Human activities have significantly altered the freshwater cycle, threatening its ability to support vital climatic and ecological Earth system processes. A new study led by researchers at the University of Eastern Finland shows that the freshwater cycle has increasingly moved away from a stable state due to climate change and large-scale water and land use. The newly published study updates the status of the freshwater change planetary boundary, which is one of the core components in the annual Planetary Health Check reports.
The study, published in Nature Communications, examined changes in “blue water” (streamflow) and “green water” (soil moisture) between 1901 and 2019, and separated the relative impacts of direct human forcing and climate-related forcing on them. The study uses streamflow and soil moisture data produced by global hydrological models, based on which the researchers analysed the occurrence of anomalously dry and wet conditions relative to a baseline state that represents pre-industrial-like stable conditions.
According to the study, the occurrence of anomalously dry and wet conditions has approximately doubled relative to the baseline conditions, for both blue and green water. In many tropical and subtropical regions, increasing dryness is the dominant type of change, whereas anomalously wet conditions have become more frequent especially in the northern boreal zone. Globally, these changes – and the transgression of the freshwater change planetary boundary – have been driven most strongly by climatic factors. Nevertheless, direct human forcing, such as water and land use, has had a significant effect particularly on global increase in anomalously dry conditions.
“The rate of change in the freshwater cycle has accelerated in recent decades, and scientific assessments and projections of future climate change indicate that this rate is likely to accelerate even more,” says Postdoctoral Researcher Vili Virkki from the University of Eastern Finland, who led the study.
Substantial and meaningful regional variation
The study further examined the occurrence of anomalous conditions and their drivers regionally across approximately 1,300 hydrological catchments. The regional analysis highlighted not only the wide extent of changes, but also their varying types depending on whether the focus was on blue or green water, or on anomalously dry or wet conditions.
“The results clearly show that focusing only on blue water does not provide a sufficiently holistic picture of water cycle change and its potential impacts,” Sofie te Wierik from the Netherlands Environmental Assessment Agency says. “Changes vary substantially between regions, over time, and depending on which component of the freshwater cycle is being examined.”
When freshwater cycle changes faster than the environment can adapt to this change, the risks of adverse impacts increase. For example, in northern boreal regions, the study identified widespread increases in wet anomalies for both blue and green water, which are mainly driven by climatic factors.
“These changes are particularly relevant in high-latitude environments, where wetter conditions can affect processes such as permafrost thaw and result in increased greenhouse gas emissions to the atmosphere,” says Virkki. “Decomposing the regional drivers of the planetary boundary transgression is essential to help in understanding the related risks of this transgression.”
The drivers of water cycle change can also differ substantially from one region to another. In some regions in India and Central Asia, for instance, climatic factors may slightly increase seasonal water availability, but at the same time, water and land use outweigh this by their major impact on increasing dry conditions. The hydrological outcome thus depends on many complex processes, some of which are not strictly hydrological in nature.
“There are many densely populated regions in the world where the main problem is the availability and overuse of blue water, and climate change may worsen the situation in some of these regions even further,” Virkki notes. “At the same time, it is essential to recognise and account for changes and impacts in green water, often driven by climate change, which are crucial for ecosystems and rainfed agriculture, for instance.”
Investigating water cycle change in the Earth system
The new study presents some of the first published results from the European Research Council funded project AQUAGUARD, which is led by Associate Professor Miina Porkka at the University of Eastern Finland. The project seeks to establish more precise and reliable understanding of the impacts of water cycle change in the Earth system.
“The water cycle must be examined as a dynamic whole, where human-driven changes can have wide-ranging and partly even unexpected impacts,” says Virkki, who also works in the project. “That is why we are collecting and synthesising existing scientific knowledge into increasingly robust impact assessments, which is at the core of integrative scientific research.”
“Our study makes clear that returning to safe limits for the global freshwater cycle will depend on addressing climate change and land and water use as interconnected drivers of change. The findings also underscore the need to better understand how planetary boundaries interact – a task we intend to take forward,” concludes co-author Dieter Gerten from the Potsdam Institute for Climate Impact Research.
Article: Virkki, V., Andersen, L.S., te Wierik, S. et al. Regionally divergent drivers behind transgressions of the freshwater change planetary boundary. Nat Commun (2026). https://doi.org/10.1038/s41467-026-73051-x