December 17, 2018

The Long Dry: Why the world's water supplies are shrinking (?)

Uni NSW has now released a slightly more scholarly version -- in part below -- of their implausible  claim that the world is drying out.  But it still makes no sense.  They now admit that it sounds crazy to say a warmer world would be dryer amid increased rainfall but still say it will be.

Their basic datum is reduced flows in many rivers and they say that is because the soils are sucking up more of the rain than they used to.  That's still pretty crazy.  They are saying that soils will be dryer in a rainier world.  There's a bridge in Brooklyn they might like to buy.

There's a blindingly obvious explanation for reduced river flows: Diversion of water for human and animal use, particularly irrigation. Farmers worldwide are always putting in dams and diversions. Prof. Sharma sounds Indian so let me tell him how it's done in Australia.

When rains are good and river flows are up, farmers lucky enough to have a river nearby dig a big hole in their land and cut a channel from the river to that hole.  The hole fills up, the channel is blocked and that hole becomes a dam which can supply water next year when the rains fail.  There are dams like that all along Australia's inland rivers.  See Cubbie station for a large scale example.

And every one of those dams will reduce river flow.  They really will!  Need I go on?


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 Prof Ashish Sharma at the 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.

Large rivers drying out

“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.

'Blue water' vs 'green water'

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.”

Media release: CONTACT Prof Ashish Sharma  +61 425 332 304 | a.sharma@unsw.edu.au





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