Terrestrial Water Storage (TWS) observed by GRACE and GRACE Follow-On contribute to the Global Water Monitor by underscoring extremes and trends observed in individual compartments of the water cycle and by identifying and emphasizing critical hotspots and large-scale phenomena.
Albert van Dijk, Australian National University, & Julian Haas, GFZ
In 2024, the world’s water systems were pushed to the limit. From deadly floods to crushing droughts, water-related disasters displaced more than 40 million people, cost over half a trillion US dollars, and left ecosystems—like the Amazon rainforest—badly scarred. These weren’t isolated incidents. They were part of a growing trend of water extremes driven by climate change. Those are some of the findings documented in the Global Water Monitor 2024 Summary report.
At the Global Water Monitor Consortium, we combine satellite and ground data to track the planet’s water in near-real time. Our latest report captures the hydrological state of the world in 2024 — one of extremes and contrasts. Global land temperatures were the highest ever recorded. Daily rainfall extremes occurred 52% more often than during the late 1990s. Droughts in Southern Africa halved crop yields, while floods in West and Central Africa reached record highs.
Among the powerful satellite-based tools are the GRACE and GRACE Follow-On satellite missions, which measure tiny variations in Earth’s gravity to estimate changes in water stored underground and across the landscape. These missions allow us to observe terrestrial water storage (TWS)—the sum of water in soil, groundwater, surface water, snow, and ice.
In 2024, TWS data showed worrying declines in many of the world’s drier regions. South America experienced its fifth consecutive year of declining lake and reservoir levels, while groundwater continued to deplete in key agricultural zones. In contrast, TWS increased in parts of Africa, reflecting the influence of wetter monsoon seasons.
Our monitoring integrates GRACE-based TWS estimates from the GFZ RL06v2 dataset, which we supplement using statistical interpolation to fill occasional gaps in satellite observations. This gap-filling approach ensures a continuous and reliable monthly time series, even during months when satellite measurements are unavailable or too uncertain. The result is a more robust and complete picture of long-term water storage changes.
The TWS data give us clarity on where water is accumulating or disappearing. For example, they help distinguish between surface flooding and long-term groundwater depletion, which is essential for water management and disaster preparedness.
As the climate warms, the risks to water supplies, infrastructure and communities grow. GRACE and GRACE-FO data help ensure that we are not flying blind. Together with the broader suite of satellite and ground observations, they offer a way to monitor our water future as it unfolds and to plan our responses to it.
You can explore our findings and data tools at www.globalwater.online.
References
2024 Report: Van Dijk, A.I.J.M., H.E. Beck, E. Boergens, R.A.M. de Jeu, W.A. Dorigo, C. Edirisinghe, E. Forootan, E. Guo, A. Güntner, J. Hou, N. Mehrnegar, S. Mo, W. Preimesberger, J. Rahman, P. Rozas Larraondo (2025) Global Water Monitor 2024, Summary Report.
2023 Report: Van Dijk, A.I.J.M., H.E. Beck, E. Boergens, R.A.M. de Jeu, W.A. Dorigo, T. Frederikse, A. Güntner, J. Haas, J. Hou, W. Preimesberger, J Rahman, P.R. Rozas Larraondo, R. van der Schalie (2024) Global Water Monitor 2023, Summary Report.