中国不同干湿区植被变化及其与气候因子的关系

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

中国各区植被覆盖和气候特征多样,植被覆盖变化和气候变化及植被对气候因子的响应存在明显的区域差异,研究不同气候区植被变化及其与气候变化的关系可以为各区针对性地应对气候变化、制定植物保护和生态环境修复政策提供科学依据。本文首先基于中分辨率成像光谱仪(MODIS)的土地覆盖数据,根据植被带的分布确定了划分中国干湿区的指标,其次利用归一化植被指数(NDVI)分析不同干湿区域NDVI的时空变化特征,最后探讨了NDVI变化与温度、降水的关系。结果表明:(1)中国区域200 mm、500 mm和800 mm年降水量等值线分别与荒漠/草地、草地/农田、农田(草地)/森林植被带的分界线吻合,气候过渡带对应着植被过渡带,这些等值线作为划分干湿气候区的指标比较合理。(2)中国年平均NDVI从东南向西北递减,从小到大依次为干旱区(0.11)、半干旱区(0.35)、半湿润区(0.57)、湿润区(0.68)。1982~2015年中国大部分区域NDVI呈显著的增加趋势,区域平均的NDVI在干旱区、半干旱区分别以0.002(10 a)^(-1)、0.008(10 a)^(-1)的趋势显著增加,在半湿润区和湿润区也呈现增加趋势,但不显著。(3)四个干湿区的年平均温度和NDVI均呈显著正相关,仅干旱区、半干旱区年降水和NDVI呈显著正相关,半湿润区和湿润区的年降水与NDVI呈微弱负相关。决定系数表明气候因子变化对NDVI变异的解释比例,温度对四个干湿区NDVI时间变化的解释率相差不大,均在30%左右;降水对NDVI时间变化的解释率低于温度,降水对干旱区(18%)和半干旱区(20%)NDVI时间变化的解释率较大,降水主要影响着北方地区植被的生长。(4)月平均NDVI随着温度和降水的增加都有显著的增加趋势,半湿润区的NDVI随温度升高增长的速率(0.026/℃)最快,半干旱区的NDVI对降水最敏感,随降水增多增加的速率为0.027/mm。

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/℃)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.