The Effect of Precipitation Pulses on Evaporation of Deeply Buried Phreatic Water in Extra-Arid Areas

Past research has shown that evaporation of deeply buried phreatic water occurs in extra-arid areas where the soil surface is very dry. A dry surface layer can suppress the evaporation of capillary water, but it is not clear whether it suppresses deeply buried phreatic evaporation (PE). We deduced that the PE could be suppressed by a dry surface soil. Therefore, as the soil-water content increases during a precipitation pulse, this can lead to an increase in PE. To investigate the effects of precipitation pulses on PE, a simulated 10-mm precipitation recycling experiment using a shed-air-conditioning condensation method was performed on Gobi Desert land at the top of the Mogao Grottoes in 2011 to 2015. The results show that after the 10 mm of precipitation was completely recycled, the PE increased by 28.9% compared with the control during the following 3 yr. In addition, the soil moisture increased in the 10- to 20-cm layer for a long time. We hypothesize that this is a soil-water hysteresis phenomenon, which is important for the observed differences in the evaporation rate, and it is apparent that the higher water content in the shallow layer is conducive to PE entering into the atmosphere. This preliminary study reveals the effect of precipitation pulses on deeply buried PE; this hysteresis phenomenon must be analyzed in further studies.