Since 1999, large-scale ecosystem restoration has been implemented in the Loess Plateau, effectively increasing regional vegetation coverage. Vegetation restoration has significantly elevated the saturated hydraulic conductivity (Ks) of the near-surface soil layers and increased the vertical heterogeneity of the Ks profile. Many studies have examined the change of runoff due to revegetation, yet the impacts of Ks profile on the soil moisture distribution and runoff generation processes were less explored. In this study, numerical simulations were conducted to investigate how changes in the Ks profile caused by vegetation restoration influenced the hydrological responses at event scale. The numerical simulation results show that the increase of surface Ks caused by vegetation restoration can effectively reduce runoff at event scale. Moreover, the enhancement of vertical heterogeneity of Ks profiles can significantly change the vertical profile of soil water content, prompting more water to percolate into the deep soil layer. When rainfall exceeds a threshold, the accumulation of soil water above the relatively less permeable layer can cause short-term saturation in shallow soil layers, resulting in a transient perched water table. As a result, after the vegetation restoration in the Loess Plateau, though Horton overland flow is still the main runoff generation mechanism, there is a possibility of the emergence of Dunne overland flow under the high vegetation coverage (e.g., NDVI larger than 0.5). This emergence of new runoff generation mechanism, saturation excess runoff, in the Loess Plateau due to the vegetation restoration could provide scientific guidance for water and sediment movement, soil and water conservation practices, and desertification control in the Loess Plateau.

中文翻译：

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典型黄土流域植被恢复对径流生成过程的影响

1999年以来，黄土高原实施了大规模的生态系统修复，有效提高了区域植被覆盖度。植被恢复显着提高了近地表土层的饱和导水率（Ks），并增加了Ks剖面的垂直异质性。许多研究考察了植被恢复引起的径流变化，但很少探讨Ks剖面对土壤水分分布和径流生成过程的影响。在本研究中，通过数值模拟来研究植被恢复引起的Ks剖面变化如何影响事件尺度的水文响应。数值模拟结果表明，植被恢复引起的地表Ks增加可以有效减少事件尺度的径流。此外，Ks剖面垂直异质性的增强可以显着改变土壤含水量的垂直剖面，促使更多的水渗入深层土壤。当降雨量超过阈值时，渗透性相对较差的层上方土壤水的积累会导致浅土层的短期饱和，从而导致短暂的滞留地下水位。因此，黄土高原植被恢复后，虽然霍顿地表径流仍是主要径流生成机制，但在高植被覆盖度（如NDVI大于0.5）下，存在出现邓恩地表径流的可能性。黄土高原因植被恢复而出现的新径流生成机制——饱和过剩径流，可为黄土高原水沙运动、水土保持、荒漠化防治提供科学指导。