Estimation of groundwater evapotranspiration rate in the loess phreaticaquifer by removing the barometric effect

Groundwater evapotranspiration (ET_g) is the most important dischargeway of shallow groundwater in arid and semi-arid areas, and also is a significant component of the water budget in groundwater systems. When groundwater levelsare interfered with barometric effect, the traditional water table fluctuation method for estimation of the ET_g rate cannot be directly employed.This paper proposes a hydrographical method for removing the barometric effect on the ET_g rateestimation using water-table fluctuations based on the changes ingroundwater levels and barometric pressure.The results illustrate that thechangesin barometric pressure usually reach the peak before midnight, generally between 22:00 and 24:00 when the barometric effect can be ignored, and the evapotranspiration rate is the minimum and therefore thegroundwater level changes rate at this time interval is equivalent to the net recharge rate. Furthermore, the second time period between 0:00 and 4:00 when the ET_g rate is negligible and the barometric pressure is generally in a continuous decline, is then selected to estimate the barometric efficiency. On the basis of these analyses, the ET_g rate can be readily estimated by the groundwater level balance method and the water table fluctuation method. The data required in theproposed methodare easy to obtain and the estimated ET_g ratesare relatively accurate.