Time series analysis of synthetic time series generated with a saturated/unsaturated zone model

Time series analysis with response functions is a versatile approach to analyze measured head series in observation wells. In such an analysis, the response function of the groundwater does not change with time. This approach works well when the groundwater recharge is a linear function of the measured rainfall and evaporation, as was shown through the analysis of synthetic time series generated with a saturated groundwater model where the groundwater recharge is applied directly to the saturated zone. In this research, the method was evaluated for situations where the groundwater recharge cannot be approximated well as a linear function of the measured rainfall and evaporation. Synthetic time series were generated with a two-dimensional saturated/unsaturated zone model (Hydrus2D) and analyzed with response functions. Performance of the time series model was improved through inclusion of a new root zone model consisting of a single reservoir. Reservoir inflow is measured rainfall. Reservoir outflow is evaporation and groundwater recharge, where the evaporation is a function of the amount of water stored in the root zone and the recharge is a function of both the amount of water stored in the root zone and the groundwater table. The new root zone model is a promising tool for the analysis of head series in areas with thick unsaturated zones and/or high potential evaporative fluxes.