Relationships between evaporation-precipitation and salinization in a semi-arid area

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A relation between evaporation and salinization in a semi-arid area was explored through a column evaporation experiment and a numerical simulation.A sand column 100 cm long and 10 cm in diameter made using a sandy soil in Western Australia was installed on a balance, where via a draining process, a shallow water table (Case A) or a uniformly distributed water content profile in field capacity (Case B) was set. By exposing Its upper surface to ambient air controlled at 25℃and 20 % of RH, the evaporation experiment was started, where, when a solar radiation was simulated, a heat flux at 550 W/m^2 was applied on that surface. The following was recognized. Chemistry of soil-water formed through a rapid dissolution of sand particles was mainly Cl, Na^+, Mg^<2+> and showed a high concentration. Dryness in a zone near the sand surface, in particular, for Case B was more advanced and salinization was also much more developed, where the evaporation zone moved down to 2 cm deep (for Case A, 1 cm). For every case a crust was formed on the sand surface and its thickness for Case B was 5 mm after 40 days. Upward transport resistance for vapor generated by evaporation was estimated one-order of magnitude larger in the crust than that in fairly dried zone overlying that front. Only in the case that heat was applied, a downward movement of vapor appeared.Based on a vertically one-dimensional numerical model on moisture, vapor heat and a chemical component, the hydro-meteorological data observed over a sand dune in semi-arid area in Western China (HEIFE) were reproduced well after improvement on bulk coefficients of turbulent transport from surface, albedo and emissivity of infrared radiation. A characteristic of solute concentration profile observed there could be reproduced by 10-year calculation.