祁连山高寒山区凝结水时空动态过程

Condensation water is consisted of dew, frost, fog and soil condensation water in the narrow sense. Due to dramatical change of hydrothermal regime in near-surface atmospheric of the Alpine region, condensation occurred frequently and a large quantity of water is involved in this process. As a vital role of hidden water resource, though condensation water does not directly participate in the runoff process of the hydrological cycle, it is much more significance to the fragile ecological stability and eco-hydrological processes of cryosphere sustained-release. Condensation water in different underlying surface (alpine grassland, alpine meadow, alpine shrub, swamp meadow and alpine desert) of the Alpine region is mainly studied and following three questions will be analysed in this project. 1) Comparison the quantity of condensation water at different underlying surface and altitude gradient effect of condensation water on spatial distribution. 2) Relationship between meteorological factors and condensation water in the Alpine region, and the influence of meteorological factors on the change process of condensation water. 3) Interaction between processes of evaporation and condensation. We intend to adopt standard fog collector (SFC), automatic weighing lysimeter, micro-lysimeter, combined with Eddy Covariance and meteorological gradient observation. Through these experiments, the condensation water quantity of different underlying surface in the alpine region can be preliminarily figured out. The processes of evaporation and condensation in shallow layer soil will be studied. The spatial and temporal feature of condensation water in Hulu watershed will be revealed. The amount of contribution of the condensation water to water resources and ecological significance in the Alpine region will be explored.

狭义上的凝结水，应该包括露水/霜、雾水、土壤凝结水。高寒山区近地表大气水热状况变化剧烈，凝结过程频发且水量较多。作为重要的隐性水资源，尽管其不直接参加高寒山区水文循环的产汇流过程，但对于维系高寒山区脆弱生态系统的稳定和冰冻圈生态水文过程的缓释具有重要意义。以高寒山区不同下垫面（高寒草原、高寒草甸、高寒灌丛、沼泽化草甸和高山寒漠）凝结水为主要研究内容，重点分析如下三个问题：1）不同下垫面凝结水量的差异及其海拔梯度效应；2）气象因子对凝结水量及其形成变化过程的影响；3）浅层土壤凝结-蒸发相互作用过程。拟采用标准雾水收集器、自动称重式蒸渗仪和微型测渗计，并结合涡动相关和自动气象梯度塔等仪器，初步认识凝结水量在高寒山区不同下垫面的分布特征，探讨浅层土壤凝结-蒸发相互作用过程，综合分析凝结水的时空动态过程，探究凝结水对高寒山区水资源的贡献量及其生态意义。

高寒山区是我国的生态脆弱区和水资源形成区，近地表大气水热状况变化剧烈，凝结过程频发且水量较多。凝结水作为水平降水，尽管其不直接参加水循环的产汇流过程，但由于凝结水的存在，其消减过程消耗了部分热能，抵消了一部分净辐射，从而在一定程度上降低了实际参与水循环的蒸散发，是冰冻圈水文循环的重要组成部分。凝结水对高寒山区生态系统也有着十分重要的影响，在高寒山区生态形成过程中扮演着重要的角色。对于维系高寒山区脆弱生态系统有重要意义，是冰冻圈生态水文过程的缓释剂。.本项目基于长期野外观测的初步认识，利用和自主设计多种凝结水要素的观测方法，尝试在山区流域对凝结水进行野外观测。观测研究结果表明：① 雾水量和雾水事件的海拔梯度效应非常显著，随着海拔增高，收集的雾水量和雾水事件次数明显增加。② 不同深度和开口方式的微型测渗计观测到5cm的凝结水量最多，土壤中自下向上的水汽吸附占主导，来自于土壤中的水汽吸附凝结大于来自于空气中的水汽凝结，日均霜凝结水量大于日均露凝结水量。③凝结水量在祁连山葫芦沟流域约为29-43mm/a，可达同期降水量的5.12-9.04%，凝结水比降水发生频率更高，是该区水文循环的重要组成部分。④ 高寒山区凝结水主要受近地层空气相对湿度、气温和地表温度的控制。 因此，在凝结水模型构建中应重点考虑这3个微气象因子。.在祁连山高海拔山区，山区水分的来源除了直接降水（雨雪）外，还存在明显的水平降水，即山区凝结水也是水分的一个来源。凝结水在水文循环中也很少直接参与径流过程，但是它们对于植物的生长却具有重要作用，凝结水所带来的水汽是它们可靠的水分来源，而且凝结水也使地面保持湿润状态，减少浅层土壤的蒸发量，相应提高了区域的产流系数。凝结水虽然暂不能作为可开采的水资源量，但凝结水以天为周期不断发生的频率却是大气降水所不可比拟的；凝结水可视为高寒山区水文循环过程的水资源调节量。