The study's findings indicate that the planetary boundary for freshwater change, a threshold delineating the safe operating space for humanity, was breached as early as the mid-twentieth century. This breach underscores a century-long trend of human-induced stress on the Earth's freshwater systems, which has pushed them beyond the stable conditions that supported ecological and climatic processes for millennia.
Led by an international team of researchers, including Vili Virkki of Aalto University, the study employed hydrological models to calculate monthly streamflow and soil moisture across the globe with a spatial resolution of approximately 50x50 kilometers. These models integrated all major human impacts on the freshwater cycle, from dam construction and large-scale irrigation to the effects of global warming. By comparing the industrial period (1861-2005) against a pre-industrial baseline (1661-1860), the researchers could quantify the deviations in dry and wet conditions across the global land area.
Their analysis revealed a near doubling in the global land area experiencing significant deviations from pre-industrial conditions, with a marked increase in the frequency of exceptionally dry or wet conditions. These deviations have become more frequent and widespread, particularly since the early 20th century, highlighting the altered state of the global freshwater cycle due to human activity.
The research also uncovered geographical variations in these deviations. Many tropical and subtropical regions are experiencing more frequent exceptionally dry conditions, while boreal and temperate regions are seeing an uptick in exceptionally wet conditions, particularly in soil moisture. These patterns are consistent with the changes in water availability attributed to climate change. However, regions with a long history of human land use and agriculture, such as the Nile, Indus, and Mississippi river basins, exhibit more complex patterns of change, driven by factors like irrigation.
The study's co-lead, Miina Porkka, emphasized the importance of using consistent and comparable methods across hydrological variables and geographical scales to understand the biophysical processes and human actions driving these changes. This comprehensive view allows researchers to better investigate the causes and consequences of alterations in the freshwater cycle.
Matti Kummu, Associate Professor at Aalto University and the senior author of the study, stressed the urgency of reducing human-driven pressures on freshwater systems. He highlighted the importance of understanding these dynamics in detail to guide policies aimed at mitigating harm and preserving the vital role of freshwater systems in supporting life on Earth.
This research underscores the critical need for immediate action to alleviate the human impact on the planet's freshwater resources, ensuring their capacity to regulate vital ecological and climatic processes remains intact.
Research Report:Notable shifts beyond pre-industrial streamflow and soil moisture conditions transgress the planetary boundary for freshwater change
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