Study on the Relationship between Evaporation from Bare-Soil Surfaces and Salinization in Arid and Semi-Arid Areas

本研究旨在通过试验和数值模拟，阐明干旱半干旱区裸露土壤表面蒸发与盐渍化的关系。得到了以下结果：(1)试验采用中国西部沙丘砂设置沙柱，在沙柱上表面施加可控大气条件（温度、湿度和辐射），沙柱的含水量剖面（田间容量）初步均匀。1)土壤颗粒中溶解的液态水、水蒸气和溶质具有相似性，蒸发速率与时间的平方根成反比。2)辐射的应用抑制了蒸汽向下输送的蒸发。3)干燥锋前的干燥区出现了高盐渍化，导致其蒸汽密度下降，但未见结晶导致蒸汽输送阻力增加。4)在模拟夜间（无辐射和潮湿空气）和白天（辐射和干燥空气）的周期性大气条件下，沙面附近的周期性蒸发-凝结在蒸发过程中起着重要作用。(2)采用新形成的水和溶质运动计算格式进行数值模拟，预测了实验中观测到的蒸发-盐渍化特征，其解为理解蒸发-盐渍化过程提供了有用的信息。

This research aims at clarifying the relation between evaporation from bare-soil surfaces and salinization in arid and semi-arid areas through an experiment and a numerical simulation. The following results were obtained.(1) In the experiment, dune sand in Western China was used for setting up a sand column and a controlled atmospheric condition (temperature, humidity and radiation) was applied on the upper surface of the column with initially uniform water content profile (field capacity). 1) Liquid water, water vapor and solute dissolved from soil particle behaved in a manner of similarity, and evaporation rate varied inversely as square root of time. 2) Application of radiation suppressed evaporation through a downward transport of vapor. 3) High salinization occurred in a dried zone ahead of the drying front lead descent of its vapor density but increase in resistance to the vapor transport owing to the crystallization was not seen. 4) Under the periodic atmospheric condition simulating night-time (non-radiation and moist air) and daytime (radiation and dry air), periodic occurrence of evaporation-condensation near the sand surface played an important role in the evaporation process.(2) A numerical simulation using a newly formed calculation-scheme for water and solute movement predicted characteristics of evaporation-salinization seen in the experiment, and its solutions became very useful information for understanding the evaporation-salinization process.