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

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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.