Abstract Assessing how forest disturbance and climate variability affect streamflow components is critical for watershed management, ecosystem protection, and engineering design. Previous studies have mainly evaluated the effects of forest disturbance on total streamflow, rarely with attention given to its components (e.g., base flow and surface runoff), particularly in large watersheds (>1000 km2). In this study, the Upper Similkameen River watershed (1810 km2), an international watershed situated between Canada and the USA, was selected to examine how forest disturbance and climate variability interactively affect total streamflow, baseflow, and surface runoff. Baseflow was separated using a combination of the recursive digital filter method and conductivity mass balance method. Time series analysis and modified double mass curves were then employed to quantitatively separate the relative contributions of forest disturbance and climate variability to each streamflow component. Our results showed that average annual baseflow and baseflow index (baseflow/streamflow) were 113.3 ± 35.6 mm year−1 and 0.27 for 1954–2013, respectively. Forest disturbance increased annual streamflow, baseflow, and surface runoff of 27.7 ± 13.7 mm, 7.4 ± 3.6 mm, and 18.4 ± 12.9 mm, respectively, with its relative contributions to the changes in respective streamflow components being 27.0 ± 23.0%, 29.2 ± 23.1%, and 25.7 ± 23.4%, respectively. In contrast, climate variability decreased them by 74.9 ± 13.7 mm, 17.9 ± 3.6 mm, and 53.3 ± 12.9 mm, respectively, with its relative contributions to the changes in respective streamflow components being 73.0 ± 23.0%, 70.8 ± 23.1% and 73.1 ± 23.4%, respectively. Despite working in opposite ways, the impacts of climate variability on annual streamflow, baseflow, and surface runoff were of a much greater magnitude than forest disturbance impacts. This study has important implications for the protection of aquatic habitat, engineering design, and watershed planning in the context of future forest disturbance and climate change.

中文翻译：

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森林干扰和气候变异对大型森林主导流域内径流成分的累积影响

摘要 评估森林干扰和气候变异如何影响河流流量成分对于流域管理、生态系统保护和工程设计至关重要。以前的研究主要评估森林干扰对总径流的影响，很少关注其组成部分（例如，基流和地表径流），特别是在大流域（> 1000 平方公里）。在这项研究中，选择位于加拿大和美国之间的国际流域上 Similkameen 河流域（1810 平方公里）来研究森林干扰和气候变异如何相互作用地影响总流量、基流和地表径流。使用递归数字滤波器方法和电导质量平衡方法的组合来分离基流。然后采用时间序列分析和修改后的双质量曲线来定量分离森林干扰和气候变化对每个流量分量的相对贡献。我们的结果表明，1954-2013 年平均年基流和基流指数（基流/径流）分别为 113.3 ± 35.6 mm 年-1 和 0.27。森林干扰使年流量、基流和地表径流分别增加了 27.7±13.7 毫米、7.4±3.6 毫米和 18.4±12.9 毫米，其对各流量分量变化的相对贡献分别为 27.0±23.0%、29.2±23.1 % 和 25.7 ± 23.4%，分别。相比之下，气候变率分别使它们减少了 74.9 ± 13.7 mm、17.9 ± 3.6 mm 和 53.3 ± 12.9 mm，其对各个水流分量变化的相对贡献为 73。分别为 0 ± 23.0%、70.8 ± 23.1% 和 73.1 ± 23.4%。尽管以相反的方式工作，气候变率对年度径流、基流和地表径流的影响比森林干扰影响要大得多。本研究对未来森林干扰和气候变化背景下的水生栖息地保护、工程设计和流域规划具有重要意义。