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

通过柱式蒸发试验和数值模拟，探讨了半干旱区蒸发与盐渍化的关系。一个长100厘米、直径10厘米的砂柱由西澳大利亚的沙质土壤制成，安装在天平上，通过排水过程，设置浅水位（案例A）或均匀分布的田间容量含水量剖面（案例B）。将其上表面暴露于控制在25℃和20%相对湿度的环境空气中，开始蒸发实验，在模拟太阳辐射时，在该表面施加550 W/m^2的热流通量。下面是公认的。沙粒快速溶解形成的土壤水的化学成分主要为Cl、Na^+、Mg^<2+>，且浓度较高。在靠近沙表面的区域，特别是在案例B中，干燥程度更高，盐碱化也更发达，其中蒸发区向下移动到2厘米深（对于案例a， 1厘米）。每一种情况下，在40天后，砂表面都形成了一层结皮，B的厚度为5 mm。据估计，蒸发产生的蒸汽在地壳中的向上输送阻力比在该锋面上相当干燥的地区大一个数量级。只有在加热的情况下，蒸汽才会向下运动。基于水分、水汽热和化学成分的垂直一维数值模型，改进了地表湍流输送体积系数、反照率和红外辐射发射率，较好地再现了中国西部半干旱区沙丘的水文气象资料。在那里观测到的溶质浓度分布特征可通过10年计算再现。

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.