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

通过试验和数值模拟研究了干旱半干旱地区裸地蒸发与土壤盐渍化的关系。获得了以下结果。(1)在实验中，在中国西部的沙丘砂被用来建立一个砂柱和一个受控的大气条件（温度，湿度和辐射）施加在柱的上表面与初始均匀的水分含量剖面（田间持水量）。1)液态水、水蒸气和土壤颗粒溶解溶质的蒸发行为相似，蒸发速率与时间的平方根成反比。2)辐射的应用通过向下输送蒸汽抑制蒸发。3)在干燥锋前的干燥区发生了严重的盐渍化，导致其蒸汽密度下降，但没有看到由于结晶而增加的蒸汽输送阻力。4)在模拟夜间（无辐射和湿空气）和白天（有辐射和干空气）的周期性大气条件下，近沙面蒸发凝结的周期性发生对蒸发过程起着重要作用。(2)采用一种新的水和溶质运动计算方案进行的数值模拟预测了实验中所见的蒸发-盐渍化特征，其解成为理解蒸发-盐渍化过程的非常有用的信息。

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.