A hydrographic method to identify the groundwater net recharge, barometric effect and evapotranspiration from a complicated semidiurnal water table fluctuation

Abstract

AbstractA hydrographic method was proposed to separate out the hourly scaled groundwater level changes caused by net recharge, barometric effects and evapotranspiration from a semidiurnal water table fluctuation. A characteristic midnight time, with a turning point of the barometric pressure change and high relative air humidity, which meant that neither the barometric effect nor groundwater evapotranspiration occurred, was proposed for determining the net recharge rate rnet. Then, the barometric efficiency fbar was estimated using the other time period without evapotranspiration, and the evapotranspiration rate rETG was finally obtained using the remainder of the water level changes. A case example illustrated that estimation of fbar using the proposed method was more accurate than that using the traditional error analysis method, which may result in a significant underestimation under the condition of the present water level changes. Additionally, the abnormal semidiurnal fluctuations, more specifically, two step‐down fluctuations, which may be a common pattern when the groundwater level is controlled by net recharge, barometric effects and evapotranspiration, can be well understood using the three components separated out. The results also showed that nighttime groundwater evapotranspiration, accounting for an average of 23% of that during the daytime, cannot be ignored.