2℃ of global warming would put pressure on Melbourne’s water supply



Sunburnt Victorian fields are set to become more common under climate change.
Fir0002/Flagstaffotos/Wikimedia Commons, CC BY-NC-SA

Ben Henley, University of Melbourne; Andrew King, University of Melbourne; Anna Ukkola, Australian National University; Murray Peel, University of Melbourne, and Rory Nathan, University of Melbourne

Melbourne’s existing water supplies may face pressure if global warming hits the 2℃ level, according to our new research published today in Environmental Research Letters.

The effects of drying and warming in southern Australia are expected to reduce natural water supplies. If we overshoot 2℃ of warming, even the desalination plant might not provide enough drinking water to a growing population.

However, keeping warming to 1.5℃ would help avoid many of these negative consequences. This brings home the local benefits of acting swiftly to limit global warming. Luckily, there are options available to secure our water supply.

Warming and drying effects

The Earth has warmed by about 1.1℃ since pre-industrial times, causing ongoing global changes to our atmospheric composition. The Paris Agreement commits the world to holding the increase to “well below” 2℃, and “pursuing efforts” to limit the increase to 1.5℃.

While we’re confident there will be more hot extremes and fewer cold extremes as global temperatures rise, the consequences of further global warming for other climate extremes – such as drought – in different parts of the world are harder to pinpoint.




Read more:
Is Australia’s current drought caused by climate change? It’s complicated


Our study uses climate models to identify the possible changes in average rainfall and temperature in four different worlds:

  • the “Natural” world, where humans have had no influence on the climate,

  • the “Current” world, which approximates the impacts humans have had to date, and

  • two future worlds, which are “1.5℃” and “2.0℃” warmer than pre-industrial times.

In line with previously published results, southern Australia is projected to undergo drying and warming. But we are not alone. The Mediterranean and Southwestern North America are also predicted to dry out.

Desalination is increasingly important

Most Australians recall the severity and length of the Millennium Drought. This event severely stressed agricultural and natural systems, and led to the commissioning of desalination plants in the five largest cities in Australia, at a cost of several billion dollars.

Desalination offers an important lifeline. Although it comes with high short-term costs, it supplies vital water security over the long term. Successful efforts to improve water-use efficiency have reduced per capita demand rates, but growing populations in major centres will lead to increasing water demand.

Rainfall deficiencies over Australia for the 18 months between 1 Feb 2018 and 31 July 2019.
Bureau of Meteorology

Right now, large parts of southeastern Australia are in the grips of another drought. Although drought is a common natural feature of Australia’s climate, in recent decades we have observed long-term drying trends over much of southern Australia.

Currently, all capital city urban reservoir systems in southern Australia are below 60%, and several are nearing or below 50%. The Victorian government recently ordered 125 gigalitres of water from the desalination plant.

Urban water storage levels for Australia’s capital cities.
Bureau of Meteorology

With these challenges in mind, our paper explores the effects of future climate change on the surface water supply infrastructure for Melbourne.

Climate models and hydrological models together indicate future declines in catchment inflows as global warming increases from 1.5℃ to 2℃. The good news is when desalination is added to the mix, which it is, pressure on our water storage is dramatically reduced. However, population growth and climate change remain key challenges into the future.

The buffer is shrinking

The take-home message is, if global warming approaches 2℃ and beyond, the combined impacts of climate change and population growth will ultimately begin to outstrip the buffer desalination provides for us without ongoing investment in water security. Fortunately, desalination plants, storm water, water recycling and continuing to improve efficiency are all viable options.

To ensure our water security, and with it, the safety and prosperity of the urban centres which are the engine houses of the Australian economy, we all need to be vigilant in managing water resources.

We also all need to play an active part in the global effort to reduce the impacts of climate change. The commitments by the world’s nations for the 2020-30 period remain insufficient to achieve the temperature goals. Global emission rates continue to rise, and atmospheric greenhouse gas concentrations are steadily accelerating.

The task of turning around our emissions in time to avert many of the serious impacts of climate change is becoming ever more implausible. In the coming 10–20 years, we expect to shoot past 1.5℃.




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With so much momentum in both human and natural systems it is becoming increasingly unlikely that we will avoid warming beyond 1.5℃. However, if we can achieve it, the list of benefits includes greatly reduced stress on the water supplies we rely on for our very existence.The Conversation

Ben Henley, Research Fellow in Climate and Water Resources, University of Melbourne; Andrew King, ARC DECRA fellow, University of Melbourne; Anna Ukkola, Research Associate, Climate Change Research Centre, Australian National University; Murray Peel, Senior lecturer, University of Melbourne, and Rory Nathan, Associate Professor Hydrology and Water Resources, University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Logging must stop in Melbourne’s biggest water supply catchment


File 20181113 194488 ixuwud.png?ixlib=rb 1.1
Clearfell logging in the Thomson Catchment with the Thomson Reservoir in the background.
Chris Taylor

David Lindenmayer, Australian National University and Chris Taylor, Australian National University

Continued logging in Melbourne’s water catchments could reduce the city’s water supply by the equivalent of 600,000 people’s annual water use every year by 2050, according to our analysis.

We calculated water lost due to logging in the Thomson Catchment, which is the city’s largest and most important water supply catchment. Around 60% of Melbourne’s water is stored here.

Since the 1940s, 45% of the catchment’s ash forests (including mountain and alpine ash forest) have been logged. There are plans to log up to a further 17% of these forests under the VicForest’s existing logging plan.

Past logging in the ash forests has reduced the Thomson Catchment’s water yield, which is the amount of water that flows through the catchment, by 15,000 megalitres (a megalitre is a million litres) each year. This equates to around 9% of water yield from ash forests across the catchment.

By 2050, continued logging in these forests at the current rates could increase this loss to 35,000 megalitres each year, or 20% of water yield. This will be equal to the water use of around 600,000 people every year, based on estimated water use of 161 litres per person each day.

Thomson Catchment showing the extent of ash forest, with historic and planned logging (left) and annual rainfall distribution (right).
DELWP, 2018; Xu and Hutchinson 2018; DSE 2007.



Read more:
Ashes to ashes: logging and fires have left Victoria’s magnificent forests in tatters


Why forests are important for water supply

The city of Melbourne has some of the best quality water in the world. A key reason for this is that the city’s first water infrastructure planners closed many of the key water catchments to intensive human disturbance, such as logging.

But there also can be competition for water between different land uses in catchments that are not closed and open to logging. Indeed, it has long been known that logging can significantly reduce the amount of water produced from forests, especially those close to Melbourne.

Research on forest hydrology shows that the amount of water yielded from ash forests is related to forest age. Catchments covered with old-growth ash forests yield almost twice the amount of water each year as those covered with young forests aged 25 years. This is because evapotranspiration, the process by which trees transpire water into the atmosphere as well as evaporation from the surrounding land surface, is higher in young forests compared with older forests.

Up to 200,000 trees per hectare germinate following logging or an intense fire which burns the whole stand. Intense competition between young trees results in rapid growth rates along with increased evapotranspiration. As the forest matures, the trees thin out, and after 200 years, an ash forest can have less than 50 trees per hectare. These older ash forests release more water back into the catchment.




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With logging occurring every 60-120 years, large areas of ash forest are kept in a high evapotranspiration stage of growth, therefore releasing less water back into the catchment.

Perhaps the losses in water yield could be justified if the value of the timber and pulpwood produced from logging exceeded the value of water. However, previous research has shown that the water in these areas is 25.5 times more valuable than the timber and pulpwood from ash forests.

What can the Victorian government do?

The ash forests in the Thomson Catchment are logged primarily for paper manufacturing. Under the Forest (Wood Pulp Agreement) Act 1996, the Victorian government is bound to supply Australia’s largest pulp and paper mills at Maryvale, owned by the Nippon Paper Group, with at least 350,000 cubic metres of native forest logs each year. The Thomson Water Supply Catchment is allocated for logging under this Act.

If logging was stopped in the catchment, what is the alternative for these paper mills? The answer is to source wood from current plantations. In 2017, Victoria produced 3.9 million cubic metres of logs from plantations. This could supply the pulp and paper mills at Maryvale several times over.

A challenge facing Victoria’s forest industry is the loss of jobs. One major factor in this is out-of-state processing. Australia tends to import lower volumes
of more processed and higher value wood products, including printing and writing paper. By contrast, higher volumes of less processed and lower value wood products, such as woodchips and unprocessed logs – largely from plantations, are exported.

Redirecting plantation sourced logs and woodchips from export markets to domestic processing can address some of these problems. In fact, detailed analysis suggests doing this would have an overall positive economic impact for Victoria.

Stopping logging in the Thomson Catchment and sourcing instead from well managed plantations could both boost water supply and create more jobs. Of course, some jobs would be lost for people who log from the catchment, but this would be more than compensated for by employment in the plantation processing sector.

The first Wood Pulp Agreement Act of 1936, which legislated supply of pulplogs from Victorian state forest to earlier paper manufacturers in Maryvale, featured a clause stating logging was to cease following the designation of the Thomson Catchment in 1967. This has clearly not occurred. In fact 63% of logging in the ash forests across the catchment has occurred since 1967.

The Thomson Catchment is the only one of Melbourne’s large water supply catchments open to logging. Given the critical importance of the Thomson Catchment, our work clearly indicates the Victorian government needs to cease logging and prioritise the supply of water to the people of Melbourne.The Conversation

David Lindenmayer, Professor, The Fenner School of Environment and Society, Australian National University and Chris Taylor, Research Fellow, Fenner School of Environment and Society, Australian National University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

When climate change hits our food supply, city foodbowls could come to the rescue


Rachel Carey, Deakin University; Jennifer Sheridan, University of Melbourne, and Kirsten Larsen, University of Melbourne

Australians may need to get used to coping with more disruptions to their food supply and rising food prices in a warming climate.

But the food produced near our cities – our “city foodbowls” – could play a vital role in increasing the resilience of our food supply, as discussed in a new briefing from our Foodprint Melbourne project.

The urban fringes of Australia’s major cities are some of the most productive agricultural regions in Australia. They also have access to valuable urban waste streams to support food production, including recycled water from city water treatment plants and desalination plants.

Nonetheless, Australia’s city foodbowls are at risk of urban development, and the opportunity to develop them as climate resilient foodbowls could be lost unless their value is recognised in metropolitan planning policy.

Climate shock

The Queensland floods of 2010-11 showed how a sudden extreme weather event could disrupt a city’s food supply. Major transport routes to Brisbane and other cities were cut off and supermarkets began to run short of some food.

And the Millennium Drought demonstrated the impact that drought could have on food prices, when fruit prices in Australia increased 43% between 2005 and 2007, and vegetable prices by around 33%.

Climate change is expected to reduce the capacity for food production across southern Australia due to water scarcity, increasing temperatures and more frequent extreme weather events.

We don’t know exactly how climate change will affect food production, but it is likely that Australia’s major regional foodbowl, the Murray-Darling Basin, will see significant impacts in a severe drying scenario. Wheat and dairy production are predicted to decrease due to climate change. Crops such as fruit and vegetables are likely to be particularly affected.

As the impacts of climate change are felt in Australia’s regional foodbowls, urban and urban fringe (or “peri-urban”) areas of food production around Australian capital cities could become more important sources of fresh foods. Cities have access to resources that are in increasingly short supply, such as water, fertile land and organic waste streams that can be composted to provide fertilisers.

Australia’s city foodbowls

These urban fringes are not widely-recognised as “foodbowls”, but historically they have been an important source of food. Like many world cities, they were typically founded in fertile areas with good access to water. This fed their growing populations.

As cities sprawl, market gardens have been pushed further out and city foodbowls have shrunk, but many are still highly productive. Sydney’s foodbowl produces at least 20% of New South Wales’ total vegetable production, for instance, including the majority of the state’s total production of cabbage, spring onions, shallots and mushrooms.

Melbourne’s foodbowl produces a wide variety of foods, including fresh vegetables, fruit, eggs and meat. It currently has the capacity to meet up to 41% of the food needs of city’s population.

Crops such as lettuce are commonly grown on the urban fringes of cities thanks to close access to markets and labour
Rachel Carey

Some areas of Melbourne’s foodbowl have access to recycled water, such as Werribee to the city’s west and the proposed Bunyip Food Belt to the south-east. The Werribee Irrigation District, next to Melbourne’s Western Treatment Plant, grows around 10% of the vegetables produced in Victoria, including the majority of the state’s broccoli and cauliflower.

Towards the end of the Millennium Drought, vegetable production in this region became dependent on recycled water from the water treatment plant as river levels fell.

But areas such as Werribee are under threat from urban development.

Resilient food supply

The importance of city foodbowls for resilient and sustainable food systems has been recognised internationally.

Cities such as Melbourne and Sydney are fed from a variety of sources – regional, national and global – as well as local. All are important, but urban and urban fringe food production has the potential to increase the resilience of a city’s food supply in a number of ways. These include reducing the dependence of city populations on distant sources of food, and maximising the use of limited natural resources.

If Australia’s capital cities are able to accommodate growing populations in a way that contains urban sprawl and retains their capacity for food production, city foodbowls could contribute to a food supply more resilient from climate change.

For this to happen, city planning strategies need to recognise the significance of city foodbowls for sustainable and resilient city food systems.

The Conversation

Rachel Carey, Research Fellow, Deakin University; Jennifer Sheridan, Researcher in sustainable food systems, University of Melbourne, and Kirsten Larsen, Manager, Food Systems Research and Partnerships, University of Melbourne

This article was originally published on The Conversation. Read the original article.

Article: Climate Change Impact on South Africa


The following article reports on the threat to South Africa’s water supply by climate change.

http://www.livescience.com/20413-warmer-climate-deprive-south-africa-water.html