Top-down groundwater hydrograph time-series modeling for climate-pumping decomposition

Groundwater time-series modeling has emerged as an efficient approach for simulating the impacts of multiple drivers of groundwater-head variation such as rainfall, evaporation and groundwater pumping. However, a bottom-up approach has generally been adopted whereby the input drivers have been assumed without statistical evidence for their inclusion. In this study, a parsimonious time-series model was adopted which accounts for various drivers and is able to simulate the overall groundwater-head variation. It can also separate the effects of pumping and climate drivers on multi-annual time series of groundwater-level variation. The time-series model consists of a soil-moisture layer to account for non-linearity between rainfall and recharge, as well as different pumping response functions to account for pumping from a single well, lake-induced recharge and the effects of multiple pumping bores. The method was applied to a groundwater-pumping region in south-eastern Australia. The results showed that the model is able to separate the effects of pumping from the effects of climate on groundwater-head variation. However, improved estimation of those influences requires a flexible model structure that can account for spatially varying physical processes within the study region such as the relative influence of single or multiple pumping bores and induced recharge from surface-water bodies.