Freshwater change
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The alteration of the freshwater dynamics that regulate the climate, maintain ecosystems, and support the fundamental conditions required for people and societies to thrive.
Human actions change how freshwater flows and stocks are distributed on land and in the atmosphere. Specifically greenhouse gas emissions, irrigation and other water uses, water infrastructures, and the expansion of agricultural land have changed the global water cycle.
This has pervasive impacts on freshwater resources; the occurrence of droughts and storms has increased, while groundwater stocks are under depletion and river flows to the ocean are widely disrupted. The Planetary Boundary for freshwater change measures how far streamflow and soil moisture conditions have deviated from a quasi-stable state that is largely unaffected by human actions.
Anomalously dry or wet streamflow and soil moisture conditions now occur on approximately double as large land areas than under pre-industrial-like conditions, due to extensive human impacts on the freshwater cycle. This surpasses the safe limit for human modification of the water cycle and places the Freshwater Change boundary in the increasing risk zone. Increasing freshwater anomalies undermine terrestrial and aquatic ecosystem integrity and modify land carbon balance. They also critically change water availability for human uses.
Control Variables
The Planetary Boundary for Freshwater Change looks at two main parts of the global water cycle: blue water and green water. Blue water is the water we can see and use — in rivers, lakes, and underground aquifers. Green water is the moisture stored in the soil that plants rely on to grow and that helps drive rainfall through evaporation.
Both types of water are now under serious pressure. Rivers are drying up or flooding at the wrong times, Climate Change and deforestation are changing rainfall patterns, and soils are drying out and losing their ability to hold water. These disruptions make it harder for people and nature to access the water they need, and increase the risk of droughts, floods, and widespread ecosystem damage.
Impacts
Water is essential for life, linking the atmosphere, land, and biosphere through a delicate global cycle. When this balance is disrupted — by overuse, shifting rainfall patterns, or the loss of forests and vegetation that help regulate water flow — the consequences ripple through the Earth system. Conditions that are too dry or too wet threaten biodiversity, alter local and regional climates, and jeopardize food and water security for millions of people.
Current state
The boundary has been crossed for both control variables.
The nine planetary boundaries
This text is a summary of the latest Planetary Health Check.
More info about this boundary, its key drivers and details of how the control variables are measured can be found on www.planetaryhealthcheck.org
The latest peer-reviewed update to all planetary boundaries was published in in Science Advances in 2023.
In 2024, researchers could show that the planetary boundary on freshwater has been crossed since the mid-twentieth century.
