ON THE ROLE OF INTEGRATED GROUNDWATER-LAND SURFACE MODELS FOR GROUNDWATER SUSTAINABILITY ASSESSMENTS (Invited Presentation)

The importance of groundwater resources as a resilient water supply has been increased in recent years, and efforts are underway to achieve groundwater sustainability and reduce overdrafts in various regions. However, the concept of groundwater sustainability is broad and includes groundwater management without causing undesirable environmental, economic, or social impacts. As a result, sustainable groundwater management and quantifying capture should consider a range of factors including surface water and groundwater dependent ecosystems. Recently, a number of physically based integrated hydrologic models are developed to simulate terrestrial hydrologic processes from atmosphere to the land surface and subsurface. Despite the complex structure of integrated hydrologic models, predictions suffer from the same elements of uncertainty in hydrologic modeling. Of particular importance is the consideration of uncertainty in model initialization, and assessing its impact on model predictions. In this study, an integrated groundwater-surface water-land surface model (ParFlow.CLM) was set-up over the 208 km² Ringkobing Fjord catchment in Denmark. Various measures of spin up performance were computed for model state variables such as soil moisture and groundwater storage, and discharge and latent heat flux. Results illustrate that equilibrium in subsurface storage ensures equilibrium across a range of other variables. In addition, improper initialization of the model affects subsequent simulations and leads to misinterpretation of land surface-subsurface feedback processes. To reduce the computational time of the spin-up process, a new hybrid spin-up approach is introduced which reduces computational time by 50% in two catchments located in Denmark and Australia. Although, integrated hydrologic models provide valuable information for sustainable groundwater management across multiple processes and scales, certain care should be considered in their implementation.