Climate change is producing more rain, but the world’s water supply is shrinking – and now scientists know why.
Scientists have warned that global warming is drying out the planet’s soil, which could create a world where “drought-like conditions become the new normal.”
A largest-ever study of global rainfall and rivers has revealed exactly why Earth’s water supplies are struggling. Their findings were published in Water Resources Research.
Rather than relying on simulations, scientists at the University of New South Wales in Australia collected data from 43,000 rainfall stations and 53,000 river-monitoring sites – across 160 countries globally.
Researchers hoped to solve a climate mystery: Rainfall is increasing, so why are water supplies shrinking?
A recent estimate from the United Nations suggested that nearly half of the world’s population would live in areas of “high water stress” by 2030.
“This is something that has been missed,” said study author professor Ashish Sharma.
“We expected rainfall to increase since warmer air stores more moisture – and that is what climate models predicted too.
“What we did not expect is that, despite all the extra rain everywhere in the world, is that the large rivers are drying out.”
Scientists have blamed the “drying of soils” for the reduction in water supplies.
Areas with significant rainfall are generally deemed better for farming.
Typically this heavy rainfall will soak the ground and then excess water will run off into rivers.
These rivers are perfect for agriculture – allowing farmers to grow healthy, well-watered crops.
But if the soil is too dry, this runoff never happens.
“Where once these were moist before a storm event – allowing excess rainfall to run off into rivers – they are now drier and soak up more of the rain, so less water makes it as flow,” Sharma explained.
“Less water into our rivers means less water for cities and farms. And drier soils means farmers need more water to grow the same crops.
“Worse, this pattern is repeated all over the world, assuming serious proportions in places that were already dry.”
Sharma called it “extremely concerning.”
For every 100 raindrops that fall on land, just 36 are “blue water.”
This is the rainfall that enters lakes, rivers and aquifers – the water extracted for human needs.
The rest of the rainfall is retained as soil moisture, also known as “green water.”
Warming temperatures are causing more water to evaporate from soils.
These soils then absorb more rainfall when it does occur, leaving less “blue water” for humans to use.
“It’s a double whammy,” Sharma warned.
“Less water is ending up where we can store it for later use.
“At the same time, more rain is overwhelming drainage infrastructure in towns and cities, leading to more urban flooding.”
According to the professor, governments will need to “adapt to this emerging reality.”
“We’re going to need re-engineering on a massive scale in some places if we are to continue living in them.
“But it’s possible: places like Arizona and California receive barely 400mm of rain each year, but have engineered their water supply systems to make previously uninhabitable places livable.”