浅层包气带水汽昼夜运移规律及其数值模拟研究

西北干旱、半干旱地区,浅层包气带水分通量主要由水汽组成,而水汽在运移过程中产生的能量转换和质量迁移是地表质能平衡计算不可缺少的重要源汇项。在野外进行一个沙坑实验,发现土壤水在中午(12:00—15:00)达到最大值(10cm深度,5.9~6.1cm3/cm3;30cm深度,11.9~13.1cm3/cm3),而在凌晨(02:00—05:00)出现最小值(10cm深度,4.4~4.5cm3/cm3;30cm深度,10.4~10.8cm3/cm3)。为进一步验证该实验条件下的土壤水运移及分布规律,考虑了土壤水、汽、热耦合运移的HYDRUS-1D模型被用来对实验过程进行模拟,模拟结果与实测结果吻合较好。为描述土壤水分昼夜运移模式,笔者将土壤水耦合运移的时间信息和空间信息进行同步分析;并根据土壤水运移的不同驱动力,分别对温度梯度、基质势梯度作用下的液态水及汽态水通量进行了分析。

The diurnal pattern of soil water fluxes in subsurface zone and its simulation analysis

In desert and semi-desert areas,vapor movement is often an important part of the total flux since it controls the partitioning of available energy into latent and sensible heat fluxes into the atmosphere.In addition,biological processes such as soil microbial activity and plant growth depend on the moisture and temperature status in the vadose zone,which are mainly influenced by the vapor movement.An experiment,in which the hourly measurements of water vapor flux in the vadose zone were reported,was conducted in a sand-filled bunker at a field site.It was found that the soil moisture reached the daily maximum value(5.9-6.1 cm3/cm3 at 10 cm and 11.9-13.1 cm3/cm3 at 30 cm)and minimum value(4.4-4.5 cm3/cm3 at 10 cm and 10.4-10.8 cm3/cm3 at 30 cm)at midday(12:00-13:00 for 10 cm and 14:00-15:00 for 30 cm)and before dawn(02:00-03:00 for 10 cm and 04:00-05:00 for 30 cm),respectively.The modified HYDRUS-1D code,which refers to the coupled water,vapor and heat transport in soil,was used to develop a deeper understanding of the physical processes of soil water dynamics in this experiment.The numerical analyses provided insight into the diurnal movement of liquid water and water vapor driven by the gradients of pressure heads and temperatures in the subsurface zone.The simulated temperature and water content were in good agreement with the measured values.The spatial-temporal distribution of liquid water flux,of water vapor flux and of soil temperature showed a detailed diurnal pattern of soil water dynamics in relatively coarse sand.