Investigating correlative & causal drivers of precipitation-driven groundwater recharge occurrences in southeastern Australia

Study region National Groundwater Recharge Observing System (NGROS) sites, Australia Study focus Identifying controls on groundwater recharge occurrences remains a central challenge in hydrology. Although broad consensus exists on key variables influencing recharge, there is less agreement on their relative importance and whether observed relationships are causal or merely correlative. Existing studies rely on approaches limited in capturing non-linear behavior or only capture single measures of association without addressing causal linkages. This study quantifies both correlative and causal relationships between key variables and potential groundwater recharge occurrences across nine NGROS sites. NGROS is the first dedicated sensor network to observe groundwater recharge at event scale in underground spaces across Australia. Using high-resolution drip monitoring data as direct indicators of recharge events, relationships between recharge occurrences and potential drivers, including precipitation, soil moisture, evapotranspiration (ET), and vegetation dynamics (NDVI), were quantified using both correlation-based and causality-oriented analyses, including first application of Convergent Cross Mapping (CCM) to identify causal linkages influencing recharge occurrences. New hydrological insights Results show that soil moisture and vegetation are the strongest predictors of recharge occurrences. ET shows moderate seasonal importance, particularly during austral autumn, but remains secondary overall. Although daily rainfall shows weak association, cumulative precipitation over 6–7 days shows stronger predictive association. Soil moisture also has longer response lags (> 3 weeks) compared to rainfall (7–10 days).