climatic factors with the method of grey correlation analysis based on pixel,the temporal and spatial patterns and trends of enhanced vegetation index(EVI)are analyzed in the growing season in IMAR from 2000 to 2015 based on moderate resolution imaging spectroradiometer(MODIS)EVI data.Combined with the data of air temperature,relative humidity and precipitation in the study area,the grey relational analysis(GRA)method is used to study the time lag of EVI to climate change,and the study area is finally zoned into different parts according to the driving climatic factors for EVI on the basis of lag analysis.The driving zones quantitatively show the characteristics of temporal and spatial differences in response to different climatic factors for EVI.The results show that:(1)The value of EVI generally features in spatial distribution,increasing from the west to the east and the south to the north.The rate of change is 0.22/10 °E from the west to the east,0.28/10 °N from the south to the north.During 2000-2015,the EVI in IMAR showed a slightly upward trend with a growth rate of 0.021/10 a.Among them,the areas with slight and significant improvement accounted for 21.1% and 7.5% of the total area respectively,ones with slight and significant degradation being 24.6% and 4.3%.(2)The timelag analysis of climatic factors for EVI indicates that vegetation growth in the study area lags behind air temperature by 1-2 months,relative humidity by 1-2 months,and precipitation by one monthrespectively.(3)On the whole,EVI's response to precipitation is higher than that to air temperature.In terms of ecological details,in forest ecological areas such as coniferous forest and broad-leaved forest,EVI's response to precipitation and relative humidity are higher than that to air temperature.In grassland,meadow and other grassland ecological areas,EVI's response to precipitation is higher than that to air temperature and relative humidity.Coniferous forests,broad-leaved forests,grassland,meadows and marshes are more sensitive to climate change.(4)The response of vegetation EVI to precipitation is the highest in the area below 1,950 m in IMAR,followed by air temperature and relative humidity.While EVI in the area above 1,950 m is more dependent on air temperature than relative humidity and precipitation.With the in increase of elevation,the influence of air temperature on vegetation change in IMAR gradually increased,and the response of vegetation to precipitation gradually decreased.(5)During the growing season,the EVI of precipitationdriving zone(21.8%)inIMAR is much larger than that in the air temperaturedriving zone(8%)and the relative humiditydriving zone(11.6%).The growth of vegetation in IMARgenerally has the closest relationship with precipitation.The growth of vegetation does not depend on the change of a single climatic factor.Instead,it is the result of the combined action of multiple climatic factors and human activities.