基于长时间序列NDVI的黄土高原延河流域及其沟壑区植被覆盖变化分析

Analysis of Vegetation Cover Change in Yanhe Basin and Its Gully Area on the Chinese Loess Plateau Based on Long Time Series NDVI

为探究退耕还林(草)等生态工程实施后延河流域坡面与沟壑地貌区的植被恢复情况,基于长时间序列NDVI和降雨数据,采用趋势分析法、Pettitt突变点分析和残差分析以及人工交互样本法对2000—2019年延河流域以及流域坡面和沟壑区植被NDVI变化特征进行了分析。结果表明:(1)2000—2019年延河流域植被恢复明显(年均趋势率为1.30%),但呈现分段特征,其中2000—2008年植被覆盖恢复迅速(年均趋势率为2.00%);2009—2019年植被覆盖恢复速度有所减缓(年均趋势率为0.70%),且部分区域出现退化。(2)2000—2019年延河流域的沟壑区域NDVI随着坡面区域NDVI的增加而增加,且相关性较强(R^(2)=0.967),沟壑区域NDVI与坡面区域NDVI数据值相近。(3)2000—2019年延河流域NDVI变化与降雨量的相关性较弱,降雨不是该地区NDVI变化的主导因子。人类活动与延河流域NDVI变化呈正相关关系,相关性较强;人类活动对NDVI年均贡献率为1.29%。研究表明“退耕还林”等生态工程对植被恢复起到了重要作用,且沟壑区植被覆盖随着坡面植被覆盖变化而变化。

The objective of this study is to explore the tendency of vegetation restoration in the sloping and gullying landform areas of the Yanhe Basin after the implementation of ecological projects such as‘Grain for Green’Program.Based on the long-term NDVI and rainfall data,the change and overall trend of vegetation cover in the Yanhe Basin as well as its gully and hilly areas from 2000 to 2019 were analyzed and tested by applying statistical methods including trend analysis method,Pettitt mutation point analysis as well as residual analysis.The results show that:(1)the significant and positive trend of vegetation restoration in the Yanhe River Basin had been observed for the period of 2000 to 2019(Annual trend rate was 1.30%);however,a segmented feature existed in the general trend:the vegetation coverage was rapidly restored in 2000—2008(Annual trend rate was 2.00%)following with a relatively slight increase in 2009—2019(Annual trend rate was 0.70%),and some areas were degraded;(2)there was relatively strong correlation between gully area′s NDVI and hilly slope area′s NDVI(R^(2)=0.967);meanwhile,the NDVI of the gully area simultaneously increased with the increase of the NDVI of the hilly area from 2000 to 2019;(3)correlation analysis suggested that precipitation did not significantly contribute to the change of vegetation cover in the Yanhe River Basin from 2000 to 2019,while,residual analysis indicated that human activities(‘Grain for Green’Program)significantly contributed to the vegetation cover change in Yanhe River Basin,with an annual rate of 1.29%for NDVI.These results show that ecological projects such as‘Grain for Green’Program played the important role in vegetation restoration and the vegetation coverage of gully region simultaneously changed with the change of slope vegetation coverage.