Rainfall recharge thresholds revisited: where and when is water getting underground?

Abstract
Groundwater recharge is central to sustainable water management, yet its timing and magnitude are difficult to determine. Since 2022, the National Groundwater Recharge Observing Network has been recording drip‑water logger data at an increasing number of sites across Australia to directly capture water flux through the unsaturated zone. Annual recharge thresholds range from 13 to 50 mm (average 23 mm) within 48 hours; differences between sites are not statistically significant. A clear seasonality emerges, however: at winter‑rainfall‑dominated locations, recharge occurred only in winter/spring, even though summer/autumn rainfall events exceeded the threshold. The findings are discussed in the context of common groundwater modelling and with consideration of climate change.

Short bio
Dr. Margaret Shanafield is an Associate Professor at the National Centre for Groundwater Research and Training (Flinders University). Her research combines field and modelling approaches to surface‑water and groundwater processes. From 2021 to 2024, she was a scientist at the Environmental Defenders Office (the largest public‑interest environmental law organization in the Southern Hemisphere). In 2025/26, she is an Alexander von Humboldt Visiting Scientist at the University of Potsdam and at the Potsdam Institute for Climate Impact Research, focusing on climate influences on water resources.