淮河流域1999-2018年NDVI时空演变特征研究

Spatial-temporal Evolution of the Normalized Difference Vegetation Index(NDVI)in the Huaihe River Basin from 1999 to 2018

植被是全球碳循环的主要参与者之一,在陆面水分运移和能量传输中发挥着巨大作用。以淮河流域1999—2018年的归一化植被指数(NDVI)时间序列为基础数据,利用Mann-Kendall趋势检验法和经验正交函数分解法(EOF)研究了淮河流域月、季、年等3个时间尺度的NDVI时空演变规律。结果表明:①受流域作物熟制和地形地貌的影响,淮河流域月NDVI的多年平均值整体呈M状,不同子流域NDVI的均值和变化幅度均存在差异性;②在农田面积占比较多的下游,夏、冬两季NDVI呈不显著下降趋势,而在淮河其他3个子流域,四季NDVI均呈上升趋势,尤其是春、秋两季,多为显著上升趋势;③淮河流域年NDVI整体呈显著上升趋势,和全球变绿的趋势是一致的,同时也表明近20年来退耕还林及其他水土保持措施的实施,在淮河流域植被恢复与生态保护工作取得了较好的成效;④淮河流域NDVI空间模态分布整体上呈同增同减,东西部差异较大,植被覆盖度由内陆向沿海逐渐降低的形式。研究成果可为淮河流域植被覆盖特征、生态环境保护等提供参考依据。

Vegetation is one of the main participants in the global carbon cycle and plays an important role in land surface water transport and energy transmission.Based on the normalized difference vegetation index(NDVI)of the Huaihe River Basin(HRB)from 1999 to 2018,the spatial-temporal evolution law of NDVI was studied on three time scales(month,quarter,and year)through the Mann-Kendall trend test and empirical orthogonal function(EOF)decomposition.The following findings are obtained.①Affected by crop maturity and different landforms,the multi-year average values of monthly NDVI in the HRB present an M-shaped distribution as a whole,and there are some differences in the mean value and variation range of NDVI in different sub-basins.②In the downstream area with more farmlands,the NDVI shows an insignificant downward trend in summer and winter,while in other three sub-basins of the river,the NDVI follows an upward trend in all seasons,especially in spring and autumn.③The annual NDVI of the basin exhibits a significant upward trend,which is the same as the global greening trend.This also indicates that returning cropland back to forests and other soil and water conservation measures have achieved remarkable results in vegetation restoration and ecological protection in the basin for the past 20 years.④The spatial distribution of NDVI modes in the HRB shows simultaneous increases or decreases overall,with a great difference existing between the western and eastern areas.Vegetation coverage gradually decreases from inland to coastal.These research results can provide a reference basis for understanding the vegetation restoration characteristics and protecting the ecological environment in the HRB.