Prediction of long-term groundwater recharge by using hydropedotransfer functions

The investigations to estimate groundwater recharge were performed. Improved consideration of soil hydrologic processes yielded a convenient method to predict actual evapotranspiration and hence, groundwater recharge from easily available data. For that purpose a comprehensive data base was needed, which was created by the simulation modelSWAPcomprising 135 different site conditions and 30 simulation years each. Based upon simulated values of actual evapotranspiration, a transfer function was developed employing the parameter b in the Bagrov differential equation dEa/dP = 1- (Ea/Ep)b. Under humid conditions, the Bagrov method predicted long-term averages of actual evapotranspiration and groundwater recharge with a standard error of 15 mm year-1 (R = 0.96). Under dry climatic conditions and groundwater influence, simulated actual evapotranspiration may exceed precipitation. Since the Bagrov equation is not valid under conditions like these, a statistic-based transfer function was developed predicting groundwater recharge including groundwater depletion with a standard error of 26mm(R = 0.975). The software necessary to perform calculations is provided online.