Freshwater Change
Boundary Breached
The alteration of freshwater cycles, including rivers and soil moisture, impacts natural functions such as carbon sequestration and biodiversity, and can lead to shifts in precipitation levels. Human-induced disturbances of both blue water (e.g. rivers and lakes) and green water (i.e. soil moisture) have exceeded the safe level.
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Importance
Our food systems, and the biodiversity of our planet, rely on healthy freshwater ecosystems. Excessive use of freshwater for agriculture, land use changes such as deforestation, and shifting weather patterns caused by climate change, are threatening supplies of freshwater.
Impacts
Transgressing the Freshwater Change boundary has significant impacts on the functioning of the Earth system, as well as on human societies.
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Disrupting the water cycle threatens the viability of entire ecosystems such as the Amazon, degrading Biosphere Integrity and ecosystem services. Human food and fodder production is especially threatened by reduced freshwater availability.
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Since human water demand peaks during droughts, water deficits resulting from withdrawals and meteorological conditions often compound, further exacerbating the impacts on ecosystems and human societies.
Control Variables
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Blue Water
Human-induced disturbance of blue water (referring to water in lakes, rivers, and reservoirs) is approximated by the annual global area with significant deviations in streamflow from pre-industrial variability. This reflects changes in surface and groundwater availability, which are crucial for the health of associated ecosystems. Local stream flow deviations have almost doubled since the late 19th century, already surpassing the Planetary Boundary at the beginning of the 20th century and continuing to rise since then.
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Green Water
Human-induced disturbance of green water (referring to the stock of soil moisture which is the water available to plants, which turns into green water flow, namely evaporation and transpiration, or vapor flows). The boundary reflects changes in soil moisture in the root zone,, impacting terrestrial ecosystems, climate regulation, and biogeochemical processes. Local soil moisture deviations have significantly increased since the late 19th century, surpassing the Planetary Boundary around 1930 and continuing to rise since then.
Global Map of Increases in Dry and Wet Episodes for Blue Water
The increase in both wet and dry extremes in streamflow deviations across large parts of the world suggests increasing variability and instability in global freshwater systems.
Global Map of Increases in Dry and Wet Episodes for Green Water
The increase in both wet and dry extremes in soil moisture deviations indicates growing variability and instability within global green water systems (water stored in soils and available for use by plants).
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Key Drivers
Human activities have extensive impacts on the global water cycle, primarily through freshwater withdrawals from rivers, reservoirs, and groundwater, which significantly affect water levels and aquatic and surrounding ecosystems. The main driver of these withdrawals is irrigation, which accounts for approximately 70% of freshwater withdrawals and 90% of consumptive water use (water not returned to the source). Major irrigation hotspots include the Indo-Gangetic Basin, northern China, the U.S. High Plains, the Central Valley of California, Egypt, and several European countries. Industry follows with 20% of freshwater withdrawals, while households account for 12%.
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Over the past century, these withdrawals, along with river diversions and dam constructions, have contributed to exceeding the blue water boundary. Additionally, land-use change and climate impacts have exacerbated transgressions of both the blue and green water boundaries.
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Freshwater Change is closely linked to with activities impacting other Planetary Boundaries. For instance, Climate Change influences droughts and floods by altering atmospheric water-holding capacity, cloud formation, and circulation patterns. Moreover, Land System Change related to deforestation, agriculture, and urbanization affects soil water-holding capacity, streamflow, and evaporation rates. This can intensify droughts and alter large-scale precipitation patterns like monsoons, creating feedback loops that further impact Climate Change.
Connected Tipping Points
If the status of this Planetary Boundary continues to deteriorate, it will push many tipping elements toward tipping, including:
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Collapse of the North Atlantic Subpolar Gyre (SPG)
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Dieback Amazon and Congo rainforest
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Collapse of the Atlantic Meridional Overturning Circulation
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Dieback of boreal forests
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Degradation of savannas and grasslands
Read more about other Boundaries
Planetary Boundary process inside Earth's safe operating space
Planetary Boundary process outside Earth's safe operating space
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