Reconciling surface and groundwater models in a climate change context

Abstract

To understand the possible impacts of changes in rainfall and potential evapotranspiration (PET) in a river catchment in which surface water and groundwater systems are connected, the dynamic interaction that exists between changes in surface runoff, groundwater recharge, and groundwater levels must be represented appropriately. While such a system can be modelled using fully coupled groundwater-surface water flow models, it is more common for separate specialised models to be developed independently by different teams for different purposes. The assumptions, parameters and outputs of the models are not compared. This paper develops a methodology for comparing specialist hydrological models commonly used in Australia to simulate catchment processes. Three models were developed, initially independently, of the Cox Creek sub-catchment in the Mount Lofty Ranges of South Australia: a LEACHM model of groundwater recharge, a SOURCE model of surface water runoff, and a MODFLOW model of groundwater flow. The models are reconciled by using multiple outputs of the LEACHM model as inputs to the MODFLOW model, and calibrating the MODFLOW model to SOURCE outputs. Reconciliation of the inputs and outputs of the three models with each other should improve the rigour in each model's simulation of catchment processes. The reconciled models will be run with stochastically-generated input data sets of rainfall and PET, representing a variety of possible future climate scenarios generated by one of the CMIP5 group of global climate models. Reconciled outputs of the three models are expected to reveal some of the complexities in the inter-related responses of groundwater and surface water flow systems to multi-decadal timescale changes in rainfall patterns.