用拱棚法对极干旱区沙地水分来源的定性分析

在潜水埋深超过200m的敦煌莫高窟极干旱沙漠区,用拱棚法和微型空气湿度监测仪对流沙水分的时空分布格局进行监测,并对水分的来源进行分析。拱棚膜面凝结水分的持续抽取表明,在典型干旱气候条件下,有源源不断的沙地水分蒸发,其中1.25g.m-2.d-1的水分在膜面凝结。沙地水分的时空动态分布格局表明,存在水分向上运移的温湿度条件。由此判定,除降水之外地下潜水蒸发是沙地水分最基础的来源。实验表明,干沙层虽然对沙地水分蒸发具有极强的抑制作用,但在升温过程中仍存在水分蒸发;在降温过程不但可从下层流沙吸收大量的水分,而且可吸收大气水分。沙地的蒸发量大于来自大气的吸湿量,总有少量的水分流失。沙地水分潜水来源的确定,不但对沙漠化的治理提供了新思路,而且对莫高窟文物的保护具有十分重要的意义。

Qualitative Analysis on Moisture Source in Extreme Arid Dune with Coved Canopy Method

The depth of groundwater table is below 200 m in Dunhuang Mogao Grottoes area,an extreme arid desert area. The spatio-temporal distribution pattern of moisture in sand dune is measured by a minisize air humidity monitor under a coved canopy. There is continuous condensation water on canopy film at a rate of 1.25 g·m~(-2)·d~(-1),which indicates that there exists continuous dune evaporation in this arid condition. The evaporation of groundwater is a principal source in addition to precipitation source. Experiment demonstrates that although dry dune layer severely restrains the moisture evaporation from dune,there is still evaporation during temperature rise;when the temperature comes down,dry sands not only draw moisture from under layers,but also absorb water from atmosphere. The discovery of moisture source in sand dune is significant for the protection of the cultural relics in Mogao Grottoes,and can also provide new thought for desertification control.