长江经济带降雨侵蚀力与NDVI耦合协调关系时空变异分析

    Spatial-temporal variability analysis of the coupling coordination relationship between rainfall erosivity and NDVI in the Yangtze River Economic Belt

    • 摘要: 为探究长江经济带降雨侵蚀力和植被覆盖关系变化特征及其对土壤侵蚀风险的耦合作用,该研究基于逐日降水数据和逐月NDVI数据,使用日尺度的降雨侵蚀力计算模型和Mann-Kendall趋势检验方法分析了长江经济带月尺度的降雨侵蚀力和NDVI时空演变特征,并通过耦合协调度理论和Pettitt突变点检验识别了降雨侵蚀力与NDVI耦合协调关系的时空变异特征,最后讨论两者之间耦合协调关系变化的原因。结果表明:1)1965-2019年,7-10月长江经济带多年平均降雨侵蚀力在全区空间上分布比较均匀,其他月份多年平均降雨侵蚀力均呈现从东南向西北减少的空间分布格局。东部地区7月和9月的降雨侵蚀力呈现显著增加趋势(P<0.05);2)不同月份NDVI在1999-2019年间显著增加的总面积比例均超过长江经济带总面积30%,NDVI显著减少面积主要在东部地区,该地区土壤侵蚀风险较大;3)降雨侵蚀力与NDVI耦合协调度的多年平均值呈现东高西低的空间分布格局,耦合协调程度整体较低,耦合协调度显著减少的区域主要位于中部和西南部,显著增加的区域主要位于东部;4)长江经济带东部地区面积占比较小的常绿针叶林、常绿阔叶林、混交林和郁闭灌木林等林地面积的显著减少可能是引起耦合协调度显著增加的重要原因。该研究成果将有助于进一步了解长江经济带土壤侵蚀风险的认识,在空间上合理增加林地建设可以保护长江经济带生态环境、水土流失防治。

       

      Abstract: Abstract: Rainfall erosivity and vegetation cover are two of the most important factors in regional soil erosion. The greater the rainfall erosivity is, the more favorable the soil erosion is, whereas, the better the vegetation coverage is, the less favorable the soil erosion is. Moreover, the Yangtze River Economic Belt has been a prominent ecological and national strategic area in China. It is of great practical significance to determine the relationship between rainfall erosivity and vegetation cover, in order to protect the ecological environment. In this study, the daily-scale rainfall erosivity model and the Mann-Kendall trend test were applied to analyze the temporal and spatial evolution of monthly-scale rainfall erosivity and NDVI using daily precipitation and monthly NDVI data. The Pettitt test and coupling coordination degree theory were then used to identify the temporal and spatial variation of the coupling coordination relationship between rainfall erosivity and NDVI. Finally, the reasons were proposed for the change of the coupling coordination relationship between them. The results showed that: 1) Multi-year average rainfall erosivity from July to October was evenly distributed in the whole region, while there was a decrease from the southeast to the northwest in the rest months from 1965 to 2019. A significant increasing trend of rainfall erosivity was also found in the eastern region in July and September (P<0.05). The rainfall erosivity in the central region showed a significant decrease in January, whereas, there was a significant increasing in the central and southern regions in March. The rainfall erosivity in the southwest showed a significant decrease trend in May. 2) On a multi-year scale, the NDVI of the whole gradually increased from June to September, and it reached the highest level in August. The ratio of the area where the NDVI increased significantly in different months to the total area of the study area all exceeded 30% (P<0.05) from 1999 to 2019. The regions with the significant NDVI increase were distributed mainly in the southwest, central and southern regions. But, the NDVI in the eastern region decreased significantly, where the soil erosion risk was also high. 3) There was a high multi-year average in the coupling coordination degree of rainfall erosivity and NDVI in the east, but a low in the west. A significant decrease was detected in the coupling coordination degree in the central and southwestern regions, while a significant increase was in the eastern regions (P<0.05). The significant change-points were found in the coupling coordination degree of rainfall erosivity and NDVI, which were distributed mainly in the southwest, central and eastern regions in the occurrence period from 2003 to 2014. 4) The reduction of forest area (such as evergreen coniferous forest, evergreen broad-leaved forest, mixed forest, and closed shrub forest) was the important reason for the significant increase of coupling coordination degree in the east, indicating a high percentage of vegetation cover but a very small percentage of the area. Consequently, it is a high demand to rationally increase the forest land in space pattern for the ecological environment. The finding can greatly contribute to further understanding the risk of soil erosion in the Yangtze River Economic Belt.

       

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