Estimating Shallow Groundwater Evaporation Based on Surface Evaporation and Ambient Air Temperature

Abstract

【Objective】 Evaporation loss via capillary rise is an important component of groundwater cycle but difficult to measure in situ. This paper presents an empirical formula to estimate it using surface evaporation and ambient air temperature, based on long-term experimental data obtained from a hydrological experimental station. 【Method】 Groundwater evaporation from phreatic surface of shallow groundwater was measured from lysimeters with cross section of 0.3 m2 at Wudaogou Hydrological Experiment Station, and the meteorological data were measured from a weather station installed at the station. There were two soils, a fluvo-aquic soil and a lime concretion black soil. For each soil, we established a regression model using temperature and surface evaporation, either separately or in combination, to estimate groundwater evaporation. 【Result】 For the lime concretion black soil, the average R2 of the models using single or two meteorological factors was 0.88, and its associated average absolute error (MAE) and root mean square error (RMSE) were 0.15 mm/d and 0.23 mm/d, respectively. For the yellow fluvo-aquic soil, the associated results were R2=0.92, MAE=0.194 mm, and RMSE=0.28 mm/d. When using a single meteorological factor, the average R2 for the two soils using all models was R2=0.92, and its associated MAE and RMSE were 0.18 mm/d and 0.26 mm/d, respectively. In contrast, in using the two meteorological factors, the average R2 for the two soils using all models was 0.94, and its associated MAE and RMSE were 0.14 mm/d and 0.205 mm/d, respectively. 【Conclusion】 For a given area, the evaporation of its shallow groundwater via capillary rise depends on surface evaporation and ambient air temperature. Since air temperature and surface evaporation are closely correlated, we can use either one of the two factor or their combination to estimate the groundwater evaporation.

Keywords

• shallow groundwater evaporation
• surface water evaporation
• air temperature
• groundwater depth