Groundwater δ2H/δ18O isoscapes for New South Wales (Australia)

New South Wales (NSW), Australia. Stable isotope ratios of water (δ 2 H and δ 18 O) can be used to trace hydrological processes, providing information on aquifer dynamics including groundwater recharge, flow and mixing. We combine new and pre-existing isotope data to produce the first groundwater stable isotope maps (“isoscapes”) across NSW. Two-dimensional ordinary kriging is employed separately over four depth intervals to interpolate isotope values. The isoscape reveals key water sources such as floods or snowmelt in groundwater recharge as well as the impact of aridity towards the west of the state. Groundwater sources can be traced along all major alluvial valleys from shallow to deep layers across NSW. Regionally, shallow current groundwater isotopic signatures differ from those recharged before European settlement in the deeper layers. Land-use change has likely enhanced evaporative processes, with groundwater abstraction and irrigation accelerating groundwater recharge locally. This work shows that isoscapes are a powerful visual tool for interpreting changes in groundwater recharge sources and processes. They can also be used as a predictive tool at data-poor locations or to enhance local groundwater management decision in areas with large data coverage. As isoscapes become more data-rich and sophisticated, and incorporate hydrogeological models, they will continue to improve regional to continental-scale groundwater characterisation contribution to sustaining ecosystems, agriculture, and human populations. • First depth-layered groundwater stable isotope map of New South Wales (Australia). • Large-scale groundwater recharge and near-surface processes revealed. • Lower groundwater δ 18 O and δ 2 H with depth show dynamic changes in time. • Groundwater management-zone interpretations possible at higher resolution.