Inside Story

The lowdown on South Australia’s high-impact storm

Diary of a Climate Scientist | Assessing the contribution of climate change to the South Australian storms isn’t straightforward

Sarah Perkins-Kirkpatrick 6 October 2016 1025 words

In the loop: police direct traffic in the Adelaide CBD during the blackout on 28 September 2016. David Mariuz/AAP Image

Throughout the last week of September, South Australia was bombarded by some very extreme weather indeed. In what’s considered a one-in-fifty-year event, torrential rain and gale-force winds lashed a swathe of the state’s south. Twin tornadoes were coupled with large hail in Blyth; weekly rainfall totals of 94mm, 103mm and 134mm were recorded at Adelaide, Clare and Mintaro respectively. The cyclone-like low pressure system packed winds of up to 140 kilometres per hour, generating some of the strongest airstreams Adelaide has ever experienced. Over 80,000 lightning strikes were recorded across the state.

In some ways, this was a freak of nature. Two strong cold fronts pushed across the southeast on Wednesday 28 September, separated by only a few hours. Over the next twenty-four hours, after a short break in some locations, a cyclone-intensity storm hit the region. The Torrens river, which runs through Adelaide, burst its banks in some locations. Water flooded through the town of Hahndorf after a nearby dam burst its banks, and other rivers – including the Para, Onkaparinga and Gawler – either burst their banks or came very close to it.

These storms didn’t come out of the blue. The Bureau of Meteorology issued detailed, up-to-date forecasts, complete with severe weather warnings making the threat absolutely clear. The forecasts gave time for a degree of preparation. Massive sandbagging operations were carried out to minimise the impact of rapidly rising flood waters, and residents had time to stock up on food and plan work and other travel arrangements. But this wasn’t enough to avoid many severe effects.

The Barossa Valley, famous for producing some of Australia’s best wines, was inundated. Wine growers were hopeful that damage to the grapes would be minimal if floodwaters receded quickly. Roads were damaged by the sheer volume of water, and the cyclone-scale winds brought down trees that damaged houses, roadways and community infrastructure.

Of course, the most widely discussed impact was the complete loss of power across the state, which lasted until the early hours of the next morning. No fewer than twenty-two transmission pylons were damaged, making energy transition impossible., and there were predictable knock-on impacts. The commute home in Adelaide on 28 September was almost impossible thanks to no public transport and blacked-out traffic lights. And, tragically, a number of IVF embryos were lost at Flinders Fertility when backup power systems also failed.

One issue people have already raised with my colleagues and me is the role of climate change in this event. Some scientists have already argued that the role of human influence is clear. But while there are indications that storms and cyclones will become more frequent and intense, at this early stage it is difficult to be confident that climate change was a factor.

The potential increase in storm intensity is embedded in the extra energy warmer air and water holds. The heat capacity of water is greater than air, and storms that feed off warmer ocean waters have a greater likelihood of being stronger. Warmer air also holds more moisture, thus storing more energy that can be released explosively during a storm. Cold front–causing storms may also become stronger: when the front undercuts warm moist air, massive amounts of energy are released as water vapour in the rising warm air, which becomes liquid as it cools.

But the question of how greatly the intensity of storms will increase, and which regions will be most affected, isn’t straightforward. Partly, this reflects the inability of some of our climate models to replicate the scale on which storms and cyclones occur, and partly it’s the result of a lack of standardised long-term observation of cyclones and storms across the globe.

One possible way of calculating the human contribution to wild weather is a detection and attribution study. This analysis compares the frequency of certain attributes of an extreme event using two sets of physical climate model simulations – one under the influence of anthropogenic greenhouse gas emissions and one not. If the frequency is relatively higher in the former, then it is safe to conclude that climate change played a role.

The method is relatively simple, but it takes time and a large investment of resources to develop model simulations using separate analyses for each extreme event. It will be a while before such studies are undertaken for the recent South Australian storms. Until then, it is difficult for scientists to confidently attribute a role to anthropogenic climate change.

The political interest in these storms is hardly surprising. The complete outage of South Australian power is concerning, to say the least, though many conservative politicians have been quick to blame it on the state’s reliance on renewable energy. But it is little more than wild speculation to argue that moving towards renewables increases the vulnerability of the network to extreme weather. The sheer number of pylons that were damaged means that energy supply would have been inhibited, no matter what the source was.

Moreover, South Australia is normally connected to the Victorian network at two main points. Media reports state that one of these connectors was down for maintenance when the wild weather struck, and once the second connection was damaged the SA network was isolated. The competence of the network was compromised by the rare, extreme weather, not by the source of power. Politically, perhaps more energy (pun intended) should be spent on upgrading power transmission rather than clutching at a new way of defaming renewable energy.

The future of South Australia’s, and indeed the whole country’s, energy network should be under scrutiny. An increase in various types of extreme weather will place strain on demand and supply, as we have previously seen in other Australian networks. The conundrum is that our reliance on fossil fuels has been a large contributor to these strains. The damage that the South Australian storms caused should not be used as an advertisement for the “little black rock,” but rather as an example of the fragility of our infrastructure when extreme weather events do occur. •