Seasonality in groundwater recharge - Observational evaluation of Earth System model realism

Despite many efforts to estimate both the spatial and temporal dynamics of groundwater recharge, and to predict how these will be altered by climate change, this crucial part of the water balance remains highly uncertain. Meanwhile, many shallow aquifers are experiencing alarming water level declines due to a combination of high anthropogenic withdrawals and altered precipitation patterns. This work combines recent and long-term datasets from locations throughout the continent of Australia to re-examine how shallow recharge dynamics vary across a diversity of climate types. Available data from a drip logger network demonstrate the interannual variability in rainfall recharge thresholds, with seasonality in the number of recharge events and the rainfall recharge threshold. Historical records of rainfall are then examined to understand the historical return interval of these rainfall volumes, both annually and seasonally. Finally, we examine our results against corresponding data in the historical model runs from the Coupled Model Intercomparison Project (CMIP), to evaluate the realism of the models. The results of this combined methodology provide a more nuanced approach to evaluating the resilience of groundwater supplies in a changing climate.