Leakage and evapotranspiration act as two major water losses for the largest lake on North China Plain during water diversion period

Artificial water diversion across watersheds is of great significance for the wetland restoration and groundwater water recovery in over-exploitation regions. However, if the local water cycling processes and balance remains unclear, it will in turn hinder effective water utilization and management. Surface water leakage concurs with groundwater overexploitation at the largest shallow grassy lake in the North China Plain, i.e., Baiyangdian Lake (BYDL). Simultaneously, evapotranspiration of the lake is another major factor causing water loss due to the widely distributed reeds. Since the establishment of Xiong’an New Area around BYDL in 2017, the lake water has been regularly replenished by artificial water diversion projects in autumn and winter, maintaining the year-round lake water level between 6.5 and 7.5 m. Many prior studies have measured the leakage or evapotranspiration in BYDL, but none of them has measured and compared both the leakage and evapotranspiration simultaneously. This study aims to better understand the contribution of these two aspects to lake water losses. The water level or hydraulic head, temperature of both the lake water and groundwater at different depths, and evapotranspiration rate were observed from August, 2019 to February, 2020, covered by the artificial water diversion. Using heat tracer method and eddy covariance technique, the lake leakage and evapotranspiration rates were evaluated and compared. It is found that during the monitoring period the average leakage rate (5.60 mm days −1 ) is more than twice of that (2.46 mm days −1 ) of the evapotranspiration. Furthermore, the lake water loss volume by leakage notably exceeded the average total lake capacity, which can be mostly attributed to the severe groundwater overexploitation in the underlying plain. These new findings will promote more accurate water diversion amount settings, groundwater recharge and wetland recovery assessments.