Jim Salinger’s spending the summer at the University of Tasmania in Hobart. This reflection on the lessons of Australia’s recent floods first ran in the Waikato Times at the beginning of the month, but I felt it deserved a wider audience and so with Jim’s permission reproduce it here.
As I watch from my summer roaring forties perch in Hobart, Tasmania the somewhat unprecedented rains that are deluging parts of Australia raise some pertinent lessons on climate and risk management for New Zealand. Firstly let’s look at some figures and ask the question of what are the climate mechanisms behind the deluges.
For December 2010 the Bureau of Meteorology figures show that eastern Australia (the states of Queensland, New South Wales, Victoria and Tasmania) had its wettest December on record, with an average area total of 167 mm (132% above normal). What caused Brisbane to flood were the heavy falls to the north and west between 10-12 January with totals for the three days exceeding 200 mm. In Toowoomba over 100 mm fell in less than an hour.
Further south in Victoria heavy rainfall and flash flooding occurred between 10 to 15 January, with more than 100 mm of rain across two thirds of the state. Bureau of Meteorology figures show many weather stations in Victoria have now broken their all-time January records in over 100 years of observationd: 259 mm fell on Dunolly (the previous record was 123 mm), and the 282 mm of rain that fell in 1 day at Faimouth in the north east of Tasmania – the highest 1-day total for any gauge on record for the state.
The extremely wet December had eastern Australia primed for the record floods that were to follow in January. The soil could not take any more moisture and the heavy rains turned into runoff, with record floods in some parts.
The causes of these floods have been laid at the feet of the La Niña climate pattern – the sister of El Niño. La Niña brings strengthened moisture-laden easterly winds on to the Australian continent. This year the La Niña event is strong, with it being amongst the top three in magnitude, ranking with the 1918/19 and 1973/74 events. However there is one distinct difference this season: temperatures in Australia this past decade have been 0.5 deg C warmer than in the 1970s, and 0.9 deg C warmer than in the 1910s, all as a result of global warming. And during the 2010/11 season, La Niña seas off eastern Australia have been much warmer than average, being 1 to 2 deg C above the 1985-1998 average.
It is a simple law of physics that a warmer atmosphere holds more moisture. With the long term heating of the oceans more moisture has been measured in the atmosphere during the last decade. The consequence is that global warming leads to an increase in the magnitude and incidence of heavy rainfall, and the resultant floods.
Global warming has arrived, and the climate has warmed. Global warming is no longer a theory…
The first lesson from the Australian flooding events is that global warming has arrived, and the climate has warmed. Global warming is no longer a theory based on abstract calculations of what the climate is very likely to do in future decades. In 2007 the Intergovernmental Panel on Climate Change (IPCC) concluded that “It is very likely that hot extremes, heat waves and heavy precipitation events will continue to become more frequent.”
The second lesson — the canary in the coal mine — is that because of global warming the frequency of these extreme weather events is only going to increase. Thus the one in 100 year high rainfall event will become far more common, with highest-ever totals being exceeded more and more often in the future.
The third lesson is that there needs to be better preparation for these events by civil society. The responsibility in New Zealand falls on local bodies through the Civil Defence and Emergency Management Act (CDEM). It’s local government that is responsible for district plans and granting developers the permission to build. Firstly should major towns be located on river floodplains? This is where there is pressure from developers. A solution is to build higher and higher flood levees but should the cost be borne by the community? Perhaps the full costs should be placed on the developer. Another option is to ban development in flood-prone areas.
However New Zealand is the lucky country in regard to the fourth lesson. We have an Earthquake Commission that covers citizens for flood damage, which Australia does not have. But insurance should be compulsory for all dwellings, to share the cost of these disasters between all citizens.
Global warming is here, now — and not a phenomenon for future generations to deal with. Thus we must embark on a course of emissions reductions targets as soon as possible, to claw back rapidly rising greenhouse gas levels in the atmosphere. If we do not act now the severity of such floods, and the subsequent loss of life and property — let alone the effect on the economy — will increase dramatically. There is no time like the present to invest in our future wellbeing.
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