rss
16

Cape Town is almost out of water. Could Australian cities suffer same fate?

Print Friendly, PDF & Email

The Conversation

The world is watching the unfolding Cape Town water crisis with horror. On “Day Zero”, now predicted to be just ten weeks away, engineers will turn off the water supply.

The South African city’s four million residents will have to queue at one of 200 water collection points.

Cape Town is the first major city to face such an extreme water crisis. There are so many unanswered questions. How will the sick or elderly people cope?

How will people without a car collect their 25-litre daily ration? Pity those collecting water for a big family.

The crisis is caused by a combination of factors. First of all, Cape Town has a very dry climate with annual rainfall of 515mm. Since 2015, it has been in a drought estimated to be a one-in-300-year event.

In recent years, the city’s population has grown rapidly – by 79% since 1995. Many have questioned what Cape Town has done to expand the city’s water supply to cater for the population growth and the lower rainfall.

Could this happen in Australia?

Australia’s largest cities have often struggled with drought. Water supplies may decline further due to climate change and uncertain future rainfall. With all capital cities expecting further population growth, this could cause water supply crises.

The situation in Cape Town has strong parallels with Perth in Australia. Perth is half the size of Cape Town, with two million residents, but has endured increasing water stress for nearly 50 years. From 1911 to 1974, the annual inflow to Perth’s water reservoirs averaged 338 gigalitres (GL) a year.

Inflows have since shrunk by nearly 90% to just 42GL a year from 2010-2016.

To make matters worse, the Perth water storages also had to supply more people. Australia’s fourth-largest city had the fastest capital city population growth, 28.2%, from 2006-2016.

As a result, Perth became Australia’s first capital city unable to supply its residents from storage dams fed by rainfall and river flows. In 2015 the city faced a potentially disastrous situation. River inflows to Perth’s dams dwindled to 11.4GL for the year.

For its two million people, the inflows equated to only 15.6 litres per person per day! Yet in 2015/6 Perth residents consumed an average of nearly 350 litres each per day.

This was the highest daily water consumption for Australia’s capitals. How was this achieved?

Tapping into desalination and groundwater

Perth has progressively sourced more and more of its supply from desalination and from groundwater extraction. This has been expensive and has been the topic of much debate. Perth is the only Australian capital to rely so heavily on desalination and groundwater for its water supply.

Volumes of water sourced for urban use in Australia’s major cities

Australia’s next most water-stressed capital is Adelaide. That city is supplementing its surface water storages with desalination and groundwater, as well as water “transferred” from the Murray River.

Australia’s other capital cities on the east coast have faced their own water supply crises. Their water storages dwindled to between 20% and 35% capacity in 2007.

This triggered multiple actions to prevent a water crisis. Progressively tighter water restrictions were declared.

The major population centres (Brisbane/Gold Coast, Sydney, Melbourne and Adelaide) also built large desalination plants. The community reaction to the desalination plants was mixed.

While some welcomed these, others question their costs and environmental impacts.

The desalination plants were expensive to build, consume vast quantities of electricity and are very expensive to run. They remain costly to maintain, even if they do not supply desalinated water.

All residents pay higher water rates as a result of their existence.

Since then, rainfall in southeastern Australia has increased and water storages have refilled. The largest southeastern Australia desalination plants have been placed on “stand-by” mode. They will be switched on if and when the supply level drops.

Investing in huge storage capacity

Many Australian cities also store very large volumes of water in very large water reservoirs. This allows them to continue to supply water through future extended periods of dry weather.

Cape Town’s largest water storage, Theewaterskloof Dam, has run dry, but the city’s total capacity is small compared to the big Australian cities’ reserves

The three largest cities (Sydney, Melbourne and Brisbane) have built very large dams indeed. For example, Brisbane has 2,220,150 ML storage capacity for its 2.2 million residents.

That amounts to just over one million litres per resident when storages are full.

In comparison, Cape Town’s four million residents have a full storage capacity of 900,000 ML. That’s 225,000 litres per resident.

Cape Town is constructing a number of small desalination plants while anxiously waiting for the onset of the region’s formerly regular winter rains.

Source: The Conversation. Reproduced with permission. enior lecturer in Environmental Science, Western Sydney University  

Pocket
  • Gordon Bossley

    I wonder how many Cape Town households have a rainwater tank?

    • howardpatr

      I wonder how many can afford them?

    • Joe

      In the current drought of Cape Town rainwater tanks would not have made much of a difference. The rain just hasn’t rained. I’ve seen some of the news stories being shown on our news channels. Residents are already lining up at the ‘communal’ water stations. Seeing them on foot carry many empty bottles to fill which they have no hope of carrying back to their homes. It is desperate stuff. In one report I heard them say that trucking in water may have to be considered. Even the evacuation of Cape Town is being considered…4 million people…not sure how that works out.

      • Barri Mundee

        Drastic but an evacuation might have to happen. Early planning for that may be smart. Perhaps temporarily evacuating some of the population would enable the rest to survive until the rains arrive.

        CT planners clearly need to plan more LT and factor in the probability of more frequent times of low rainfall.

  • howardpatr

    Perth which is populated with so many who go about in a haze when it comes to anthropogenic climate change and the renewable energy future.

    All that land and hardly any solar?

    • Joe

      I am stunned by that usage figure form 2015/16 of 350 litres each per day, there must be a lot of ‘wastage’ in that. I wonder what the most recent usage figures might be. I live in Sydney and our water storage level is at 79.4%. At 70% our desal plant, which has been in standby mode for yonks, will be switched on.

      • mick

        our sa desal is insurance that cost a bit marshall as late as last week is still ranting about it go figure

  • Graeme Harrison

    Cape Town will be cited as a case-study for how not to do disaster planning. Their authorities are trying to ‘scare’ the population into using less water by claiming that it is only weeks till ‘Day Zero’ when the taps get turned off for 4m residents.

    It would be far better to start implementing the common approach for petrol/gas rationing – the equivalent of odd/even numberplates on odd/even days. They should be turning off major supply valves and pumps, so that each suburban area has pressure in its taps for only one-day-in-three at present. That would force even those profligate users of water to cut-back, saving drinking water in containers for the other two days, and having quick showers one-day-in-three. This ‘time-rationing’ would achieve far greater savings than the current voluntary cut-backs.

    This approach as used when power utilities cannot supply a whole city (‘rolling black-outs’) also gets the citizens used to the rationing. By allowing everyone to have working tap pressure, right up to a day when they go dry – potentially for weeks or months makes people fear the civil unrest likely on Day Zero. It would be better to not have 20,000 people (an average figure) squabbling at each public tap, to get their daily water needs. Keeping them in their homes is always going to be a safer approach, even if that home only has running water (eventually) for one day each week.

  • Bungarra

    So the runoff into Perth’s Dams is not due to ‘Human Caused Climate Change’? There was a discussion re the future of WA’s rainfall at a seminar in 1979 after the huge droughts in the Northern Wheat belt at that time. We were assured that the winter rainfall for Southern WA would decrease as world temperatures rose. The rain belts will move South. We have not yet learned to grow wheat where the rain falls now – in the Southern Ocean. The speakers included CSIRO climatologists. So it has happened.

    This has not been matched by a huge reduction in wheat yields yet as we managed to improve water use efficacy from averaging 25-35% to close to 85-95% in the last 30 years through the adoption minimum tillage systems. (This was achieved using a range of new herbicides. We now have to do it with different systems as the weeds have become resistant to those products. Robotics at the centimeter level, but some plants had become cultivation resistant and hand pulling as well.)

    Now who is advising Canberra’s pollies – the same people ripping the GST out of the West?

  • Tim Forcey

    I was in a home the other day with a showerhead that used 40 litres per minute. And then I was in another home with a showerhead that used 4 litres per minute. This is like “LED vs halogen”, to use an electric-light analogy.

  • Robert Comerford

    Looks like a good time to deepen the dam to be ready when the rains return. Shallow storage wastes a lot of water through evaporation.

  • Shaun

    I like this story, hopefully serves as another piece of evidence towards a wake up call. This sustainability and climate change carry on is a ‘whole system’ thing. Ludicrous to have homes in Australia without water tanks. Greywater use has got to increase. Sadly it’s difficult to see a government acting towards this until a crisis occurs.
    Sydney’s annual rainfall is greater than London, yet stormwater capture is not widely used.
    Greywater use for garden = greater green mass = better colling and shading = reduced electricity for cooling. It’s complicated yet also so so simple.

  • Jon

    It’s very conceivable that this could happen in Australia, we are the driest continent on earth, with a highly variable rainfall pattern and a growing population.
    I find it troubling that it’s still a fairly hard process to get council approval for water harvesting and use in most areas.
    We’re in Brisbane and have just ticked over 4 months with the mains tap turned off. We have 2 of 8,000l tanks and are the planning on installing 2 of 12,000l ones as well.
    It’s very similar to power, it’s pretty easy to store enough to get storage in place for ~75% self sufficiency but much harder to get to 100% self sufficiency. Modeling for a 3 person household (fairly frugal water users, with greyeater) and the driest year on record (repeated for 3 years) shows us needing about 30,000l.

  • dono

    If Cape Towns population had been 2 million instead of 4 million, there would be just a minor crises. If the population had been 5 million – like Sydney – then they would have passed day zero.

  • Humblebee

    GROWTH! Growth is the concept that must change. Growth of cities, growth of economies, population growth. Endless growth is what cancer is and it kills its host. Humanity is the cancer of the planet if we continue with the concept of continuous growth then the same will happen. The planet has been warning us for over 100 years and now it’s screaming. Are we going to listen?

    • Olwen2050

      Yes!!! Thank you, I’m so glad somebody else gets it. I’ve been trying to get that message across but people mostly respond with blank looks. Letters to the Murdoch press – while I’ve had a few published – attract derision from big players like the Property Council. And the minute you advocate cutting back immigration your opponents play the racist card. It makes me feel like there’s no hope.