Groundwater net discharge rates estimated from lake level change in Badain Jaran Desert, Northwest China

Over a hundred sizable lakes, some even larger than ~1 km 2 , are distributed across the lowlands between megadunes in the southeastern Badain Jaran Desert (BJD), northwest China. With rather limited precipitation and hardly any surface runoff, these lakes are fed mainly by groundwater. However, the source of the groundwater and the groundwater discharge rates to these lakes are poorly understood. Water level and temperature of four representative lakes in the southeastern BJD were monitored continuously between 2013 and 2017. Water surface evaporation and rainfall in this area were also measured. Combining these acquired data, groundwater discharge rates were estimated using water balance models. The results show that the four lakes have similar recharge and discharge patterns, but at different average net groundwater discharge rates ranging from 1.79 to 3.09 mm d −1 . The lake level variation mainly depends on groundwater discharge and lake surface evaporation. We found that diurnal lake level variation may be controlled by earth tide and atmospheric pressure change, and is five times greater than the evaporation. The desert precipitation and deep confined groundwater with high temperature were found also recharging the desert lakes. An Empirical Mode Decomposition (EMD) method was used to identify the lake level trend. All lake levels increased over the last four years, except one decreased in 2015 and 2016. The lake levels’ increasing trend is synchronously similar with the precipitation in north China. This study analyzes annual and seasonal lake level variations, and also finds the diurnal water cycle between the groundwater and lake water for the first time.