Satellite observations indicate a worrying decline in global freshwater levels starting from 2014, influenced by severe droughts and exacerbated by climate change.
The drop in water availability has critical implications for agriculture, health, and regional stability, with researchers highlighting the ongoing challenges in managing water resources effectively.
Startling Decline in Global Freshwater Reserves
An international team of scientists, using data from NASA-German satellites, has found evidence of a significant drop in Earth’s freshwater levels starting in May 2014. This abrupt decline has persisted, leading researchers to suggest that the planet’s continents may have entered a prolonged drier phase. The findings were published in Surveys in Geophysics.
Between 2015 and 2023, satellite measurements revealed that the average amount of freshwater stored on land—including surface water in lakes and rivers as well as underground aquifers—was 290 cubic miles (1,200 cubic kilometers) lower than the average recorded from 2002 to 2014. “That’s two and a half times the volume of Lake Erie lost,” explained Matthew Rodell, a hydrologist at NASA’s Goddard Space Flight Center and one of the study’s authors.
Impact of Drought and Agricultural Demands on Water Supply
During times of drought, along with the modern expansion of irrigated agriculture, farms and cities must rely more heavily on groundwater, which can lead to a cycle of declining underground water supplies: Freshwater supplies become depleted, rain and snow fail to replenish them, and more groundwater is pumped. The reduction in available water puts a strain on farmers and communities, potentially leading to famine, conflicts, poverty, and an increased risk of disease when people turn to contaminated water sources, according to a UN report on water stress published in 2024.
The team of researchers identified this abrupt, global decrease in freshwater using observations from the Gravity Recovery and Climate Experiment (GRACE) satellites, operated by the German Aerospace Center, German Research Centre for Geosciences, and NASA. GRACE satellites measure fluctuations in Earth’s gravity on monthly scales that reveal changes in the mass of water on and under the ground. The original GRACE satellites flew from March 2002 to October 2017. The successor GRACE–Follow On (GRACE–FO) satellites launched in May 2018.
Persistent Droughts and Their Global Consequences
The decline in global freshwater reported in the study began with a massive drought in northern and central Brazil, and was followed shortly by a series of major droughts in Australasia, South America, North America, Europe, and Africa. Warmer ocean temperatures in the tropical Pacific from late 2014 into 2016, culminating in one of the most significant El Niño events since 1950, led to shifts in atmospheric jet streams that altered weather and rainfall patterns around the world. However, even after El Niño subsided, global freshwater failed to rebound. In fact, Rodell and team report that 13 of the world’s 30 most intense droughts observed by GRACE occurred since January 2015. Rodell and colleagues suspect that global warming might be contributing to the enduring freshwater depletion.
Global warming leads the atmosphere to hold more water vapor, which results in more extreme precipitation, said NASA Goddard meteorologist Michael Bosilovich. While total annual rain and snowfall levels may not change dramatically, long periods between intense precipitation events allow the soil to dry and become more compact. That decreases the amount of water the ground can absorb when it does rain.
Challenges in Addressing the Water Crisis
“The problem when you have extreme precipitation,” Bosilovich said, “is the water ends up running off,” instead of soaking in and replenishing groundwater stores. Globally, freshwater levels have stayed consistently low since the 2014-2016 El Niño, while more water remains trapped in the atmosphere as water vapor. “Warming temperatures increase both the evaporation of water from the surface to the atmosphere, and the water-holding capacity of the atmosphere, increasing the frequency and intensity of drought conditions,” he noted.
While there are reasons to suspect that the abrupt drop in freshwater is largely due to global warming, it can be difficult to definitively link the two, said Susanna Werth, a hydrologist and remote sensing scientist at Virginia Tech, who was not affiliated with the study. “There are uncertainties in climate predictions,” Werth said. “Measurements and models always come with errors.”
It remains to be seen whether global freshwater will rebound to pre-2015 values, hold steady, or resume its decline. Considering that the nine warmest years in the modern temperature record coincided with the abrupt freshwater decline, Rodell said, “We don’t think this is a coincidence, and it could be a harbinger of what’s to come.”
Reference: “An Abrupt Decline in Global Terrestrial Water Storage and Its Relationship with Sea Level Change” by Matthew Rodell, Anne Barnoud, Franklin R. Robertson, Richard P. Allan, Ashley Bellas-Manley, Michael G. Bosilovich, Don Chambers, Felix Landerer, Bryant Loomis, R. Steven Nerem, Mary Michael O’Neill, David Wiese and Sonia I. Seneviratne, 4 November 2024, Surveys in Geophysics.
DOI: 10.1007/s10712-024-09860-w
More About GRACE-FO
The GRACE-FO (Gravity Recovery and Climate Experiment–Follow-On) mission is a collaboration between NASA and the German Research Centre for Geosciences (GFZ). It continues the groundbreaking work of the original GRACE mission (2002–2017), which was a partnership between NASA and the German Aerospace Center (DLR). Both missions use advanced satellite technology to measure changes in Earth’s gravity field, providing critical data on variations in mass, such as shifting water and ice.
The Jet Propulsion Laboratory (JPL), managed by Caltech in Pasadena, oversees GRACE-FO operations for NASA’s Earth Science Division within the Science Mission Directorate in Washington. GRACE-FO builds on its predecessor’s legacy by refining the monitoring of global water movement, sea-level rise, and other climate-related changes, offering essential insights for understanding and responding to Earth’s evolving environment.
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4 Comments
The above NASA press release does not mention uncertainties for the measurements. Fortunately, the cited article, which applies to this summary, does provide estimated uncertainties for the loss of glacial ice from Greenland and Antarctica, among other measurements. Although, the original article doesn’t explicitly define whether the margin of error is to have an associated probability of 68% (1-sigma) or 95% (2-sigma). Because this is a climatology article, I will assume that the uncertainties are for a 1-sigma probability. How a peer-reviewed article makes it through peer review without indicating the probability range of the asserted uncertainty escapes me. It does not speak well for the rigor of the research, which I frequently criticize.
The article states, “Most of the barystatic gain is attributed to ablation of polar ice sheets and glaciers. GRACE and GRACE-FO … data indicate that the Greenland and Antarctic ice sheets have contributed 261 ± 45 GT/yr and 104 ± 57 GT/yr [respectively] to BSL since 2002 (Velicogna et al. 2020).”
Because there is so much concern and press about antarctic ice losses, particularly West Antarctica, let’s take a closer look at the antarctic numbers: “104 ± 57 GT/yr.” That means that the uncertainty actually has a 95% probability (± 2-sigma) of being between ± 114 GT/yr. Another way of stating this is that annual ice loss (barystatic ocean gain) is 104 GT/yr ±110%. It should be obvious that the measurements are neither very precise or accurate when the uncertainty is greater than 100% of the nominal measurement. That may be a clue to the curious why uncertainties are so frequently left out of climatology studies, and commonly restricted to 1-sigma when provided, while physicists are comfortable reporting precision to 6-sigma and higher. I guess if one has bragging rights it is understandable that they will be used.
Wether accurate or not we are feeling the effects everyday specially in Australian farms!
Because there is a fixed amount of water on the planet, what you are observing is a change in precipitation patterns — weather. Surely, you don’t expect the same amount of rain in the same location, every year! If you get more some years, isn’t it reasonable you will get less in other years? Much of Australia is desert. Guess what defines a desert.
If you have little regard for accuracy, do you count your change when you purchase something? Do you check your monthly utility bills to be sure that you aren’t being overcharged?
A previous article came to a different conclusion:
https://scitechdaily.com/17-years-of-gravity-observations-show-how-earths-water-cycle-is-ramping-up-as-climate-warms/