三峡库区小流域景观格局变化洪枯径流效应及归因分析

Runoff extreme responses to watershed landscape pattern changes and their attribution analysis in the Three Gorges Reservoir Area

厘清景观格局变化与洪枯径流的关系,对流域生态建设和水资源调控的协同推进具有重要支撑作用。以我国生态脆弱的三峡库区东里河流域为例,综合运用SWAT(Soil and Water Assessment Tool)模型、景观格局指数和随机森林等方法,从全流域和子流域角度分析了景观格局变化的洪枯径流效应,从景观组成和景观空间配置等多因素角度揭示了洪枯径流驱动机制。结果表明:(1)2000—2020年,全流域优势景观为林地和耕地,面积分别增加了3.76%和1.82%,景观聚集度上升,景观多样性和复杂程度下降;子流域优势景观与全流域基本一致,但斑块密度(PD)、最大斑块指数(LPI)和蔓延度指数(CONTAG)变化更为剧烈。(2)相比2000年,2020年景观格局下全流域洪枯径流以下降为主,最大1d径流(Max1d)下降了4.44%,枯水径流降幅均超40%。典型子流域的洪水径流变幅均高于全流域,而枯水径流变幅与全流域相当。(3)2000—2020年,景观格局对洪枯径流的调节能力减弱,其中景观组成的贡献率下降了0.84%—7.39%,景观空间配置的贡献率下降了1.63%—3.89%,这主要是因流域林草景观组合衰退,以及景观呈聚合发展所致。研究结果可加深对流域景观格局演变和生态水文过程的理解,亦可为流域生态建设和生态修复提供科学依据。

It is important to identify the relationship between runoff extremes and landscape pattern because it benefits for collaborative promotion between ecological construction and water resources regulation within a basin.As one of the most important ecologically fragile area in China,the Three Gorges Reservoir Area experienced ecological construction during the last twenty years.In this study,the Dongli River Basin,within northeastern part of the Three Gorges Reservoir Area,was taken as an example.Several methods,including the SWAT(Soil and Water Assessment Tool)model,landscape pattern index,Pearson correlation analysis and Random Forest,were used to analyze runoff extremes response to landscape pattern changes.And then,runoff extremes of driving mechanism were investigated from the perspective of the whole basin and typical subbasin.The results showed as following:(1)Within the whole basin,forest and cropland were the dominant landscapes,area of which increased by 3.76%and 1.82%from 2000 to 2020,respectively.Its landscape became aggregative while landscape diversity and uniformity declined.The dominant landscapes within the subbasin were similar to that within the whole basin.Changes in patch density(PD),largest patch index(LPI)and contagion index(CONTAG)were more dramatic than those of the whole basin from 2000 to 2020.(2)Four indices,including the maximum 1 day(Max1d)runoff,the maximum 7 day(Max 7d)runoff,the minimum 1 day(Min1d)runoff,and the minimum 7 day(Min7d)runoff,were selected as runoff extremes.Within the whole basin,runoff extremes mainly showed decreasing tendency under the landscape pattern changes from 2000 to 2020.Among them,Max1d decreased by 4.44%while Min1d runoff and Min7d declined more than 40%.Due to landscape changes from 2000 to 2020,the changes of Max1d and Max7d within the typical subbasin were higher than these within the whole basin.The changes of Min1d and Min7d within the typical subbasin were similar to these within the while basin.Runoff extremes within the typical subbasin are hinger than these within the whole basin.(3)The regulation ability of landscape pattern on runoff extremes became weak from 2000 to 2020.Due to degradation in forest-grass landscape combination and aggregation in landscape spatial configuration,contribution rate from landscape composition decreased by 0.84%—7.39%and contribution rate from landscape configuration decreased by 1.63%—3.89%.The results can deepen the understanding of the hydrological process to landscape pattern,which can provide scientific basis for the ecological construction and restoration for the Three Gorges Reservoir Area.