The amount of freshwater on Earth has seen a significant decrease since May 2014, and this reduced level has persisted. This change might suggest that the continents are facing a long-term drier period.
An international group of scientists, utilizing data from NASA-German satellites, discovered that the Earth’s freshwater supply saw a sharp decline beginning in May 2014, with low levels continuing to this day. In a report published in Surveys in Geophysics, the researchers proposed that this change could signal a prolonged dry phase for the Earth’s continents.
Between 2015 and 2023, satellite data indicated that the average freshwater available on land, which encompasses surface water such as lakes and rivers as well as groundwater, was 290 cubic miles (1,200 cubic km) less than the average from 2002 to 2014. Matthew Rodell, a hydrologist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and one of the study’s authors, commented, “That’s two and a half times more water lost than the volume of Lake Erie.”
During droughts and with the expansion of irrigated farming, reliance on groundwater increases for both agriculture and urban areas. This reliance can create a cycle that reduces underground water resources: as freshwater supplies dwindle and rainfall doesn’t replenish them, more groundwater is extracted. The drop in accessible water impacts farmers and communities, which can escalate into issues like famine, conflict, poverty, and higher disease risks as people may resort to using contaminated water, according to a 2024 UN report on water stress.
The research team detected this sudden global drop in freshwater through data from the Gravity Recovery and Climate Experiment (GRACE) satellites, managed by the German Aerospace Center, German Research Centre for Geosciences, and NASA. The GRACE satellites track monthly changes in Earth’s gravity that indicate variations in water mass above and below the surface. The original GRACE satellites operated from March 2002 until October 2017, while the newer GRACE-Follow On (GRACE-FO) satellites were launched in May 2018.
The study noted that the global decrease in freshwater began with significant drought conditions in northern and central Brazil, quickly followed by major droughts in regions such as Australasia, South America, North America, Europe, and Africa. The rise in ocean temperatures in the tropical Pacific, leading to significant weather shifts, along with one of the most notable El Niño events since 1950, altered global weather and rainfall patterns starting in late 2014 and continuing into 2016. However, after the El Niño event ended, global freshwater levels did not recover. In fact, Rodell and his team found that since January 2015, 13 of the 30 most severe droughts recorded by GRACE occurred. They suspect that global warming may be influencing the ongoing reduction in freshwater supply.
According to NASA Goddard meteorologist Michael Bosilovich, global warming causes the atmosphere to retain more water vapor, leading to more severe precipitation events. Although the total annual precipitation may not significantly decrease, extended intervals between heavy rainfall can lead to soil drying and compaction. This compaction diminishes the ground’s ability to absorb water during rainfall.
“When extreme precipitation occurs,” Bosilovich explained, “it often runs off rather than soaking in, which means groundwater is not getting replenished.” Since the El Niño event from 2014-2016, freshwater levels globally have remained consistently low, while additional water has become trapped in the atmosphere as vapor. “Rising temperatures increase the evaporation of water and the atmosphere’s ability to hold water, which raises the frequency and intensity of drought,” he added.
While it seems that global warming is a primary factor in the sudden drop of freshwater, linking the two factors definitively poses challenges. Susanna Werth, a hydrologist and remote sensing expert at Virginia Tech who did not participate in the study, noted, “There are uncertainties in climate predictions. Measurements and models have inherent errors.”
It remains uncertain whether global freshwater levels will rise back to pre-2015 proportions, stabilize, or continue to decline. Since the nine hottest years on record align with the significant drop in freshwater, Rodell stated, “We don’t see this as a coincidence, and it could be a warning of future trends.”
