The significant decrease in freshwater resources on land and underground in the last decade has increased concerns that the Earth’s continents have entered a permanent drought phase. Scientists have found that Earth’s freshwater supply has been shrinking since 2014 due to factors such as severe droughts, increased agricultural demand and climate events such as El Niño. These observations, compiled using satellite data from NASA and Germany, point to a potentially prolonged drought phase for the planet, raising concerns about the impact of global warming on natural water resources and the suitability of this water for human and agricultural use.

Sudden changes in global freshwater

Using data from NASA and German satellites, an international group of scientists found evidence of a significant and drastic decrease in freshwater reserves on Earth since May 2014. The continuation of this decrease indicates that the planet’s continents may have entered a long-term drought phase. According to published results Geophysical Research .

Between 2015 and 2023, satellite observations showed that the average amount of freshwater stored on land, including surface water in lakes and rivers and groundwater in aquifers, was 1,200 cubic kilometers (290 cubic miles) below average levels recorded since 2002. Matthew Rodell, a hydrologist at NASA Goddard Space Flight Center and one of the study’s authors, explained the significance: “This is equivalent to losing two and a half times the volume of Lake Erie.”

During droughts, with the modern expansion of irrigated agriculture, farms and cities are forced to rely more on groundwater; This can lead to a decrease in groundwater resources: freshwater resources are depleted, rain and snow cannot replenish them, and more groundwater is pumped. According to the UN’s 2024 Water Scarcity Report, decreasing available water puts pressure on farmers and communities; When people turn to contaminated water sources, it potentially leads to hunger, conflict, poverty and increased risk of disease.

Satellite survey of global water changes

A team of researchers discovered this drastic global reduction in freshwater using observations from the GRACE (Gravity Recovery and Climate Experiment) satellites operated by the German Aerospace Center, the German Geoscience Research Center, and NASA. GRACE satellites measure fluctuations in Earth’s gravity on a lunar scale, detecting changes in the mass of water above and below the ground, also known as terrestrial water resources. The original GRACE satellites flew from March 2002 to October 2017, followed by the GRACE–FO (GRACE–Follow On) satellites, which launched in May 2018 and are shown in the artist’s image below.

The map at the top of this page shows the years when satellite data showed groundwater resources in each region reached their lowest level in 22 years. The decline in global freshwater supply began with a large-scale drought in northern and central Brazil, and was soon followed by a series of major droughts in Australia, South America, North America, Europe and Africa.

Climatic effects and permanent drought

Rising ocean temperatures in the tropical Pacific from late 2014 to 2016 culminated in one of the most significant El Niño events since 1950, leading to changes in atmospheric jet streams that altered weather and precipitation patterns worldwide. But even after El Niño subsided, global freshwater did not recover. In fact, Rodell and his team report that 13 of the world’s 30 most severe droughts observed by GRACE have occurred since January 2015. They suspect that global warming may contribute to the long-term depletion of freshwater.

NASA Goddard meteorologist Michael Bosilovich said global warming causes the atmosphere to hold more water vapor, which leads to more extreme precipitation. Although the total annual amount of rain and snowfall does not vary much, long periods between heavy rainfalls cause the soil to dry out and become more compact. This reduces the amount of water the soil can absorb when it rains.

“When there is heavy rainfall, the problem is that water flows away instead of absorbing and replenishing groundwater resources,” Bosylovic said. Globally, freshwater levels remain persistently low following the 2014-2016 El Niño, while more water remains in the atmosphere as water vapor. “Warming increases the frequency and severity of drought conditions by increasing both the evaporation of water from the surface to the atmosphere and the water retention capacity of the atmosphere,” he said.

Problems predicting water trends

While there are reasons to suspect that the sharp decline in freshwater is largely due to global warming, it can be difficult to conclusively link the two facts, said Susanna Werth, a hydrologist and remote sensing scientist at Virginia Tech who was not involved in the research. research. “There are uncertainties in climate predictions,” Werth said. “Measurements and models always contain errors.”

It is not yet known whether global freshwater will rise to pre-2015 levels, remain stable, or continue to decline. Given that the nine warmest years in modern temperature records coincided with a sharp decline in freshwater levels, Rodell said, “We don’t think it’s a coincidence, and we think it could be a harbinger of things to come.”