Australia is facing more severe floods and droughts as rainfall patterns diminish over the past three decades, a new report has warned.

Co-author Professor Will Steffen from the Climate Council said the report shows an intensification of drought and floods.

“Climate change is shifting our rainfall patterns and increasing the severity of droughts and floods. We’ve always been a sunburnt country, but things are getting worse,” he said.

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The Murray-Darling Basin alone, which produces a third of the country’s food supply, has experienced a 41 per cent decline in flow by over the last 20 years, according to the report.

Co-author Lesley Hughes said that is going to have significant impact on drought-affected farmers and agricultural production and exports.

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"Australia’s water cycle is like it is on steroids due to climate change," she said.

She said the sharp decline in rainfall has exacerbated the impacts of droughts and floods.

“During droughts as water dries up in streams, rivers and dams. We get increasing concentrations of salt, of nutrients and sediments – and that all affects our water supply,” Professor Hughes said.

Bureau of Meteorology/Climate Council

“At the other end of the spectrum, we see severe impacts on health. Because we get flooding of sewage treatment plants and we have seen increases in the past in Australia, increases in outbreaks like Giardia and Cryptosporidium which mean we have to boil water.”

Seven climate change experts have authored the report, which collates the scientific peer-reviewed literature from the last few decades to give an overall picture of rainfall decline, drought exacerbation and flooding intensity.

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Sydney, Melbourne to among hardest areas hit

The report states Australia’s most populated cities will be among the areas hardest hit in coming decades, with the declining rainfall resulting in a reduced water supply.

“Basically the desalination plants that we put in place - about six of them at the cost 10 billion - they will help us for the next 10-15 years,” said report co-author, Professor Rob Vertessy.

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“But after that population growth will mean that we will have to consider new augmentations in many of our big capital cities.”

The former head of the Bureau of Meteorology said the projected population growth of an extra 3 million people in both Sydney and Melbourne by mid-century is a concern.

‘Climate refugees affect regional security’

Professor Vertessy said mass migration of climate refugees would impact on regional security.

“I think the whole world has to face up the problem of the mass migration of climate refugees,” he said.

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“There are some serious hotspots at the moment for water security, particularly for the Middle East and the North Africa region. And some of the countries in South Asia that are below the Himalayas that depend on glacial melt water.

“If you look out far enough, it seems very clear to me and people who are watching this, that there will be large parts of the world that won't be able to support the populations that they currently support.”

Government urged to act

Professor Hughes said there is an urgent need for a stronger federal government climate policy, saying that phasing out coal would be the best long-term solution.

“As we're all aware Australia has no federal climate policy. Australian emissions have been rising every quarter since March 2015. Australia is lagging beind the rest of the world when we should be leading on climate change action.

“So it is extremely important, if we are able to stablilise the climate by the second half of this century that we have rapid and deep emission cuts. We need federal leadership on this.”

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Government defends 'strong' climate policy

Finance Minister Mathias Cormann has insisted the federal government's climate change policy is "strong" and "effective".

WA Liberal senator Dean Smith has challenged the government to strengthen its policy to appeal to the youth vote based a Newspoll analysis.

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The poll results showed 27 per cent of 18 to 34-year-olds would allocate their primary vote to the coalition, compared with 46 per cent who would support Labor.

Senator Cormann told the ABC he believes the federal government's policy doesn't need changing.

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"We are dealing with climate change," he told the ABC.

"But in a way that doesn't undermine the opportunity for young people in particular to get a job, to build a career in Australia into the future.

"My view and our view is that we have to continue to take strong and effective action in relation to climate change but in a way that is economically responsible."