Canada’s water resources are critical for communities, ecosystems, and industry, yet quantifying changes in land water storage – whether as snow, soil moisture, surface water, or groundwater – remains challenging at national scales. As part of the Canada 1 Water project, this study demonstrates that combining satellite gravity observations from the GRACE and GRACE FO missions with HydroGeoSphere (Aquanty), a fully coupled surface water – groundwater model, provides a robust framework for monitoring and interpreting terrestrial water storage change across Canada.

We examine water storage variability across a range of hydroclimatic and physiographic settings, including Southern Ontario, the Great Lakes Basin, the South Saskatchewan River Basin, the Nelson Basin, and the Mackenzie Basin. Across these regions, satellite and model-based estimates show strong agreement in both the timing and magnitude of seasonal and longer term water storage variations, demonstrating that GRACE can resolve meaningful regional scale changes even near its spatial resolution limit. The results highlight coherent seasonal cycles, interannual variability, and longer term trends in land water storage that reflect the integrated response of surface and subsurface hydrological processes.

By synthesizing satellite gravimetry with advanced, physics based hydrological modeling, this work provides an observation constrained view of water storage change across Canada’s major basins. Such integrated approaches are essential for improving drought monitoring, understanding hydrological responses to climate variability and change, and supporting climate adaptation and sustainable water resource management at both regional and national scales.