植被恢复对青海省北川河流域水循环演变趋势的影响

目的] 研究植被恢复对流域水循环的影响，明确植被恢复条件下流域水资源的演变趋势，为指导干旱半干旱地区开展科学的植被恢复工作提供数据支撑。方法] 结合青海省北川河流域植被覆盖变化及长序列气象、水文数据，分析流域尺度水循环要素的演变趋势，分析植被恢复对关键水循环要素演变的影响作用。结果] 20世纪80年代以来，北川河流域丘陵山区植被覆盖快速增加，仅2000—2019年期间平均增幅14.98%，最大增幅52.2%。1956—2019年，流域年降水量相对平稳，但年径流量呈不显著衰减趋势，平均降幅1.60×10⁷ m³/10 a，流域生态用水量增加是造成径流衰减的主要原因；植被恢复改变了流域大气降水的时空分配，在空间上更多降水用于流域内部生态消耗，减小了对下游的水源供给量，在时间上更多降水参与土壤水—地下水循环，延长了向流域外的排泄周期；地表风速、水面蒸发量、干旱指数等气象要素显著降低。结论] 植被恢复影响下，北川河流域生态用水量增大，径流量衰减，降水—土壤水—地下水循环过程的水量比例增加，流域水源涵养能力不断提高，半干旱的气候条件有所改善。

Effects of Vegetation Restoration on Evolution Trend of Water Cycle at Beichuan River Basin in Qinghai Province

Objective] The impact of vegetation restoration on the water cycle of Beichaun River basin was studied and the evolution trend of water resources in the basin under the conditions of vegetation restoration was analyzed in order to provide data support for guiding scientific vegetation restoration in arid and semi-arid areas.Methods] The evolution trend of water cycle elements at the basin scale was analyzed based on the vegetation cover change and long-term meteorological and hydrological data at Beichuan River basin in Qinghai Province. The influence of vegetation restoration on the evolution of key water cycle elements was analyzed.Results] Vegetation coverage in the hills and mountains of Beichuan River basin had increased rapidly since the 1980s, with an average increase of 14.98% and a maximum increase of 52.2% from 2000 to 2019. From 1956 to 2019, the annual precipitation in the basin was relatively stable, but the annual runoff showed a small decreasing trend, with an average decrease of 0.16 billion m³/10 yr. Increasing ecological water consumption caused by vegetation restoration was the main reason for decreasing runoff. Vegetation restoration had changed the spatial and temporal distribution of precipitation in the basin. In space, more precipitation was used for ecological consumption in the basin, which reduced the water supply to downstream regions. In time, more precipitation participated in the soil water-groundwater cycle, and prolonged the drainage period outside the basin. Vegetation restoration significantly reduced meteorological factors such as surface wind speed, water evaporation, and drought index.Conclusion] Runoff in Beichuan River basin has decreased due to the influence of vegetation restoration. Additionally, ecological water consumption and the proportion of water in the cycle of precipitation-soil water-groundwater has increased, water conservation capacity has continued to increase, and semi-arid climate conditions have improved.