Queensland floods

The flash flooding in Toowoomba seen on the news last night provided riveting images.

See also Jim Belshaw’s blog. Jim beat me to it this morning.

Jim also had a post on Friday on the wet spell generally.

…During the long drought, I argued that some of the reactions to the drought in the big metropolitan centres in the east were plain silly.

Popular perceptions equated the drought to climate change. Politicians responded with rhetoric, controls and expensive initiatives that confused responses to a long term problem (climate change) with responses to a normal cyclical problem (Australia’s droughts and flooding rains).

Now that the flooding rains have arrived in many parts of the country, I suspect that the risk lies in the opposite direction. Just because we now have water does not mean that problems associated with the weather cycle, with conflicts over water use and with climate change have gone away. I think that a bit more analysis, a bit less rhetoric, would benefit us all!

Jim is right to say popular perceptions “equated the drought to climate change”. I think the scientists, particularly the climate scientists as distinct from popularisers, were more circumspect. Similarly now. As this BOM page shows, there are regular patterns at work:

Click to enlarge.

Water, or the lack of it, has always imposed major restrictions on where Australians live and the activities they pursue.

While drought remains the main scourge for most of the country, there are times when too much water can also have devastating results. Few parts of the country are immune from flooding, whether it be localized flash flooding from intense thunderstorms, or more widespread and longer-lived inundations resulting from heavy rain over the catchments of established river systems. Then normally quiet-flowing streams can spill out over thousands of square kilometres of surrounding country. On such occasions lives can be lost, stock losses may be in the tens of thousands, and damage to homes, businesses, roads, public utilities, property and equipment can run into hundreds of millions of dollars. Lost production can add considerably to the costs, as can the intangible costs, such as effects on health, which are difficult to measure, but significant nonetheless. Overall, flooding is Australia’s costliest form of natural disaster, with losses estimated at over $A400 million a year. On the positive side, floods have some beneficial aspects, such as cleansing excess salt from the soil, washing away man-made chemicals, recharging underground aquifers, and – more spectacularly – causing the desert to bloom.

Tropical flooding

In northern Australia, most of the big floods occur in summer or early autumn in association with tropical cyclones or intense monsoonal depressions. These systems can produce staggering quantities of rainfall – as much as 1,000 millimetres in a few days. The official 24 hour rainfall record of 907mm was set on 3 February 1893 at Crohamhurst, northwest of Brisbane, causing devastating floods in Brisbane. However in January 1979, tropical cyclone “Peter” dumped 1,947mm in 48 hours at Bellenden Ker in North Queensland, as uplift of moisture-laden cyclonic winds by mountainous terrain further intensified already excessive precipitation. More recently (February 1999) cyclone “Rona” produced 1,870mm in 48 hours at the same location.

Flooding outside the tropics

Outside the tropics, coastal areas of eastern Australia mostly receive their flood rains from so-called “east coast lows” that develop from time to time over the adjacent Tasman Sea. Elsewhere in the southern states, flooding is mostly a winter-spring phenomenon, associated with unusually frequent or active extratropical depressions and fronts. However some major events have occurred in the summer half-year as systems of tropical origin extend or move south. Flooding over inland areas is usually associated with southward-moving tropical systems, but in the cooler months, may occur when well developed cloudbands extend across the interior from the oceans north and northwest of Australia. However some inland floods, notably those of Lake Eyre, may be initiated by rain falling many hundreds of kilometres away, and the flood peak may take months to move down-river into the interior.

Flooding and La Niña/El Niño

Flooding, unlike drought, is often quite localized, and therefore not as closely tied to broad-scale controls like the El Niño-Southern Oscillation phenomenon. However the La Niña years of 1916, 1917, 1950, 1954 through 1956, and 1973 through 1975, were accompanied by some of the worst and most widespread flooding this century. It can safely be said that, over much of Australia, flooding is more likely than usual during La Niña years, and less likely in El Niño years, though heavy rain and flooding often accompany the breakdown of El Niño in late summer or autumn.

Any attribution of a local weather event to climate change has to be tentative as climate science deals in longer time periods, conventionally thirty years. Nonetheless, given climate change one must wonder how established patterns such as El Nino/La Nina may be being affected. As parts of the world climate pattern they must partake in the overall change. The common view that climate change will produce more extreme weather events does resonate, but one still must not be too assertive about it.

Queensland is bad. Some of it seems unprecedented. Mind you, it pales in comparison, in human terms, with the Pakistan floods or the Haiti earthquake. (No, Kevin, earthquakes aren’t caused by global warming!)

5 hours later

Things have got much worse since I posted this. Brisbane is under threat.

North coast NSW is also shaping up for bad flooding.

On the other side of Australia:

2 hours on

It is now expected that Brisbane will exceed the 1974 flood level, despite the Wivenhoe Dam having been built after 1974 to prevent such a situation occurring again.

Some are now saying this could become the worst flood in Australia’s recorded history.

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6 thoughts on “Queensland floods

  1. I grew up on the Far North Coast of NSW, spending 20 years there. We had major floods (eg 1974); we had sub-tropical storms during summer. The cyclones were predictable, as were the storms. We knew where they would come from, we knew their physical behaviour, we knew their characteristics.

    5-10 minute violent weather episodes were unknown. They are now commonplace.

    An ‘inland tsunami’ in Toowoomba? Unthinkable back then.

    We’ve just been delayed by 4 days getting out of Boston by a bizarre snow storm. NYC copped the worst of it, its worst such episode ever.

    8m wall of water in the Lockyer Valley? Give thought to the volume of water needed to produce that effect.

    Something is going on with our climate, for sure. I froze at the Anzac Day Dawn Service in my old home town of Lismore, NSW in the late 50s. I could now attend the Dawn Service there in t shirt, shorts and scuffs. Something has happened to cause that change.

    Weird shit.

  2. Yet another perspective might come from the South Australians – starved of water by the upstream dams and weirs along the Murray/Darling catchments.

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