Study on Influences of Salinization on the Evaporation Processes in a Semi-arid Area in Western Australia

为了阐明地表蒸发与盐碱化之间的关系，从2000年开始，在西澳大利亚州半干旱地区（Yalanbee）的裸露土壤区进行了为期三年的气象和水文观测。本研究通过对所得数据的分析和辅助蒸发实验等，对这一关系进行了探讨。结果表明：（1）在野外，盐结皮主要是由夏季（旱季）蒸发作用形成的;冬季（湿季）土壤被降雨事件湿润。然而，旱季的地面反射率（太阳辐射的反射率）比雨季小10%。这种反向关系不能通过使用雅兰蜂土的实验来识别，并且仍然是未来的问题。(2)在旱季，野外反照率随太阳高度的增加而减小，但其最小值不是出现在中午，而是出现在上午10点左右，这被认为是 ...更多信息 由于土壤湿度的减少通常会使土壤湿度增加，因此蒸发使地表干燥。这种情况对应于圆顶蒸发实验的结果，即蒸发率从上午10点左右突然下降，由于太阳辐射的增加，蒸发率从日出开始连续增加。(3)在干旱季节，大气温湿度和太阳辐射的日变化引起土壤中的蒸发-凝结。通过在类似于这些实际变化的气象条件下进行的实验室雅兰蜂土柱实验，阐明了当土壤层中的蒸汽运动由扩散方程描述时，其修正的扩散系数变得比原始扩散系数大约100倍。（4）在地下水位较浅的土柱蒸发试验中，盐结皮在土壤表层不均匀地形成，其发展速度很快，约占结皮面积的60在实验开始后的大约五天内。蒸发速率随结皮面积的减小而线性减小，有效可输送截面的减小导致蒸发通量和蒸发速率显著减小。少

In order to clarify the relation between evaporation from the ground surface and salinization, a meteorological and hydrological observation was undertaken in a bare soil area in a semi-arid region (Yalanbee), Western Australia for three years from 2000. In this research, through analysis on that obtained data and a subsidiary evaporation experiment so on, that relation was investigated. The following was disclosed:(1) In the field, salty crust is formed by occurrence of evaporation in summer (dry season) and in. winter (wet season) soil is wetted by rainfall events. However albedo (reflection rate of solar radiation on the ground) in the dry season becomes by 10% smaller than that in the wet season. This reverse relation could not be recognized through an experiment using Yalanbee-soil and still remains as a future problem.(2) Albedo in the field in the dry season decreases with solar altitude, but its minimum was detected to appear not at noon but around 10 a.m. This is considered to … More be due to drying of ground surface by evaporation because reduction of soil wetness usually lets the albedo increase. This situation corresponds to such a result by a dome evaporation experiment that evaporation rate decreases abruptly from around 10 a.m. via its continuous increase from sunrise due to increasing solar radiation.(3) In the dry season, daily changes in atmospheric temperature-humidity and solar radiation cause the evaporation -condensation in the soil. Through a laboratory Yalanbee-soil column experiment under a meteorological condition similar to these actual variations, it was clarified that, when vapor movement in the soil layer is described by a diffusion equation, its modified diffusion coefficient becomes approximately 100 times larger than the original one. This increase is concluded to be caused by occurrences of evaporation and condensation, and structure and behavior of the modified coefficient were also clarified theoretically(4) In an evaporation experiment using the soil column with a shallow water-table, salty crust was observed to be formed non-uniformly on the upper soil surface and its development was very fast as the crust area became about 60% within about five days from the beginning of experiment. Also it was recognized that the evaporation rate decreased linearly with inverse of the crust area, and reduction in effective transferable cross-section for vapor leads to the decrease in vapor flux, evaporation rate, significantly. Less