基于时序NDVI的三峡库区植被覆盖时空变化特征分析

摘要

基于250 m分辨率的MODIS-NDVI数据,从时间变化和空间变化两方面分析2000年～2015年三峡库区植被变化特征,运用一元线性回归趋势分析方法和F检验方法对三峡库区NDVI的变化趋势进行了定量研究.结果表明:16a来三峡库区NDVI总体上趋于波动增长,年均增长率为0.17％,但在时间和空间上有不同的变化特点.从季节差异上看,春季NDVI增长最快,其次是秋季和冬季,夏季NDVI变化趋势较平缓.从NDVI的空间变化格局上看,NDVI呈显著增加趋势的面积占整个库区面积的14.47％,轻微增加占55.77％,增加区主要分布在库区的北部、东北部、东部及东南部.库区20个县(区)NDVI呈显著增加的面积均大于显著减少面积,其中巫溪、兴山、宜昌、巴东4县的增减面积均在800 km2以上,植被覆盖提升明显;忠县、重庆市区、渝北、长寿4县(区)的增减面积差均低于30 km2,植被覆盖增加相对较慢.库区各类型植被的NDVI均呈上升态势,其中草地NDVI增长最快,阔叶林NDVI显著增加面积占其总面积的比例最高,灌丛NDVI显著增加面积在所有植被类型中最大,退耕还林还草和农业生产模式转型也促使农作物NDVI缓慢增长.%A lot of studies have demonstrated that the NDVI and vegetation cover conditions showed a significant positive correlation,which could well reflect the status of vegetation cover.Thus,NDVI was subsequently used to study the changes in vegetation spatial and temporal dynamics.In this paper,using the 250 m spatial resolution MODIS-NDVI dataset from 2000 to 2015,we analyzed the vegetation variation characteristics in the Three Gorges Reservoir area from the time scale,space change and vegetation types.As to the methodology for analyzing vegetation coverage changes,monadic linear regression trend analysis and F test method were mostly used to analyze time serial NDVI data for quantitative study of NDVI change trend.The results showed that the annual average NDVI of the Three Gorges Reservoir area was rising with fluctuations on the whole,with an average annual growth rate of 0.17％,but some differences existed in time,space and different vegetation classes in the 16 years.Judging from the seasonal difference,the NDVI increased most significantly in spring,followed by autumn and winter,and the change trend of NDVI in summer is gentle.Judging from the spatial variation pattern of NDVI,the area with significantly increased NDVI accounted for 14.47％ in the reservoir,and that with slight increase accounted for 55.77％.The increased areas were mainly distributed in northern,northeast,east,southeast region.Area with NDVI significantly increased area was greater than that with NDVI significantly increased in 20 counties (districts) of the Three Gorges Reservoir area,in which the differences among the area of 4 counties,including Wuxi,Xingshan,Yichang and Badong,were more than 800 km2 and the vegetation cover was significantly improved.The differences in the area of Zhongxian,Chongqing,Yubei,Changshou 4 counties (districts) was less than 30 km2 and the vegetation cover increased relatively slowly.NDVI of all types of vegetation cover possessed rising trend,in which the NDVI of grass increased fastest while the crop was the slowest,and the NDVI significant increased area of broad leaved forest possess the largest proportion of total area,while the NDVI significant increased area of shrub was the largest in all vegetation types.The transformation of cropland to forest and grass and the transformation of agricultural production mode not only promoted the slow growth of crop NDVI,but also contributed to the overall vegetation coverage of the reservoir area.