论干旱区非降水性陆面液态水分分量及其与土壤水分的关系

On the Non-rained Land-surface Water Components and Their Relationship with Soil Moisture Content in Arid Region

雾、露水(或霜)、土壤吸附水、蒸馏水、毛管抽吸水、植物吐水等陆面液态水分分量是表层土壤的重要水分来源,在干旱和半干旱地区其贡献甚至超过了降水量,具有重要的水文学和生态学意义。在综合归纳以往陆面水分过程研究成果的基础上,分别从来自大气的向下水分输送过程和来自土壤的向上水分输送过程,分析各种非降水性陆面液态水分分量的输送特征和形成机制,给出区分和判别各种非降水性陆面液态水分分量的依据,探讨陆面液态水分分量与土壤水分、土壤水分参数和陆面蒸散之间的关系。

The components of land-surface water, including fog water, dew water （or frost water）, soil-adsorbed water, distilled water, capillary water, guttation, etc, are the important water resources of surface soil and of important ecological and hydrological significance, especially in arid and semiarid regions where their contributions may exceed precipitation. These non-rained components of land-surface liquid water, on the one hand, are closely related to soil moisture content, soil particle size, soil organic matter content, soil surface area and soil thermal properties, on the other hand, are relevant to local micrometeorological variables, such as soil temperature, wind speed, and humidity and its gradient. In this paper, the formation mechanism and transport features of the non- rained components of land-surface water are analyzed based on the synthetic research results published in recent years. Then the criteria used to distinguish all of the non-rained components of land-surface water are given. Finally, the relationships between non-rained components of land-surface water and soil moisture, soil hydrological parameters and evapotranspiration are discussed. The results show that the formation and transport of non-rained components of land-surface liquid water are rather complicated. Moreover, there are many technical difficulties in field observation. For these reasons, the non-rained components of land-surface water are commonly referred to and studied without distinction, which often brings errors and confusions. Theoretically, there are currently two available approaches to identify and distinguish these components ： either through the calculations and judgments of a number of key indicators of atmospheric physics, or through the observed change of soil moisture content or leaf water. However, as mentioned above, many problems are accounted in practical observation and calculation. Conversely, accurate measurement of the amount of surface moisture change and rational calculation of various physical indicators is still a challenge research work, and many problems need to be solved. From a perspective of surface water cycle, the overall trend of soil moisture content is undoubtedly affected by the variety of non-rained liquid water components on land surface. The soil properties affect the evapotranspiration, particularly soil moisture content. In arid regions, non-rained components of land-surface liquid water play more significant role in the variation of soil moisture content, which is based on the fact that the amount of surface water from these non-rained components is almost the same as or even higher than that from direct precipitation, and they are also regarded as the dominant factors regulating the daily and annual variation of topsoil moisture content. In the arid and semiarid regions, topsoil moisture content is very low, and the roots of some drought-resistant plant species, such as Populus euphratica, can extent to as deep as 3 -5 m; thus shallow groundwater can be effectively absorbed by plants. Membrane water is basically loose bound water, and its density is very low. Therefore, water can flow slowly from thin part to thick one. Studies show that soil moisture content may be jointly affected by mechanical constraints including molecular attraction, capillary suction and forces of gravity and evaporation. Because of the change of soil moisture molecules from the variation of soil temperature, the evapotranspiration processes of soil moisture change accordingly; the eco-logical significance is also quite different under different climatic conditions. In many cases, however, concerns on the part of soil moisture obtained from adsorption process, which in fact is an important component of soil water in arid region, are far not enough. In arid and semiarid areas, soil water from adsorption process is sometimes more important than the dew drop. Although most of this part of soil water can not directly be used same as dew drop, with the soil adsorbing water involved in the water cycle, other components may play a better role in the ecological benefits.