气候和地形对南水北调中线水源区夏季植被覆盖变化影响分析

Influence study of climate and topography on Fractional Vegetation Cover evolution in summer in the water source area of Middle Route of South-to-North Watertransfer Project

南水北调中线工程是我国重要的大规模跨流域调水工程,其水源区生态保护对于整个工程具有重要意义,但水源区生态环境脆弱,特别是近年来受工程实施和气候变暖的影响,区域植被生态安全面临重大挑战。因此,为了掌握水源区植被动态演变规律及其环境响应特征,基于2000-2020年MODIS植被覆盖度(Fractional Vegetation Cover,FVC)、气象和地形等数据资料,采用线性趋势分析、稳定性分析、相关性分析等统计方法,分析南水北调中线水源区夏季FVC的时空特征,探讨植被覆盖变化对气候、地形因子的响应。结果表明:1)水源区夏季FVC存在明显的空间异质性,分布格局整体呈现中间低、两边高,并以库区、汉江为中心逐步向四周增加的特征,但总体以高FVC为主,占比达到73.5%,主要分布在海拔1000 m以上地区。2)水源区夏季FVC从2000-2020年整体呈明显增加趋势,平均增加速率为0.51%/a,其中高覆盖区平均增加速率为1.92%/a,其分布面积也呈显著增加趋势,表明21年水源区植被生态总体呈改善态势。3)水源区夏季91.5%的区域植被得到改善,与近年来水源区大力实施退耕还林和天然林保护工程等生态保护政策有关。72.7%的区域为植被较低稳定区、中稳定区、较高稳定区,与植被改善分布情况基本吻合;80%以上水源区夏季FVC与春季降水、夏季平均气温呈正相关关系,是水源区夏季FVC变化的主导因子;与夏季降水,春、夏季日照时数主要呈负相关关系,但相关性不显著。其中,春季降水对夏季FVC变化影响区域面积最大。4)水源区夏季FVC的分布具有一定的地形梯度特征,随海拔升高呈先上升再下降的趋势,随坡度增加呈上升趋势,但不同坡向的差异不明显;水源区夏季FVC高值区主要集中在高程为1600~2000 m的中高山区与坡度>16°的地区。

The Middle Route of South-to-North Watertransfer Project(MRSNWP)is an important large-scale inter-basin water transfer project in China,the ecological protection of water source area is of great significance to the whole project.However,ecological environment of water source area is fragile,especially in recent years,due to the influence of project implementation and climate warming,regional vegetation ecological security faces great challenges.Therefore,in order to grasp the dynamic evolution of vegetation in the water source area and its environmental response characteristics,it provides a scientific basis for the ecological protection and restoration of the water source area of MRSNWP.Based on the Fractional Vegetation Cover(FVC),temperature,precipitation,sunshine data from 2000 to 2020 and topographic data,the spatial-temporal characteristics of summer-FVC in the water source area of MRSNWP were analyzed by using linear trend analysis,stability analysis and correlation statistics,and the correlation between summer-FVC and climate as well as topographic factors was discussed.The results showed that:There was obvious spatial heterogeneity in summer vegetation coverage in the water source area.The distribution pattern was generally low in the middle and high on both sides,and gradually increased from the center of the reservoir area and the Hanjiang River to the surrounding areas.However,the vegetation coverage was mainly high,accounting for 73.5%,and mainly distributed in the area above 1000 m altitude.The summer-FVC in the water source area showed a significant increasing trend from 2000 to 2020,with an average increase rate of 0.51%/a.The average increase rate in the high FVC area was 1.92%/a,and its distribution area also showed a significant increase trend,indicating that the vegetation ecology was generally improved in the past 21 years.More than 80%of summer-FVC regions were positively correlated with precipitation of spring and mean temperature of summer in the water source region,which were the leading factors of summer-FVC change in the CLPSNWD.And there was weakly negatively correlated with precipitation of summer,sunshine duration in spring and summer.Precipitation of spring had the greatest influence on summer-FVC in the water source region.Average temperature in summer was the leading factor of FVC change in water source region,but it only had significant effect on FVC change in a few regions.The distribution of summer-FVC in the water source region had topographic gradient characteristics,which increased first and then decreased with the increase of altitude,and increased with the rise of slope,but the difference between different slope directions was not significant.The high value of summer-FVC in the water source region was mainly distributed in the medium-high mountain area with an elevation of 1600~2000 m and the area with a slope greater than 16°.