Human activity in the past century has dramatically altered freshwater flows, jeopardising their capacity to regulate vital ecological and climatic processes, a study has found.
The paper, published in Nature Water by researchers at Finland-based Aalto University, revealed that the extent of land affected by deviations – due to global warming or the construction of dams and irrigation systems – almost doubled compared to pre-industrial conditions.
“Dry and wet deviations have consistently occurred over substantially larger areas since the early 20th century than during the pre-industrial period,” the researchers said, calling for urgent actions to reduce human disturbance of the freshwater cycle.
The report analysed shifts in streamflow and soil moisture between 1861 and 2005 compared to pre-industrial conditions, revealing a “substantial” change.
“By the end of our study period, areas with local streamflow deviations covered 18.2% – equivalent to about 24 million sq. km – of global ice-free land area.”
This corresponds to a 94% increase from the pre-industrial period, the study said.
Land use, dam construction, water extraction, and large-scale irrigation were among the drivers that extensively altered the quantity and timing of atmospheric and terrestrial freshwater flows, with “crucial” implications for Earth’s climate and ecosystems.
“Exceptional conditions are now much more frequent and widespread than before, clearly demonstrating how human actions have changed the state of the global freshwater cycle,” said Vili Virkki, a researcher at Aalto University and one of the paper’s authors.
“Comparing the two periods, we find an increased frequency of local deviations on around 45% of land area, mainly in regions under heavy direct or indirect human pressures,” the study found.
GEOGRAPHICAL DIFFERENCES
Several tropical and sub-tropical regions experienced more frequent dry streamflow and soil moisture conditions, while boreal and temperate areas faced an increase in exceptionally wet conditions.
“Using a method that’s consistent and comparable across hydrological variables and geographical scales is crucial for understanding the biophysical processes and human actions that drive the changes we’re seeing in freshwater,” Miina Porkka, who led researchers of the study, explained.
The analysis highlighted geographical differences, showing distinct patterns based on changes in water availability and the history of human land use and agriculture.
For example, the Mississippi, Indus, and Nile basins experienced alterations before 1940, while other areas, such as Siberia, South and Southeast Asia, and the Congo Basin, have only recently faced such changes – or have not faced them yet.
“By inspecting local deviation frequency on areas equipped for irrigation, we found that irrigation intensity is associated with increasing dry streamflow and wet soil moisture deviation frequency,” the researchers said.
“These cases are observed in many heavily irrigated regions, such as South Asia, Eastern China, Western US, and the Nile Delta.”
“Understanding these dynamics in greater detail could help guide policies to mitigate the resulting harm – but our immediate priority should be to decrease human-driven pressures on freshwater systems, which are vital to life on Earth,” concluded Matti Kummu, senior author of the study.
By Sergio Colombo – sergio@carbon-pulse.com
*** Click here to sign up to our twice-weekly biodiversity newsletter ***
