Modeling soil moisture variations for direct groundwater recharge estimation in the critical zone

Abstract

<p>It is becoming increasingly important to develop simple and efficient models for the assessment of groundwater recharge to improve sustainable groundwater management strategies. Reliable data on environmental fluxes can be collected on-site and for corresponding periods, providing information on groundwater recharge only after measurement campaigns covering several years. However, the large amount of hydrological data necessary for some methods to estimate recharge is not always available. To address these issues, a specific model for the evaluation of vertical water fluxes in the critical zone was developed. The model is directly based on soil moisture sensor data in the critical zone and does not require modeling of meteorological processes, nor time series of precipitation, temperature, relative humidity, global radiation, or sunshine hours. Based on the numerical solution of the Richards equation and using Van Genuchten relationships for soil parameterization, percolation rates and subsequent groundwater recharge are derived from potential gradients and variations of volumetric soil moistures at different depths in the critical zone. Model results are evaluated with a detailed performance analysis with several mathematical error indices and graphical methods. The resulting fluxes have been validated with an independent stable isotope profile approach confirming the applicability of the model. The model can be applied to a soil moisture monitoring station with three monitoring sensors in the critical zone to derive daily time series of water fluxes.</p>