The Human Fingerprint on Earth’s Water Cycle - NASA Earth Observatory

Image of the Day for October 20, 2026

Human activities have become intertwined with how water is distributed across the continents. A new study brings their effects into sharper focus.

Measurements from NASA’s GRACE (Gravity Recovery and Climate Experiment) and GRACE-FO (GRACE Follow-On) missions reveal trends in terrestrial water storage from April 2002 to November 2025. Areas outlined in black indicate where trends showed strong associations with human activities. Trends are depicted in terms of average annual change in equivalent water depth.

NASA Earth Observatory/Michala Garrison, based on data from O’Neill, M.M., et al.

Humans are exerting increasing influence over how water moves through lakes, rivers, soil, and the subsurface, and a new NASA study shows where those effects are greatest. Using more than two decades of satellite measurements of subtle changes in Earth’s gravity, the researchers sharpened the picture of how—and why—terrestrial water storage has changed.

This map encapsulates their findings, depicting changes in terrestrial water storage from April 2002 to November 2025. Beyond the influence of climate variability, the scientists identified 40 regions where the changes also aligned with human activities such as irrigation, reservoir impoundment, and land-use change. These activities were significantly related to terrestrial water storage trends on every nonpolar continent except Australia.

In some areas, the effects of human activities were especially strong. “In four continental regions, an anthropogenic variable showed a stronger relationship with the storage trends than any climate variable did,” said Mary Michael O’Neill, a hydrologist at NASA’s Goddard Space Flight Center and lead author of the study.

They include well-known spots such as California’s Central Valley and northern India, where farmers’ heavy reliance on groundwater has drawn down storage—in India’s case, faster than earlier estimates suggested. Elsewhere, some types of farming and water management appear to have done the opposite.

Gravity as a Water Gauge

The data behind the map come from the GRACE (Gravity Recovery and Climate Experiment) and GRACE-FO (GRACE Follow-On) missions, each of which consists of two satellites that fly in tandem. As the lead satellite passes over an area with greater mass, the slight change in gravity tugs at it, and instruments aboard the satellites measure the change in distance between them. Since water and ice are heavy and shift around regularly, scientists can use GRACE data to infer gains and losses.

The satellites’ data are typically processed into monthly maps that show broad patterns of water storage. But over more than 20 years, the satellites have passed over most of the planet many times. By combining all of those passes, the researchers could map long-term water trends with five to 10 times more spatial detail than previous analyses. The tradeoff was a loss of temporal detail. They then applied statistical techniques to weigh the importance of various anthropogenic and climatic factors in the storage trends and to pinpoint where human activities may have contributed.

The improved spatial resolution uncovered some human impacts that had not been previously detected, said Matthew Rodell, deputy director of Earth Sciences for Hydrosphere, Biosphere, and Geophysics at Goddard and one of the study’s authors. The analysis also showed that some known trends were stronger than previously realized.

Where the Water Went

Across several continents, groundwater-irrigated farmland was strongly associated with declines in terrestrial water storage. In North America, these declines appeared in California’s Central Valley, the southern High Plains of the U.S., and Chihuahua, Mexico, where long-term droughts have increased farmers’ reliance on groundwater. Groundwater pumping also drove declines in northern India, where the refined analysis showed a steeper downward trend than previously realized. Consistent with previous findings, retreating Himalayan glaciers accounted for only 15 percent of the decline there.

Other types of agriculture had a different relationship with water storage trends. In parts of sub-Saharan Africa, for example, some increases occurred where rainfed cropland has expanded. There, swaths of native savanna were replaced by millet cultivation throughout the study period, and water tables rose despite below-average precipitation. A similar pattern emerged in northern Brazil’s Maranhão state, where soybean fields have replaced forests and shrublands. The resulting water storage trend might be explained in part by the efficient water use of cereal and legume plants and by Indigenous practices that help direct water into shallow aquifers, the researchers said.

Water storage and diversion projects also came into focus on the new map. Hundreds of large reservoirs were filled during the study period, the authors note, but the coarse spatial resolution of gravity measurements previously made them difficult to track. In the new analysis, the Boguchany Reservoir on Russia’s Angara River, the second-largest reservoir filled in the 21st century, produced the strongest water storage trend in nonpolar northern Asia.

A segment of the Karakum Canal, which diverts river water to irrigate cropland in the desert, is visible as a linear, vegetated feature in this photo, taken by an astronaut aboard the International Space Station on June 13, 2021.

The map also resolves smaller reservoirs and other hydrologic engineering projects. The Karakum Desert in Turkmenistan registered water storage gains stemming from the long, largely unlined Karakum Canal running through it. The canal diverts river water to support desert agriculture, but enough seeps into the ground during its journey to alter the water picture in the desert. The map’s finer resolution allows for better monitoring of such hydrologic changes in remote areas where other measurement options may be limited.

Moving forward, O’Neill wants to capture how dams, diversions, irrigation, and other controls on Earth’s water affect storage downstream, and to disentangle the influence of local and non-local activities. “I’d also like to recover more of the temporal picture,” she said. One way to do that is by combining the higher-resolution data with standard monthly products or by applying the recent technique over shorter timeframes. “This could help track how localized trends evolve in response to specific events like droughts or policy changes.” 

Source: The Human Fingerprint on Earth’s Water Cycle - NASA Science

How a Rare Fibronectin Mutation May Protect High-Risk APOE4 Carriers From Alzheimer’s

APOE ε4 is the strongest common genetic risk factor for Alzheimer’s disease, and roughly one in five people carries at least one copy. Carrying it raises the likelihood of developing the disease, but it does not guarantee it. Some carriers remain mentally sharp well into their 80s, and scientists have long wondered what protects them.

A team at Columbia University now reports a biological mechanism that may help explain that resilience. The study, published in Nature Aging on September 11, 2026, centers on a protein called fibronectin and on the blood-brain barrier, the protective lining of the brain’s blood vessels.

The genetic clue

The new work builds on a study the same group published two years ago. It found that some people who carry APOE ε4 also carry a rare protective mutation in the fibronectin gene, FN1. Fibronectin helps support tissue structure, but in people with APOE ε4, excess amounts can build up around blood vessels in the brain and may compromise the blood-brain barrier. The rare FN1 mutation appears to limit that buildup and the damage linked to it.

That raised a question the new study sets out to answer: why is excess fibronectin harmful in the first place? In the words of corresponding author Caghan Kizil, the study moves “from a genetic clue to a disease mechanism.”

Why the blood-brain barrier matters

The blood-brain barrier is made of tightly connected cells around the brain’s blood vessels. It regulates which substances can pass from the bloodstream into brain tissue and helps maintain the conditions needed to clear waste. When it becomes damaged or too permeable, substances that are normally kept out can get in more easily, which may contribute to inflammation and other processes involved in neurological disease.

What the researchers did and found

The team combined many approaches: human brain tissue and cerebrospinal fluid analyzed with genetic and epigenetic methods, single-cell sequencing, spatial imaging, human stem-cell models, three-dimensional blood vessel cultures, and experiments in zebrafish and mice. Across these methods the findings pointed the same way.

·         APOE ε4 drives fibronectin buildup. Mice engineered to carry human APOE ε4 had nearly twice as much fibronectin in the brain as mice carrying APOE ε3, another common version of the gene, along with signs of a leaky blood-brain barrier.

·         Fibronectin does more than accompany the damage. Raising fibronectin specifically in astrocytes, the support cells that help maintain the barrier, was enough to make it more permeable. Lowering fibronectin improved barrier function.

·         A signaling pathway is disrupted. Excess fibronectin activates abnormal signals through integrins, proteins that help cells sense their surroundings, and an enzyme called focal adhesion kinase. These signals disturb a network of growth factors (VEGF, HBEGF and IGF1) that astrocytes and blood vessel cells use to coordinate and keep the barrier intact.

·         Human samples show a similar pattern. In brain tissue and cerebrospinal fluid, higher fibronectin was associated with inflammation in astrocytes, and genetic analyses linked FN1 to blood vessel disease and to VEGFA, a growth factor important for healthy brain vessels.

Possible routes to treatment

The mechanism suggests three possible strategies: preventing harmful amounts of fibronectin from accumulating around brain blood vessels, blocking the abnormal signals that excess fibronectin triggers, or restoring the growth factor signaling that keeps the barrier healthy. The researchers are investigating these in laboratory experiments.

Turning this into a therapy will not be simple. Fibronectin has essential roles throughout the body, including supporting tissue structure and helping damaged tissue heal, so any treatment would need to target its harmful accumulation or effects without disrupting those functions. The team also suggests the work could help identify the best time to intervene and provide ways to measure whether a treatment is protecting the brain.

How to read these results

The strongest causal evidence, that raising fibronectin opens the barrier and lowering it helps, comes from cell and animal experiments. The human data show associations consistent with the same process, which strengthens the case but does not prove that the mechanism operates identically in people. No therapy based on this work has been tested in humans, and the researchers describe the potential treatments as still under laboratory investigation. For now this is a well-supported mechanism and a promising target, not a treatment or a way to prevent Alzheimer’s.

One more piece of context: according to the press release, Kizil and two co-authors, Richard Mayeux and Badri Vardarajan, are founders and shareholders of KVM Therapeutics and are inventors on patent applications related to FN1-targeted therapeutic approaches. That does not invalidate the findings, but it is relevant when weighing optimism about future drugs.

This post is a summary based on the Columbia University Irving Medical Center press release. For full methods, statistics and limitations, see the original paper.

Sources

·         Press release: The Brain’s Blood Vessels May Hold a Key to Alzheimer’s – and Protection From It (Columbia University Irving Medical Center, September 11, 2026)

·         Original paper: Bhattarai P, Yilmaz E, et al. Fibronectin mediates APOE4-driven blood-brain barrier dysfunction in Alzheimer’s disease. Nature Aging 2026; 6(9): 1901. DOI: 10.1038/s43587-026-01204-0

Source: How a Rare Fibronectin Mutation May Protect High-Risk APOE4 Carriers From Alzheimer’s