Numerical simulation of groundwater evaporation in the Badain Jaran Desert of China

To determine the relationship between groundwater evaporation and depth to the water table in the Badain Jaran Desert, 54 different scenarios are designed based on the climate background, the characteristics of aeolian sandy soils and the typical vegetaion types at different groundwater depths of the the desert, and the SPAC water transport models for each scenarios are established to numerically simulate the groundwater evaporation which are driven by the periodic meteorological conditions. The simulation results show that the annual average groundwater evaporation decreases non-linearly with the increasing depth to the water table. The extinction depths under different scenarios are greater than 3 m, and the groundwater evaporation is less than 5% of the maximum value when the water table is at a depth of 3 m. When the depth to the water table is 0.5-1.5 m, the groundwater evaporation is very sensitive to the change in the depth to the water table, and when the depth to the water table is 1 m, the groundwater evaporation is also sensitive to the lithology of the vadose zone. When the depth to the water table is beyond the scope of 0.5-1.5 m, the impact of the climate, lithology and depth to the water table on groundwater evaporation becomes weak. In addition, the nonlinear relationship between the annual average groundwater evaporation and the depth to the water table can be accurately fitted with a newly proposed empirical formula. The quantity of the groundwater evaporation in the lake concentration area of the Badain Jaran Desert is assessed based on the above fitting results. The evaluation results show that the total amount of the groundwater evaporation is significantly larger than that of the evaporation from the lake surface, and the former is 2.5-2.6 times as large as the latter, which must be considered in the analysis of the water balance.