长江源区高寒生态与气候变化对河流径流过程的影响分析

Impacts of Alpine Ecosystem and Climate Changes on Surface Runoff in the Headwaters of the Yangtze River

近40 a来长江源区气候变化剧烈,是青藏高原增温最为显著的地区之一,高寒生态系统与冻土环境不断退化.采用多因素逐次甄别方法与半经验理论方法相结合,基于多年冻土的不同植被覆盖降水-径流观测场观测试验结果,分析了长江源区气候-植被-冻土耦合系统中各要素变化对河川径流的不同影响.结果表明:近40 a来长江源区河川径流呈持续递减趋势,年均径流量减少了15.2%,频率>20%的径流量均显著减少,而>550 m3.s-1的稀遇洪水流量发生频率增加;气候变化与高寒草甸覆盖变化对源区径流变化的影响较大,分别占5.8%和5.5%;气候与植被覆盖变化对径流的显著影响是与冻土耦合作用的结果,但冻土环境与冰川变化对径流的贡献尚不能准确评价.高寒沼泽湿地和高寒草甸生态系统对于源区河川径流的形成与稳定起到关键作用,这两类生态系统的显著退化是驱动河川径流过程中变差增大、降水-径流系数减少以及洪水频率增加的主要原因.保护源区高寒草甸与独特的高寒湿地生态,对于维护源区水涵养功能和流域水安全意义重大.

In recent 40 years, the alpine ecosystem and permafrost were continuingly degraded under climate warming. Based on the precipitation-runoff yield tests in permafrost regions with varied vegetation coverage, some sub-experiential methods and multi-actor distinguishing method were used in this paper to analyze the impacts of climate, vegetation and permafrost changes on surface runoff. The results show that the annual average runoff decreased by 15.2%, and the runoff with frequency of more than 20% decreased distinctly. However, the frequency of runoff more than 550 m3/s increased.＇ Changes of climate and alpine vegetation coverage contribute to the runoff decrease by 5. 8% and 5. 5%, respectively. Whereas, the impacts of permafrost and glacier changes on surface runoff are hard to estimate. It is clear that the impacts of climate and vegetation changes on runoff result from an integrated effect that includes permafrost change. In the headwaters, the ecosystem degradation of alpine meadow and swamp meadow was the key factor to result in variation of runoff, precipitation-runoff coefficient decrease and flood frequency increase. Therefore, to protect the alpine meadow and swamp meadow ecosystem from degradation has an important function in water regulation of the Yangtze River.