Is Perth really running out of water? Well, yes and no


File 20180213 44642 1985p1v.jpg?ixlib=rb 1.1
The future of Perth’s urban wetlands is in doubt.
Orderinchaos/Wikimedia Commons, CC BY-SA

Don McFarlane, University of Western Australia

As Cape Town counts down to “day zero” and the prospect of its taps being turned off, there have inevitably been questions about whether the same fate might befall a major Australian city. The most striking parallels have been drawn with Perth – unsurprisingly, given its drying climate, rising evaporation rates (which increase consumption and reduce water yields) and growing population.

So is Perth really running out of water? The answer depends on what type of water is being considered, and what constitutes “running out”.




Read more:
Cape Town is almost out of water. Could Australian cities suffer the same fate?


When faced with this question most people think of drinking water, which is of course essential for household use.

It often ignores non-potable groundwater that is heavily relied upon in Perth to irrigate gardens, lawns, ovals, golf courses and market gardens. This water is also used by light and heavy industry, as well as being crucial to the health of wetlands and vegetation across the coastal plain.

Lake Jualbup in Perth’s western suburbs showing periods of low and high water level. Photos by Geoffrey Dean.
saveourjewel.org, Author provided

Perth’s drinking water supplies are largely safe, thanks to early investment in the use of groundwater and in technologies such as desalination. But somewhat ironically, as this recent book chapter explains, the future supply of lower-quality water for irrigation and to support ecosystems looks far less assured.

A drying climate

Perth’s annual rainfall has been declining by about 3mm per year on average, while the number of months receiving at least 200mm of rain has halved. Meanwhile, the annual mean temperature anomaly has increased by 1℃ in southwest Western Australia in the past 40 years and possibly by more in Perth, given the urban heat island effect.

Perth’s rainfall trend, as measured at Perth Airport’s rain gauge.
Bureau of Meteorology

The overall effect is that soils and vegetation are often dry, meaning that rainfall will be lost to evapotranspiration rather than running off into rivers and dams, or recharging underground aquifers.

At the same time, Perth has made major changes to its drinking water supply. The city now relies chiefly on groundwater and desalination rather than dams. For a variety of reasons, drinking water use per person has declined, most notably since the early 2000s when sprinkler restrictions were introduced. Some have switched to self-supply sources such as backyard bores, so for them total water use may even have increased.

Perth’s trends in runoff, population, and water supply.
Water Corporation

The reduction in per capita use of drinking water is just as well, because inflows into Perth dams have fallen from 300 billion litres a year to less than 50 billion. This disproportionate drop in stream flows, even against the backdrop of declining rainfall, means that evaporation from reservoirs can exceed inflows in very dry years.

Since the late 1970s, Perth has increasingly used groundwater rather than dam water. Seawater desalination has also grown to almost half of total supply. Even more recently Perth began trialling a groundwater replenishment scheme to recharge aquifers with treated wastewater.

With the declines in rainfall and streamflow predicted to continue, water security will continue to be an important policy issue over the next few decades. Although both are much more expensive than dam water, desalination and groundwater replenishment look set to secure Perth’s drinking supply, because seawater is virtually unlimited, and wastewater availability increases in line with the city’s growth.




Read more:
This is what Australia’s growing cities need to do to avoid running dry


Why are non-drinking water supplies less secure?

Boosting drinking water supplies with desalination or groundwater replenishment is unlikely to resolve the pressures on non-potable supplies. To understand why, it is necessary to understand Perth’s unusual hydrology.

Most of Perth is built on permeable sand dunes, which can soak up even the heaviest rainfall. This allows runoff from roofs and roads to be directed into nearby soak wells and absorption basins.

As well as cheap disposal of stormwater, the sands provide Perth with a place to store excess water from winter rains, which is then relied upon for summer irrigation. As a result, local governments have been able to provide many irrigated parks and sports ovals, and more than a quarter of Perth households use a private bore to water their gardens.

This arrangement isn’t as sustainable as it once was. Groundwater levels are falling under many parts of Perth, forcing the state government to reduce allocations and to introduce a range of water-saving measures such as winter sprinkler bans.

Unlike dam inflows, we don’t yet know the full scale of the reduction in natural groundwater recharge rates. But the question still remains: what can we do to halt the decline of this important water store, particularly as Perth’s population is expected to grow to 3.5 million by 2050?

About 70% of local road runoff and half of roof runoff already recharges the shallow unconfined aquifer, because it is the cheapest way to dispose of excess water in areas with sandy soils. As well as reducing discharge costs, this practice helps to ensure that bores do not run dry in summer.

Perth also has large main drains that are designed to lower groundwater levels in swampy areas and prevent inundation. Some of these waters could be redirected into the aquifer where there is a suitable site.

Don’t waste wastewater

About 140 billion litres of treated wastewater are discharged into the ocean every year in the Perth-Peel region. A further 7 billion litres are infiltrated into the sands as a means of disposal where there isn’t an option for ocean outfall. Recent investigations of these land disposal sites have shown them to be effective in protecting wetlands from drying and providing water for public and private irrigation.

Investigations have also shown that the quality of treated wastewater can be greatly improved when infiltrated through the yellow sands into the limestone aquifer in the western part of Perth. It is suitable for irrigation after a few weeks’ residence within the aquifer.




Read more:
‘Drought-proofing’ Perth: the long view of Western Australian water


Without these kinds of measures, local governments will struggle to water parks and sports ovals, to protect Perth’s remaining wetlands, and to safeguard the trees that help keep us cool.

The ConversationSo while drinking water supplies for an affluent city like Perth are reasonably secure, our vital non-drinking water supplies need to be augmented using some of the water we currently discharge into the ocean. As Perth gets even hotter and drier, and green spaces and wetlands are needed to provide much-needed cooling, we can no longer afford to let any water go to waste.

Don McFarlane, Adjunct professor, University of Western Australia

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

Squandering riches: can Perth realise the value of its biodiversity?


Julian Bolleter, University of Western Australia

Perth is not known as a model for suburbia and its suburban condition is similar to that of developed cities the world over. However, it does stand out in one respect: it sits in an exceptionally biodiverse natural setting. A strong, informed vision for this setting’s relationship with the city could help Perth become an exemplar for similarly positioned metropolises everywhere.

The greater Perth region has been designated the Southwest Australia Ecoregion (SWAE). This is one of only 35 “biodiversity hotspots” in the world.

Reconciling future growth with biodiversity is a key issue for urban design and planning this century. Indeed, if current trends continue, global urban land cover will increase by 1.2 million square kilometres (equivalent to half the area of Western Australia) by 2030. Much of this will happen in biodiversity hotspots.

This is important because it is estimated we will lose nearly half of all terrestrial species if we fail to protect the hotspots. We will also lose the ecosystem services upon which human populations ultimately depend.

If we fail to protect the world’s 35 biodiversity hotspots we risk losing nearly half of all terrestrial species.
Conservation International, Author provided

“Ecosystem services” may sound like abstract jargon, but it’s actually a term used to describe the services nature provides – such as clean air, water and food, and heatwave and flood mitigation. Without these, human life would be extremely unpleasant, if not unviable.

Perth has a reputedly strong planning system and is comparatively wealthy. If it can’t control its city form to protect biodiversity – compact cities generally being recognised as the best model for protecting land for conservation – then city administrators elsewhere, particularly in the developing world, are likely to struggle.

Misreading the land

The current treatment of the Australian environment has its roots in the European annexation of Australia, which has been characterised by catastrophic misreadings of the land. Governor James Stirling, who was singularly responsible for the European annexation of Perth, was the kind of man who saw what he wanted to see rather than what was there. In The Origins of Australia’s Capital Cities, Geoffrey Bolton writes:

…arriving at the end of … an uncommonly cool, moist summer, [Stirling was] misled by the tallness of the northern jarrah forest and the quality of the alluvial soils close to the river into believing that the coastal plain would offer fertile farming and grazing. It was, Stirling wrote, equal to the plains of Lombardy; and he persuaded himself that the cool easterly land breeze of these early autumn nights must originate from a range of snowy mountains.

Vegetation of Southwest Australia Ecoregion near current-day Perth at the time of European settlement. Based on statewide mapping by John Beard between 1964 and 1981.
DPAW
Remnant vegetation of SWAE near Perth in 2015.
DPAW/WALGA, courtesy of AUDRC, Author provided

The results of such misinterpretations of the land were generally less poetic. Stirling sited the settlement of Perth on a narrow, constrained strip of land between swamps to the north and marshy river edges to the south. These low-lying areas fuelled plagues of mosquitos and, once polluted, deadly typhoid outbreaks.

In time, due to a lingering discomfort with Perth’s “unsanitary” wetlands, more than 200,000 hectares – an area equivalent to 500 Kings Parks – were drained on the Swan Coastal Plain. These biologically productive areas directly or indirectly support most of the coastal plain’s wildlife, so the effects on biodiversity have been catastrophic.

Furthermore, a perception of the Banksia woodland and coastal heath on Perth’s fringes as unattractive and useless has seen much of it cleared for the expansion of the city. Between 2001 and 2009, suburban growth consumed an annual average of 851ha of highly biodiverse land on the urban fringe.

The lesson from this experience is that any future growth in a biodiversity hotspot, or indeed elsewhere, has to be founded on the understanding that we cannot continue to bend nature to our will. We must learn how to work with it.

Within this humbling process, we need to recognise that working with the land is not an entirely pure or noble act; rather, it is imperative for humanity’s survival. As species and ecosystems become threatened and vanish, so too do the ecosystem services that support human wellbeing.

Perth’s Green Growth Plan

The release of the state government’s long-anticipated Perth and Peel Green Growth Plan for 3.5 million may herald a shift in the relationship between the city and the biodiversity hotspot. The plan encapsulates two broad goals:

  • to protect fringe bushland, rivers, wetlands and wildlife in an impressive 170,000 hectares of new and expanded reserves on Perth’s fringe

  • to cut red tape by securing upfront Commonwealth environmental approvals for outer suburban development.

Proposed new and existing reserves – light and dark green respectively – on Perth’s fringe (indicative only).
DOP, courtesy of AUDRDC, Author provided

While ostensibly positive achievements, a question remains as to the implications of clearing a further 45,000ha (3% of the Swan Coastal Plain) of remnant bushland which is not protected by the conservation reserves.

Furthermore, the typically disconnected conservation reserves proposed in the Green Growth Plan lack overall legibility. This stymies the public’s ability to conceptualise the city’s edge, which leads them to care about it (like London’s greenbelt, for instance).

Finally, a question remains about how a plan that places restrictions on outer suburban development will accommodate the powerful local land development industry over time. This is a concern given the frequent “urban break-outs” – where urban development occurs outside nominated growth areas – between 1970 and 2005.

In 2003, the ABC asked revered Western Australian landscape architect Marion Blackwell, “Are we at home now in the land we live in?” She replied, “No, we’re not. We don’t know enough about it, and not enough people know anything about it.”

We still have work to do on our engagement with biodiversity in Western Australia, and Perth specifically, before we can become a model for future cities.


The Conversation is co-publishing articles with Future West (Australian Urbanism), produced by the University of Western Australia’s Faculty of Architecture, Landscape and Visual Arts. These articles look towards the future of urbanism, taking Perth and Western Australia as its reference point. You can read other articles here.

The Conversation

Julian Bolleter, Research Fellow, Australian Urban Design Research Centre, University of Western Australia

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

Cocky count: how Perth’s ‘green’ growth plan could wipe out WA’s best-loved bird


Robert Davis, Edith Cowan University and Martine Maron, The University of Queensland

Carnaby’s black cockatoo lives only in southwestern Australia. Although a much-loved cultural icon, it is now facing a major threat to its persistence: urban growth. Will Western Australia’s favourite bird survive Perth’s expansion?

It is already listed as endangered under state and federal legislation. Historical land clearing has decimated Carnaby’s numbers, felling their breeding grounds and reducing their range. Today, the birds are thought to be using all of their remaining habitat, which is barely enough to sustain the population.

Current distribution range of Carnaby’s black cockatoos.
Joseph Forshaw/Wikimedia Commons, CC BY-SA

But there is a major new threat to this charismatic cockatoo. The new “Green Growth Plan” for Perth and the nearby Peel region could pave the way for the clearing of tens of thousands of hectares of important feeding and roosting habitat, in the name of urban development.

A rocky road ahead

State environment minister Albert Jacob has claimed that the Green Growth Plan is “the absolute best opportunity” for the cockatoo population’s long-term survival.

But under the current draft plan, which is open for public consultation until May 13, Carnaby’s will lose more than 50% of their remaining feeding habitat in the Perth-Peel region, with a proportionate decline possible if key food resources are lost.

Perth’s unique Banskia woodlands are the critical native feeding habitat for Carnaby’s Black-Cockatoo.
Robert Davis, Author provided

The Carnaby’s is already declining at an alarming rate, according to BirdLife Australia’s Great Cocky Count – one of the largest citizen science surveys of its kind in Australia.

The past six years of Great Cocky Counts suggest that the population has dropped by 15% each year. Without drastic action, the window of opportunity to save this population is rapidly closing.

Yet instead of addressing this decline, the Green Growth Plan is poised to lock in destruction of more than 30,000 hectares of Carnaby’s habitat, because the conservation measures it proposes are more than cancelled out by the loss of habitat in areas of prime habitat that are zoned for urban development.

New foods

In response to dwindling natural food sources, the adaptable Carnaby’s black cockatoos have been feeding on non-native pine plantations since the 1940s. These plantations have become even more important to the species as remaining native habitat continues to be cleared.

At their peak, Perth’s Gnangara pine plantation provided 23,000 ha of prime feeding and roosting habitat. One study found that the plantations support several thousand Carnaby’s black cockatoos from January to June each year, and more than half (59%) of the birds counted in the Perth region in 2014 were associated with Gnangara.

However, since 2004 these pines have been harvested without replacement. The plantations stand over an underground aquifer called the Gnangara Mound, one of Perth’s most important water resources. With Perth’s rainfall continuing to decline while the city’s water needs grow, the pines are no longer seen as a responsible use of water.

As removing the pines will increase recharge of the aquifer, the WA government has decided that the pines will have to go.

Even though the pines are not native, their loss will have a major impact on a species already imperilled by habitat loss. Many birds are likely to starve when the food source on which they have come to rely is taken away.

Why the Green Growth Plan doesn’t stack up

So what does the Green Growth Plan offer to protect the cockatoos in the face of the planned habitat loss? Unfortunately, not a lot.

In exchange for the loss of more than 14,000 ha of native habitat and 24,000 ha of pine forest in the Perth-Peel region, the plan proposes that 5,000 ha of pines should be replanted. But young pines take many years to produce the same amount of food as established trees, so there will be a time lag before the food source is even partly replaced.

The plan also proposes to increase the level of protection of more than 100,000 ha of existing feeding habitat. But of course, that habitat is already there, and is being used by the cockatoos. Most of it is also already protected to some degree, which raises questions about how much genuine benefit schemes like this really provide.

The bottom line is that less habitat cannot sustain the same number of cockatoos. They and other species that rely on Banksia woodlands of the Swan Coastal Plain have been suffering from Perth’s unchecked urbanisation for many decades.

For the Perth-Peel plan to truly be considered green, the needs of a growing city must be balanced fairly against preservation of our unique flora and fauna by prioritising habitat retention and looking to alternatives to the ongoing loss of critical habitat.

This article was co-authored by Tegan Douglas and Sam Vine of Birdlife Australia.

The Conversation

Robert Davis, Senior Lecturer in Vertebrate Biology, Edith Cowan University and Martine Maron, ARC Future Fellow and Associate Professor of Environmental Management, The University of Queensland

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