A recently published paper by NASA scientists has found unprecedented changes in the global water cycle due to human intervention. These shifts range from declining groundwater levels to extreme events like increased frequency of “100-year floods.”
Many of these changes are driven by human activities like agriculture and could affect ecosystems and water management, particularly in certain regions.
“We established with data assimilation that human intervention in 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 study, which was published in the Proceedings of the National Academy of Sciences.
These shifts have global implications. Water management strategies — such as flood infrastructure design and drought indicators for early warning systems — are often based on the assumption that the water cycle fluctuates within a predictable range, according to Wanshu Nie, a research scientist at NASA Goddard and the study’s lead author.
“This may no longer hold true for some regions,” Nie said. “We hope this research will guide improvements in how we assess water resource variability and plan for sustainable management, particularly in areas where these changes are most pronounced.”
One example of human impact on the water cycle can be seen in North China, where an ongoing drought persists. Despite this, vegetation continues to flourish in many areas, partly because farmers are pumping additional water from groundwater reserves to irrigate their land, Kumar explained. Such interconnected human interventions often lead to complex changes in other water cycle components, like evapotranspiration and runoff.
Nie and her team focused on three types of shifts in the water cycle: first, a trend, such as the declining water levels in a groundwater reservoir; second, a shift in seasonality, like an earlier growing season or earlier snowmelt; and third, a change in extreme events, like the increased frequency of “100-year floods.”
The researchers used remote sensing data from 2003 to 2020, sourced from multiple NASA satellites, including 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 the Moderate Resolution Imaging Spectroradiometer satellite instrument to monitor vegetation health.
“This paper combines several years of our team’s efforts in developing satellite data analysis capabilities, enabling us to accurately simulate continental water fluxes and storage across the globe,” said Augusto Getirana, a research scientist at NASA Goddard and co-author of the study.
The findings suggest that Earth system models used to predict future global water cycles should evolve to account for the ongoing effects of human activities. With more data and improved models, water resource managers and producers could better understand and plan for the "new normal" of their local water situations, Nie concluded.