Arresting the water flow for good

Behind the worsening fire danger we face each season is the change in the way water is being distributed across our country. It’s still the same volume of water but it’s no longer being held and managed in our traditional water supplies – and that’s the problem

Sit back – make a cup of tea or pour a long drink as you need to read how the water you depend on is being diverted away from its traditional path.

The report you are about to digest is thorough, compelling and painstakingly researched.

Scientists believe we are already experiencing megafires and that they will continue to increase in the future. They are characterised as very large, fast-moving, and exceptionally intense fires that are capable of burning vast swaths of land – consuming hundreds of thousands of hectares and thousands of homes – and the likelihood of large, fast-moving, and dangerous wildfires will continue to increase in the coming decades

Water, a seemingly free elixir that life itself depends upon is no longer running the same course – and may never do so again.

A global study has found a gaping wound: our water supplies are shrinking at the same time as weather patterns are 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 is conclusive – the most exhaustive global analysis of rainfall and rivers – and is highly credible as it was carried out by a team at the University of New South Wales (UNSW).

Led by Prof Ashish Sharma the study relied on actual data from 43,000 rainfall stations and 5,300 river monitoring sites in 160 countries.

This process was conducted in real-time, and not based on model simulations of a future climate, which can be uncertain and at times questionable.

Large rivers drying out

For anyone with their eyes open and a skerrick of attachment to their surroundings, it is clear that streams and rivers have been drying up for many years and continue to do so.

“This is something that has been missed,” said 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.

“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.

Water management has perhaps rarely been in our control – but unless that changes and we take a more proactive approach to storing and managing its flow we will find ourselves sitting on a dune hill in a desert surrounded by flood water that is worse than useless

Blue water’ vs ‘green’

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 soaked up by the landscape and the ecosystem.

How the flow has changed
The way we have been capturing water reserves simply doesn’t work anymore. This chart is based on the most recent monitoring and shows how the flow pattern has changed. We need to change our habits with it

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.”

‘Call to action’

Prof Mark Hoffman, UNSW’s Dean of Engineering, welcomed Sharma’s research and called for a national 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.”

In a paper published in the American Geophysical Union’s Water Resources Research, Sharma and colleagues write that despite widespread global evidence of rising precipitation extremes, evidence is pointing more towards decreased flood peaks for the moderate flood events that form the key refill  in water supply reservoirs.

“While extreme floods may increase due to the larger storms that are occurring, these floods are often too large to be stored for water supply.

It is the less extreme floods our reservoirs depend on,” Sharma said.


Large declines in soil moisture

The study suggests that large declines in the amount of moisture in the soil, coupled with the contraction in the geographical spread of each storm event, are the immediate reasons why increases in extreme rainfall are not resulting in corresponding increases in flooding.

They point to previous U.S. research that shows that, in extreme rainfall events, if surrounding soils are wet before a storm, 62% of the rain leads to flooding that can be captured by catchments.

But when soils are dry, only 13% of the rain results in flooding.

“This is kind of contradicting the increasing flood argument in past IPCC reports, but pointing to possibly a far worse scenario,” said Sharma.

“Small floods are very important for water supply, because they refill dams and form the basis of our water supply,” said Sharma.

“But they’re happening less often, because the soils are sucking up the extra rain. Even when a major storm dumps a lot of rain, the soils are so dry they absorb more water than before, and less reaches the rivers and reservoirs.”

Reduced flows into reservoirs

Past research has so far missed this. “Everybody has been obsessed by the flood side of the equation but have ignored the more critical component, which is the embattled water supply that comes from reduced flows into our reservoirs,” he added.

And the possible solution. “One option is to wait for international agreements to take effect, so greenhouse gas concentrations can be reined in – but this will take a long time.

The other option is to be proactive, and re-engineer our water systems so we can better adapt and cope.”

To adapt to this reality, new policies and infrastructure is needed. In areas where water supply is shrinking, water-intensive farming will need to be moved elsewhere, while reservoir storage capacities will need to be expanded.

In urban areas, where flooding is becoming more common, we need to store flood water.

Re-engineering on a massive scale

“We need to adapt to this emerging reality,” said Sharma.

“We’re going to need re-engineering on a massive scale in some places if we are to continue living in them.

And 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 liveable.

“Or take the Snowy Mountain Scheme: it’s not just about hydroelectricity, it’s also a complex water supply scheme with 225km of tunnels, pipelines and aqueducts.”

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 far worse.”

Intense flooding in urban areas

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 IPCC 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 flood water and releases it later. You never see floods there now.”

Climate will continue along its own way and beat us badly if we try to fight it. Instead of ignoring these obvious changes we simply have to adapt and work with, what is, a new set of natures’ rules.