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

本研究旨在通过实验和数值模拟来阐明干旱半干旱地区裸地蒸发与盐碱化的关系。结果表明：(1)实验中，利用中国西部沙丘沙地建立沙柱，在沙柱上表面施加可控的大气条件(温度、湿度和辐射)，使含水率剖面(田间持水量)初步均匀。1)土壤颗粒中溶解的液态水、水蒸气和溶质的行为相似，蒸发速率与时间的平方根成反比。2)应用辐射通过向下输送水蒸气来抑制蒸发。3)干燥锋面前的干燥区有较高的盐渍化，导致其水蒸气密度下降，但由于结晶作用，对水蒸气输送的阻力没有增加。4)在模拟夜间(无辐射湿空气)和白天(辐射干燥空气)的周期性大气条件下，沙面附近蒸发凝结的周期性发生在蒸发过程中起着重要作用。(2)利用新建立的水分和溶质运动计算格式进行数值模拟，预测了实验中所见的蒸发盐化特征，其解为了解蒸发盐化过程提供了非常有用的信息。

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.