Effects of forest cover type and ratio changes on runoff and its components

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Changes in forest cover can affect not only the total runoff from a watershed, but also the runoff components (e.g., surface runoff, interflow, groundwater flow). In this study, based on the WetSpa model simulation method and the recursive digital filtering (RDF) method, the Banchengzi watershed in the mountainous region of Beijing, China, was selected to investigate how changes in forest cover type and cover percentage affect total runoff, surface runoff, interflow, and groundwater flow through scenario settings. Our results show that the difference between the WetSpa model and the RDF method for separating runoff components is small, with only 4.7% and 0.4% difference between the calibration and validation periods. Total runoff in different forest types followed the order shrub forest > coniferous forest > mixed forest > broadleaf forest. Regarding runoff components, the proportions of baseflow (sum of interflow and groundwater flow) to total runoff were 61.1% and 60.8% for broadleaf and mixed forests, which was significantly higher than those of 53.0% and 43.1% for coniferous and shrub forests. However, the proportion of shrub forest baseflow was high in wet years, and that of broadleaf forest baseflow was high in normal and dry years. The proportions of interflow and groundwater flow from various forest cover types to total runoff continued to increase with increasing forest cover rate. Our results have important implications for the implementation of afforestation projects and forest conservation programs, contributing to water resource regulation and ecosystem protection in watersheds.