NASA Satellites Reveal Abrupt Drop in Global Freshwater Levels - EARTH

GRACE satellites measure gravity as they orbit the planet to reveal shifting levels of water on the Earth (artist's concept).

NASA/JPL-Caltech

An international team of scientists using observations from NASA-German satellites found evidence that Earth’s total amount of freshwater dropped abruptly starting in May 2014 and has remained low ever since. Reporting in Surveys in Geophysics, the researchers suggested the shift could indicate Earth's continents have entered a persistently drier phase.

From 2015 through 2023, satellite measurements showed that the average amount of freshwater stored on land — that includes liquid surface water like lakes and rivers, plus water in aquifers underground — was 290 cubic miles (1,200 cubic km) lower than the average levels from 2002 through 2014, said Matthew Rodell, one of the study authors and a hydrologist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “That’s two and a half times the volume of Lake Erie lost.”

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. 

This map shows the years that terrestrial water storage hit a 22-year minimum (i.e., the land was driest) at each location, based on data from the GRACE and GRACE/FO satellites. A significantly large portion of the global land surface reached this minimum in the nine years since 2015, which happen to be the nine warmest years in the modern temperature record.

Image by NASA Earth Observatory/Wanmei Liang with data courtesy of Mary Michael O’Neill

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. 

“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.”

By James R. Riordon
NASA’s Earth Science News Team  

Source: NASA Satellites Reveal Abrupt Drop in Global Freshwater Levels - NASA Science  

NASA’s Curiosity Mars Rover Takes a Last Look at Mysterious Sulfur - UNIVERSE

 

Use your mouse to explore this 360-degree view of Gediz Vallis channel, a region of Mars that NASA’s Curiosity rover surveyed before heading west to new adventures. NASA/JPL-Caltech/MSSS

The rover captured a 360-degree panorama before leaving Gediz Vallis channel, a feature it’s been exploring for the past year.

NASA’s Curiosity rover is preparing for the next leg of its journey, a monthslong trek to a formation called the boxwork, a set of weblike patterns on Mars’ surface that stretches for miles. It will soon leave behind Gediz Vallis channel, an area wrapped in mystery. How the channel formed so late during a transition to a drier climate is one big question for the science team. Another mystery is the field of white sulfur stones the rover discovered over the summer.

Curiosity imaged the stones, along with features from inside the channel, in a 360-degree panorama before driving up to the western edge of the channel at the end of September.

The rover is searching for evidence that ancient Mars had the right ingredients to support microbial life, if any formed billions of years ago, when the Red Planet held lakes and rivers. Located in the foothills of Mount Sharp, a 3-mile-tall (5-kilometer-tall) mountain, Gediz Vallis channel may help tell a related story: what the area was like as water was disappearing on Mars. Although older layers on the mountain had already formed in a dry climate, the channel suggests that water occasionally coursed through the area as the climate was changing.

Scientists are still piecing together the processes that formed various features within the channel, including the debris mound nicknamed “Pinnacle Ridge,” visible in the new 360-degree panorama. It appears that rivers, wet debris flows, and dry avalanches all left their mark. The science team is now constructing a timeline of events from Curiosity’s observations.

NASA’s Curiosity captured this panorama using its Mastcam while heading west away from Gediz Vallis channel on Nov. 2, 2024, the 4,352nd Martian day, or sol, of the mission. The Mars rover’s tracks across the rocky terrain are visible at right.

NASA/JPL-Caltech/MSSS

The science team is also trying to answer some big questions about the sprawling field of sulfur stones. Images of the area from NASA’s Mars Reconnaissance Orbiter (MRO) showed what looked like an unremarkable patch of light-colored terrain. It turns out that the sulfur stones were too small for MRO’s High-Resolution Imaging Science Experiment (HiRISE) to see, and Curiosity’s team was intrigued to find them when the rover reached the patch. They were even more surprised after Curiosity rolled over one of the stones, crushing it to reveal yellow crystals inside.

Science instruments on the rover confirmed the stone was pure sulfur — something no mission has seen before on Mars. The team doesn’t have a ready explanation for why the sulfur formed there; on Earth, it’s associated with volcanoes and hot springs, and no evidence exists on Mount Sharp pointing to either of those causes.

“We looked at the sulfur field from every angle — from the top and the side — and looked for anything mixed with the sulfur that might give us clues as to how it formed. We’ve gathered a ton of data, and now we have a fun puzzle to solve,” said Curiosity’s project scientist Ashwin Vasavada at NASA’s Jet Propulsion Laboratory in Southern California.

NASA’s Curiosity Mars rover captured this last look at a field of bright white sulfur stones on Oct. 11, before leaving Gediz Vallis channel. The field was where the rover made the first discovery of pure sulfur on Mars. Scientists are still unsure exactly why theses rocks formed here.

Spiderwebs on Mars

Curiosity, which has traveled about 20 miles (33 kilometers) since landing in 2012, is now driving along the western edge of Gediz Vallis channel, gathering a few more panoramas to document the region before making tracks to the boxwork.

Viewed by MRO, the boxwork looks like spiderwebs stretching across the surface. It’s believed to have formed when minerals carried by Mount Sharp’s last pulses of water settled into fractures in surface rock and then hardened. As portions of the rock eroded away, what remained were the minerals that had cemented themselves in the fractures, leaving the weblike boxwork.

On Earth, boxwork formations have been seen on cliffsides and in caves. But Mount Sharp’s boxwork structures stand apart from those both because they formed as water was disappearing from Mars and because they’re so extensive, spanning an area of 6 to 12 miles (10 to 20 kilometers).  

“These ridges will include minerals that crystallized underground, where it would have been warmer, with salty liquid water flowing through,” said Kirsten Siebach of Rice University in Houston, a Curiosity scientist studying the region. “Early Earth microbes could have survived in a similar environment. That makes this an exciting place to explore.” 

By: Jet Propulsion Laboratory 

Source: NASA’s Curiosity Mars Rover Takes a Last Look at Mysterious Sulfur - NASA