Submitted to: Hydrological Sciences Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2011
Publication Date: 8/1/2011
Citation: Guber, A.K., Gish, T.J., Pachepsky, Y.A., Mckee, L.G., Nicholson, T., Cady, R. 2011. Event-based estimation of water budget componets using the network of multi-sensor capacitance probes. Hydrological Sciences Journal. 56:1227-1241. Interpretive Summary: Soil water budgets, consisting of inputs from runoff, infiltration, and evapotranspiration, provide essential information to estimate groundwater recharge and transport of pollutants to groundwater and surface water. Current methods for estimating soil water budgets are inadequate due to the absence of objective methods to select the proper time interval over which the budget is computed. It has previously been shown that the selection of different time intervals can substantially impact estimates of groundwater recharge. We propose a time-scale-free approach to soil water budget computations based on the availability of multi-sensor soil water probes that provide accurate data on soil water content. Based on this information, it is fairly easy to distinguish between rainfall events that result in an increase in soil water content from infiltration vs. intervening drought events that result in a decrease in soil water content from evaporation and leaching to sediments below the soil. The duration of these events serves as the budget time interval. This approach was tested with data from the USDA-ARS OPE3 site in Beltsville, and resulted in reasonable estimates of soil water budgets as well as the uncertainty caused by spatial variation in soil properties. This work provides a reliable method of estimating soil water budgets based on commercially available modern multi-sensor soil water probes. The results of this work are important for soil scientists, hydrologists, environmental engineers, and agronomists concerned with soil water budgets and groundwater resources nationwide.
Technical Abstract: A time-scale-free approach was developed for estimation of water fluxes at boundaries of monitoring soil profile using water content time series. The approach uses the soil water budget to compute soil water budget components, i.e. surface-water excess (Sw), infiltration less evapotranspiration (I-ET) and groundwater recharge (R) for time intervals between two sequential minima on the soil water storage time series. The approach was applied for water contents time series measured from May 1, 2001 through January 1, 2003 at 8 locations in a 3.6 ha field located at the USDA, Beltsville Agricultural Research Center, Beltsville, Maryland. The soil water budget components were normalized by rainfall amounts over recharge events to estimate precipitation partitioning between surface-water excess and infiltration, and rainfall contribution into the groundwater recharge. High uncertainty obtained for the precipitation partitioning was attributed to spatial and temporal variability in Sw, I-ET and R, and caused by nonuniform rainfall distributions over events, variability in the profile water content distribution at similar soil water storage values, and spatial variability in soil hydraulic properties. Overall, the proposed event-based approach appeared to be appropriate for estimating uncertainty in water budget components when profile water content monitoring data were available.