Why the Earth's water cycle is under threat

For the first time in recorded history the system that moves water around the planet is off balance, according to a landmark new report.

Water moves around the world in "atmospheric rivers" as part of the global water cycle , explained the report from the Global Commission on the Economics of Water. Water evaporates from ground level and rises into the atmosphere, spreading across the world as vapour before cooling, condensing and returning to the Earth as rain or snow.

However, decades of destructive land use and water mismanagement have combined with climate change to put "unprecedented stress" on this process, the commission said.

As this "rapidly accelerating water crisis grips the planet", more than half the world's food production will be "at risk of failure" within the next 25 years, said The Guardian .

Vicious cycle

The study differentiated between "blue water", found in rivers and lakes, and "green water", which is contained in soils and plant life and released into the atmosphere via transpiration. Crucially, green water has been overlooked, said the authors, noting that it accounts for around half of global rainfall.

A vicious cycle is at play: a steady supply of green water is essential for supporting vegetation that can store planet-heating carbon, but humanity's destructive path, including the destruction of wetlands and forests, is "depleting these carbon sinks" and "accelerating global warming", said CNN . The "climate-changed fuelled heat" is then "drying out landscapes, reducing moisture and increasing fire risk".

Disruptions to the water cycle are "already causing suffering", said the broadcaster , with nearly three billion people facing water scarcity around the world. Global water scarcity threatens more than 50% of global food production and risks shaving off up to 15% of countries’ GDPs by 2050. The report says people need a minimum of about 4,000 litres of water a day to lead a "dignified life", but this is more than most regions will be able to provide from local sources.

Several cities are also sinking because of the loss of below-ground water ; densely populated areas such as northwest India, northeast China, and southern and eastern Europe are expected to bear the brunt of the problem, noted NBC News .

A common good

The report makes several recommendations, including shifting from animal-based diets to transform how water is used in farming, improving efficiency, restoring natural habitats and treating and renewing more wastewater.

Richard Allan, a climate science professor at Reading University, who wasn't involved in the report, told CNN the "grim" problems it highlights can only be tackled through better management of natural resources, and huge cuts in planet-heating pollution.

Speaking to NBC News, Mariana Mazzucato, a professor and founding director of the University College London Institute for Innovation and Public Purpose, blamed a lack of collective will among governments, and market forces.

"We can do it", she said, "we've just chosen not to because we have inertia" and "because we have profits being made from not dealing with the crisis".

The huge distances that water in the atmosphere can travel means decisions made in one country can disrupt rainfall in another, so the report's authors have also called for collective effort, saying that world governments must recognise the water cycle as a "common good" and address it together.