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The drying of soils due to climate change is shrinking the world’s water supply

The long dry: why the world’s water supply is shrinking, EurekAlert, : 13-DEC-2018

Global water supplies are shrinking, even as rainfall is rising; the culprit? The drying of soils due to climate change

UNIVERSITY OF NEW SOUTH WALES A global study has found a paradox: our water supplies are shrinking at the same time as climate change is generating more intense rain. And the culprit is the drying of soils, say researchers, pointing to a world where drought-like conditions will become the new normal, especially in regions that are already dry.

The study – the most exhaustive global analysis of rainfall and rivers – was conducted by a team led by Professor Ashish Sharma at Australia’s University of New South Wales (UNSW) in Sydney. It relied on actual data from 43,000 rainfall stations and 5,300 river monitoring sites in 160 countries, instead of basing its findings on model simulations of a future climate, which can be uncertain and at times questionable

“This is something that has been missed,” said Sharma, an ARC Future Fellow at UNSW’s School of Civil and Environmental Engineering. “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.

“We believe the cause is the drying of soils in our catchments. 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.

“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. It is extremely concerning,” he added.

For every 100 raindrops that fall on land, only 36 drops are ‘blue water’ – the rainfall that enters lakes, rivers and aquifers – and therefore, all the water extracted for human needs. The remaining two thirds of rainfall is mostly retained as soil moisture – known as ‘green water’ – and used by the landscape and the ecosystem.

As warming temperatures cause more water to evaporate from soils, those dry soils are absorbing more of the rainfall when it does occur – leaving less ‘blue water’ for human use.

“It’s a double whammy,” said Sharma. “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.”

Professor Mark Hoffman, UNSW’s Dean of Engineering, welcomed Sharma’s research and called for a global conversation about how to deal with this unfolding scenario, especially in Australia, which is already the driest inhabited continent (apart from Antarctica).

“It’s clear there’s no simple fix, so we need to start preparing for this,” he said. “Climate change keeps delivering us unpleasant surprises. Nevertheless, as engineers, our role is to identify the problem and develop solutions. Knowing the problem is often half the battle, and this study has definitely identified some major ones.”

The findings were made over the past four years, in research that appeared in Nature GeoscienceGeophysical Research LettersScientific Reports and, most recently, in the American Geophysical Union’s Water Resources Research………..

Sharma said the answer was not just more dams. “Re-engineering solutions are not simple, they have to be analysed on a region-by-region basis, looking at the costs and the benefits, looking at the change expected into the future, while also studying past projects so mistakes are not repeated. There are no silver bullets. Any large-scale re-engineering project will require significant investment, but the cost of inaction could be monstrous.”

In urban areas, the reverse will be needed: flooding is becoming more common and more intense. Global economic losses from flooding have risen from an average of $500 million a year in the 1980s to around $20 billion annually by 2010; by 2013, this rose to more than US$50 billion. The Intergovernmental Panel on Climate Change expects this to more than double in the next 20 years as extreme storms and rainfall intensify and growing numbers of people move into urban centres.

Adapting to this is possible, but will require large-scale re-engineering of many cities, says Sharma. “Tokyo used to get clobbered by floods every year, but they built a massive underground tank beneath the city that stores the floodwater, and releases it later. You never see floods there now.” https://www.eurekalert.org/pub_releases/2018-12/uons-tld121118.php

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December 15, 2018 - Posted by | 2 WORLD, climate change, Reference

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