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Relationships between vapor condensation, evaporation and salinization near ground surfaces in arid and semi-arid areas.

干旱和半干旱地区近地表水汽凝结、蒸发和盐化之间的关系。

基本信息

批准号：
11650536
负责人：
SHIMOJIMA Eiichi
金额：
$ 2.05万
依托单位：
Daido Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-11650536/
关键词：
arid-and seim-arid areas evaporation vapor condensation salinization experiment numerical simulation 観測データ

项目摘要

By paying attention to the condensation of atmospheric vapor, the relation between soil-surface evaporation and salinization in arid/semi-arid areas was explored through an evaporation experiment from a sand column and a numerical simulation to meteorological data observed in a desert area in West China (HEIFE).Using air-dried dune sand for HEIFE (Case A) and a fine silica sand (Case B), sand columns were set up on the balance, where only in the latter case, a shallow water table of NaCl solution with a high concentration was set. The columns were exposed to ambient air controlled at 65% humidity (corresponding to nighttime) and at 20% (daytime) alternately, where the air temperature is kept constant (25℃) and 550 W/m^2 of heat radiation was applied on the sand surface only at the dry air stage. Locations and movements of the evaporation and condensation zone for both cases were analyzed using information on vapor in the sand columns measured by humid-cups. For Case B the condensation amount at the wet stage was almost equal to the evaporation one at the dry stage, while for Case A, the evaporation was about ten times larger than the condensation and source of its surplus evaporation was the underlying aquifer. Soil water ahead of the evaporation front for Case B was chemically saturated and its concentration behind the front decayed exponentially with depth, while salinization for Case A was much lower.A numerical simulation using a model of heat-moisture-solute movement in the atmosphere-land system was successfully undertaken. And it was known that source of evaporation in that desert was almost rainfall and a spike of solute concentration profiles observed at 〜10 cm deep from the ground surface appeared through the interaction between rain-infiltration and soil-water evaporation.

在关注大气水汽凝结的基础上，通过沙柱蒸发实验和对中国西部荒漠地区气象观测资料的数值模拟，探讨了干旱半干旱地区地表蒸发与盐碱化的关系。柱子交替暴露在湿度为65%(对应于夜间)和20%(白天)的环境空气中，空气温度保持恒定(25℃)，仅在干燥空气阶段才在沙子表面施加550W/m^2的热辐射。利用湿杯测量的沙柱中水蒸气的信息，分析了两种情况下蒸发和冷凝区的位置和运动。对于情况B，湿阶段的冷凝量与在干燥阶段的蒸发量几乎相等，而对于情况A，蒸发大约是凝结的十倍，其过剩蒸发的来源是下伏含水层。B例蒸发锋前方土壤水分化学饱和，蒸发锋后土壤水分浓度随深度呈指数衰减，而A例蒸发锋前土壤水盐渍化程度较低。研究表明，沙地蒸发的主要来源是降雨，通过降雨入渗和土壤水分蒸发的相互作用，在距地面约10 cm处观测到的溶质浓度分布出现峰值。