Depth-Dependent Seasonal Variation of Soil Water in a Thick Vadose Zone in the Badain Jaran Desert, China

In a vadose zone the soil water content can change seasonally, driven by seasonal variations of meteorological factors. This dynamic behavior is depth-dependent, which controls the groundwater recharge from infiltration, and plays an essential role in the environments in arid and semi-arid regions. In particular, the depth-dependent seasonal variations of soil water were investigated in the Badain Jaran Desert (BJD), China, where the vadose zone is thick. The monitoring results showed that the amplitudes of temperature and soil moisture content in the shallow vadose zone (depth < 3 m) significantly decrease with depth. For the deep vadose zone (depth >3 m), the depth-dependent dynamic was synthetically estimated with both numerical and analytical models. Results show that the penetration depth of seasonal fluctuation is about 47 m, below which the infiltration flux stabilizes at a level of 30.7 ± 4 mm/yr. The depth to water table in the BJD is generally larger than 50 m, up to 480 m. As a consequence, groundwater recharge from infiltration in this area almost does not change in different seasons.