Observational Research on the Relation between Evaporation, Precipitation and Salinization in a Semi-Arid Area in Western Australia

为了探讨西澳大利亚半干旱地区蒸发与盐碱化的关系，CSIRO位于贝克斯山的Yalanbee实验场于2000年10月至2003年3月进行了水文和气象观测。此外，作为密集的观测，有时通过直接采样来检查土壤水分和化学浓度的剖面，并通过穹顶蒸发实验测量土壤中的水蒸气密度和地面水汽通量来评估蒸发速率。在雨季(年降雨量：400 mm)，降雨入渗和地下水位上升降低了盐碱化程度，但其浓度与海水的浓度相当。土壤-水的主要离子为Cl、Na~+和Mg~(2+)~(2+)。在地表附近观察到的溶质浓度，如Cl-，对那里的特定水分含量有一个上限。对于质量湿度(M)小于0.12的区域，这一界限是恒定的(饱和值)，而对于质量湿度(M&GT；)为0.12的区域，该值呈指数下降。夏季，土壤中的水汽密度在小于5 cm的浅层随深度线性增加，但其斜率在地表周围不连续变化。这可能是由于地壳的阻力大得多造成的。利用VAISALA MAWS 101和201进行连续两年的天气观测，得到的连续两年的水汽通量与圆顶实验的水汽通量基本一致，可以用来估算蒸发量和热量。研究发现，太阳辐射在地表的反射(反照率)随季节变化而变化，盐碱化通过反照率的变化影响热量平衡。

In order to explore the relation between evaporation and salinization in semi-arid areas in Western Australia, in CSIRO's Yalanbee experimental site in Bakers Hill, hydrological and meteorological observations were undertaken from October 2000 to March 2003. Also, as intensive observations, profiles of soil-water content and chemical concentration were sometimes examined via a direct soil sampling, and to evaluate evaporation rate, measurements of water vapor density in soil and vapor flux at the ground via a dome evaporation experiment were undertaken.Salinization was markedly advanced in dry season and salt crust 5mm thick was formed on the ground surface. In wet season (annual rainfall : 400 mm), degree of that salinization was lowered by rain-infiltration and rising of water-table but its concentration was the same order of magnitude as the sea-water. Dominant ions of soil-water were Cl, Na^+ and Mg^<2+>. Solute concentration such as Cl- observed near ground surface showed an upper bound against a specific water content there. That bound is constant (saturated value) for mass wetness (M) less than 0.12, while for M>0.12, the value decreased exponentially.In summer, vapor density in soil was detected to increase linearly with depth in a zone shallower than 5 cm but its slope changed discontinuously around the ground surface. This may be caused by a significantly larger resistance of the crust. Vapor flux calculated using that linear line was more or less consistent with that through the dome experiment.Continuous data for two years obtained through the weather observation using VAISALA MAWS 101 and 201, could be applied to estimation of heat budge and evaporation. It was found that reflection (albedo) of solar radiation on the ground surface varied seasonally and the salinization affected the heat balance via the variation in the albedo.