疏勒河源区高山冻土-植被景观对水文过程影响的试验研究

With global warming, permafrost and its ecosystem changed greatly in cold regions. Unlike the permafrost regions in high latitudes with more precipitation, vegetation are sparse in permafrost regions of arid mountain areas. There is little “protective” effect on ice-poor permafrost because of scarcely moss and organic matter, and permafrost changes are mostly driven by climate. Permafrost and vegetation changes would affected the hydrologic process. However, there is little information about how the permafrost effect the vegetation, and how both of them effect the hydrological process. What change would be the runoff in these permafrost regions? Would it decrease or increase with poor-ice permafrost degradation? We want to give the answers to these questions in our proposal. Source regions of Shule River Basin is chosen as the study area in this case, where there was a large areas of permafrost and the simple landscape structure, and all of these are contribute to discover the actual state of affairs. Relationship between vegetation coverage and active layer depth would be analyzed, and also the relationship between productivity and active layer depth, and other influencing factors. Heterogeneity of the permafrost landscape pattern would be known by remote sensing data .Vegetation change in different permafrost conditions would be analyzed using a method of main discussion of impacts each environmental factors. Meanwhile, the experiments of hydrological process would be conducted in 3 typical catchments with different depths of active layer and vegetation coverage. CRHM (Cold Region Hydrological Model) would be used to discuss the eco-hydrological effects in different catchments. Eco-hydrological effects would be explained by simulation under different scenarios with different active layer depth and vegetation coverage in the source regions of Shue River basin. The results would not only make better understanding about the change of vegetation pattern in poor-ice permafrost region, and try to explain the water recycle process in different permafrost landscape, but also provide some scientific evidence to the regional ecological security protection in warmer future.

高山多年冻土植被带是内陆河流域重要的水文单元。冻土及上伏植被共同作用于水文过程，冻土与植被的变化对河川径流有显著影响。正确认识这一景观单元的水文过程，不仅可为准确认识气候变暖影响下高山冻土植被景观带对径流的补给作用奠定科学基础，也是干旱区中下游绿洲水资源持续利用和生态保护的重要科学依据。本项目选择多年冻土覆盖率大（83%），增温幅度明显且景观结构相对简单的疏勒河源区为研究对象，在对不同多年冻土类型区植被与土壤调查的基础上，分析冻土环境与植被的生长关系及影响植被生长的主导因子；同时在3个不同冻土类型区开展坡面与小集水区尺度的冻土水文过程观测试验，利用寒区分布式水文模型模拟分析冻土-植被生态水文效应；进一步在更大空间尺度上（疏勒河源区），通过对冻土-植被景观格局变化的敏感性试验，模拟分析多年冻土退化、植被变化、冻土-植被变化影响下的径流过程，探讨多年冻土退化和植被变化对流域生态水文效应的影响。

多年冻土及其高寒生态系统之间存在着极为密切的依存关系，二者共同作用于多年冻土区的水文过程。我国西北高海拔区多年冻土1986—1995年呈逐渐退化趋势，1996年至今已演变成加速退化阶段。由于高山区观测条件的限制，目前的研究积累还不能明确解释冻土植被带的生态水文过程及其对流域水资源的影响。本项目选择疏勒河源区为具体研究区，以水量平衡为主线，结合野外观测、典型集水区水文过程试验和水文模型，分析了不同冻土-植被景观类型区的生态水文功能。研究结果表明：（1）气候变暖而导致的冻土活动层增厚与土壤含水量的降低是草地退化的主要原因。1986—2019年30年间，冻土分布下线附近高覆盖草地减少明显，在多年冻土与季节冻土边界向多年冻土区延伸1km区域，草地退化尤为明显；（2）在研究区海拔低于3600m的高寒草原非多年冻土区，降雨径流仅在发生大/强降水事件时出现，产流过程主要受降雨事件的强烈程度影响且退水快速，降雨径流基本由超渗地表径流组成，几乎不产生下渗，很难形成壤中流或地下径流，而且蒸散发量几乎占降水量的98%以上；（3）在海拔3900-4300 m的高寒草甸多年冻土带，小集水区的径流深和径流系数均高于非多年冻土带的高寒草原区，产流过程长且相对稳定，壤中流、地下水径流是其主要成分，超渗地表径流所占比例低。蒸散发量约占降水量的93%，对降水调节能力更强；（4）气候变暖背景下的干旱区高寒冻土-植被带会逐渐上移，随着多年冻土的消失或多年冻土埋深的增加，隔水能力变弱，浅根植物由深根植物代替，受当地降水量的影响，土壤层变厚致使土壤水分更多地用于蒸散发，而非像多雨地区那样促进壤中流和地下径流的形成，退化冻土区植被带对降水的调节作用越来越弱。本项目以疏勒河上游山区为例，分析了多年冻土与植被的变化以及对水文生态效应的影响，丰富了寒区科学研究体系，对预测未来高寒山区生态演变与径流变化具有重要意义，可为区域水资源合理开发和生态保护提供科技支撑。