An international team of scientists, using observations from German satellites operated by NASA, has found evidence that the total amount of freshwater on Earth has sharply declined since May 2014 and has remained at low levels since. In a paper published in the journal Surveys in Geophysics, researchers suggest this shift may indicate that Earth’s continents have entered a phase of persistent drying.
According to Matthew Rodell, one of the study’s authors and a hydrologist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, satellite measurements revealed that between 2015 and 2023, the average amount of freshwater stored on land—comprising liquid surface water such as lakes and rivers, as well as water in underground aquifers—was 290 cubic miles (1,200 cubic kilometers) lower than the average levels recorded between 2002 and 2014. “This is two and a half times greater than the loss of Lake Erie.”
What Are the Risks?
During droughts, coupled with the modern expansion of irrigated agriculture, farms and cities rely more heavily on groundwater, which can lead to a cycle of groundwater depletion: freshwater reserves are drained, rainfall and snowmelt fail to replenish them, and groundwater is extracted in even greater quantities. Decreasing available water puts strain on farmers and communities, potentially leading to hunger, conflicts, poverty, and increased risk of disease when people turn to contaminated water sources, according to a 2024 UN report on water stress.
The research team detected this sharp global reduction in freshwater reserves using observations from the Gravity Recovery and Climate Experiment (GRACE) satellites, operated by the German Aerospace Center, the German Research Centre for Geosciences, and NASA. GRACE satellites measure fluctuations in Earth’s gravity on a monthly basis, revealing changes in water mass on the surface and underground. The original GRACE satellites operated from March 2002 to October 2017. The next-generation GRACE-Follow On (GRACE-FO) satellites were launched in May 2018.
The reduction in global freshwater reserves described in the study began with a massive drought in northern and central Brazil, which was soon followed by a series of major droughts in Australia, South America, North America, Europe, and Africa. Warming ocean temperatures in the tropical Pacific from late 2014 to 2016 culminated in one of the most significant El Niño events since 1950, which disrupted atmospheric jet streams and altered weather and precipitation patterns worldwide. However, even after the El Niño event subsided, global freshwater reserves failed to recover. Rodell and his team report that 13 of the 30 most intense droughts recorded by GRACE have occurred since January 2015. Rodell and his colleagues suspect that global warming may be contributing to the prolonged depletion of freshwater.
Connection to Global Warming
Global warming causes the atmosphere to hold more water vapor, leading to more extreme precipitation, says NASA Goddard meteorologist Michael Bosilovich. While the total annual rainfall and snowfall may not change significantly, prolonged dry periods between heavy rainfall allow soil to dry out and compact. This reduces the amount of water that the ground can absorb during rainfall.
“The problem with extreme precipitation,” says Bosilovich, “is that the water ultimately runs off instead of being absorbed and replenishing groundwater supplies.” Following the 2014–2016 El Niño, global freshwater levels have remained consistently low, while more water remains in the atmosphere as vapor. “Warming temperatures increase both the evaporation of water from the surface into the atmosphere and the atmosphere’s capacity to retain water, boosting the frequency and intensity of drought conditions,” he noted.
What to Expect in the Future
While there is reason to suspect that the sharp decline in freshwater reserves is largely linked to global warming, it may be challenging to definitively connect the two, said Susanna Wert, a hydrologist and remote sensing expert at Virginia Tech who was not involved in the study. “There is uncertainty in climate projections,” Wert said. “Measurements and models always have errors.”
It remains unknown whether global freshwater reserves will return to pre-2015 levels, stay at the same level, or resume their decline. Given that the nine hottest years on record coincide with the sharp decline in freshwater reserves, Rodell stated: “We don’t think this is a coincidence, and it may be a harbinger of what’s to come.”
