New groundwater recharge model for water table fluctuation method calibration using easily available data

Groundwater recharge is an essential input for groundwater resources management, yet it is not directly measurable. Here we present a new model for calibrating specific yield of unconfined aquifers, which improves the estimation of groundwater recharge using the water table fluctuation method. The new soil moisture deficit model of root zone (for shallow and deep rooting plants separately) was derived from existing bucket models. The model simulates water table levels in wells using easily available data, namely precipitation and air temperature. The specific yield was calibrated by comparing the modelled and observed water table. The observed water table and the calibrated specific yield are used in water table fluctuation method to determine groundwater recharge. The model was applied to 9 wells in the lowland along the river Labe (Czechia), for which decadal records of water table fluctuation are available. The obtained values of specific yield ranged from 5 % to 17 %, which is realistic for the studied fluvial aquifers with unconfined water table. The results were compared with an established model HYDRUS-1D, which yielded similar results. The obtained long-term mean groundwater recharge is in alignment with the outcomes of a previous study for the nearby sites. The proposed model provides a valuable tool for calibrating the specific yield, thus overcoming a major obstacle in determining groundwater recharge using the water table fluctuation method. Furthermore, the model can potentially be employed to estimate the impact of future climate characteristics on groundwater resources, as it can capture changes in vegetation patterns.