Groundwater storage changes using GRACE and ESA CCI soil moisture products in Southern Victoria, Australia

Abstract

Groundwater depletion, driven by climate change and increasing extraction for irrigation, has increased the need for accurate monitoring. Traditional methods, such as in situ water table observations and pumping tests, are valuable for assessing groundwater availability and aquifer characteristics but are limited in capturing basin-scale variations. The Gravity Recovery and Climate Experiment (GRACE) enables estimation of basin-scale groundwater changes, though its observations also include surface water and soil moisture (SM) in the vadose zone. Therefore, additional data on non-groundwater components are needed to isolate groundwater variations. In this study, we use the profile SM content for the top 0–120 cm of soil as an estimate of vadose zone SM, derived using an exponential filtering technique applied to European Space Agency's Climate Change Initiative for Soil Moisture (ESA CCI SM) and in situ data. This approach addresses limitations of conventional models, such as their inability to represent non-natural or lateral water redistribution. Groundwater storage (GWS) changes in southern Victoria, Australia were estimated by subtracting the filtered SM from GRACE data and validated against in situ groundwater level observations for both unconfined and confined aquifers. The ESA CCI SM-based estimates showed clear improvements in capturing seasonal and interannual variability of in situ GWS compared to conventional model-based estimates. The proposed approach is potentially applicable to GWS estimation at continental scales.