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Study Reveals Dramatic Decline in Global Freshwater Resources
A collaborative effort by an international team of scientists, utilizing data from NASA and German satellites, has uncovered a significant drop in the planet’s total freshwater supply that began suddenly in May 2014, a trend that has persisted since then. Their findings, published in Surveys in Geophysics, indicate that Earth’s continents may have transitioned into a long-term drier period.
Between 2015 and 2023, satellite data revealed that the average quantity of freshwater stored on land—comprising surface water found in lakes and rivers, as well as underground aquifers—was approximately 290 cubic miles (1,200 cubic kilometers) lower than the levels recorded from 2002 to 2014. Matthew Rodell, a hydrologist at NASA’s Goddard Space Flight Center and co-author of the study, emphasized the magnitude of this loss, equating it to a volume two and a half times that of Lake Erie.
The dependency on groundwater has escalated during droughts, especially with the significant expansion of irrigated agricultural practices. This reliance can create a downward spiral: as surface freshwater supplies dwindle and precipitation fails to replenish groundwater, increased pumping depletes these underground reserves further. A recent United Nations report highlighted the risks associated with such water scarcity, noting potential consequences like famine, conflict, poverty, and heightened disease risks due to reliance on contaminated water sources.
The abrupt global reduction in freshwater was identified through observations from the Gravity Recovery and Climate Experiment (GRACE) satellites, a collaborative project involving the German Aerospace Center, the German Research Centre for Geosciences, and NASA. These satellites track shifts in Earth’s gravitational field over time, providing insights into variations in water mass above and below the surface. The original GRACE satellites operated from March 2002 until October 2017, and were succeeded by the GRACE-Follow On (GRACE-FO) satellites, launched in May 2018.
The onset of this freshwater decline was linked to a severe drought in northern and central Brazil, followed by significant drought conditions across Australasia, North America, Europe, and Africa. Warmer ocean temperatures in the tropical Pacific during late 2014 through 2016 contributed to one of the most intense El Niño events since 1950, resulting in altered atmospheric patterns and subsequent changes to global weather and rainfall distribution. Despite the subsiding of El Niño, freshwater stocks have not rebounded; in fact, the study indicates that 13 of the globe’s 30 most severe droughts tracked by GRACE occurred post-January 2015. Researchers suspect that ongoing global warming may play a role in this persistent depletion of freshwater resources.
According to NASA Goddard meteorologist Michael Bosilovich, global warming causes the atmosphere to retain increased amounts of water vapor, which can lead to more extreme weather events like intense precipitation. While annual totals of rain and snow might not vary drastically, extended dry spells between significant rainfall events lead to soil desiccation and compaction, which hinders its ability to absorb future rain. “When extreme precipitation occurs, much of it runs off rather than soaking in, which means it doesn’t replenish groundwater levels,” Bosilovich explained.
Although there are strong indicators that the freshwater decline is largely influenced by climate change, establishing a direct causative link remains challenging. Susanna Werth, a hydrologist and remote sensing scientist at Virginia Tech, pointed out potential obstacles: “There are uncertainties in climate predictions. Measurements and models always come with errors.”
The future trajectory of global freshwater reserves remains uncertain. Whether levels will rebound to what was observed prior to 2015, stabilize, or continue their decline is unclear. With the nine hottest years on record aligning with the notable drop in freshwater, Rodell cautions that this pattern is likely not merely coincidental, suggesting it could signal ongoing challenges ahead.
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