In a recently published paper, NASA scientists use nearly 20 years of observations to show that the global water cycle is changing in unprecedented ways. Most of these changes are caused by activities such as agriculture, and may have impacts on ecosystems and water management, especially in certain regions.
“Through data assimilation, we found that human interference with the global water cycle is more significant than we thought,” said Sujay Kumar, a research scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and co-author of the paper published in Proceedings of the National Academy of Sciences. National Academy of Sciences.
These changes have implications for people around the world. Water management practices, such as designing infrastructure for floods or developing drought indicators for early warning systems, are often based on assumptions that the water cycle fluctuates only within a certain range, said Wanshu Ni, a NASA Goddard scientist and lead author of the paper.
“This may be unfair to some regions,” said Ni. “We hope this study will serve as a guide to improve how we assess water resource variability and plan for sustainable resource management, especially in areas where these changes are most significant.”
One example of human influence on the water cycle is northern China, which is experiencing a persistent drought. But vegetation in many areas continues to thrive, in part because farmers continue to irrigate their land, drawing more water from groundwater storage, Kumar said. Such interconnected human interventions often lead to complex impacts on other water cycle variables, such as evapotranspiration and runoff.
Ni and her colleagues focused on three different types of shifts or changes in the cycle: first, a trend, such as a decrease in water in a groundwater reservoir; second, a change in seasonality, such as the typical growing season starting earlier in the year or early snowmelt; and third, a change in extreme events, such as “100-year floods,” occurring more frequently.

The scientists collected remote sensing data from 2003 to 2020 from several different NASA satellite sources: the Global Precipitation Measurement mission satellite for precipitation data, a soil moisture dataset from the European Space Agency's Climate Change Initiative, and the Gravity Recovery and Climate Experiment satellites for terrestrial water storage data. They also used products from the satellite's Medium Resolution Spectroradiometer instrument to provide information on vegetation status.
"This paper brings together several years of effort from our team to develop satellite data analysis capabilities that allow us to accurately simulate continental water flows and water supplies across the planet," said Augusto Getirana, a NASA Goddard scientist and co-author of the paper.
The study's findings suggest that Earth system models used to model the future of the global water cycle need to evolve to integrate the current impacts of human activities. With more data and improved models, producers and water resource managers could understand and effectively plan for what the "new normal" local water situation looks like, Ni said.