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Australian Floods

April 6, 2021

By Paul Homewood



Floods in Australia made big news last month, (Click on link to watch video):






The floods mainly affected NSW and SE Queensland. The video talks of “less than 1%” chance of this amount of rainfall occurring. But the BOM figures don’t support this claim.

In NSW, although it was the second wettest March, it was considerably wetter in 1956. Moreover it was not particularly wet in February, so the ground would not have been saturated.

 March Rainfall - Total for New South Wales/ACT



 February Rainfall - Anomaly for New South Wales/ACT


March of course is only one month. Last month 136mm fell in NSW, but this amount is not unusual when all months are taken into account. Indeed it would appear that extreme rainfall months were more common in the past:



The BOM published a summary last week, which highlights various daily and monthly records set at some locations, but again these are only for March. None of this supports the allegation of a 1 in 100 year event. Instead it was just an unusual and localised occurrence for the month of March.






As the video points out, Australia is a land of flood and drought: 


I mentioned March 1956, but that year it barely stopped raining from February to May, which led to the worst flooding in NSW, Victoria and South Australia since 1870. This truly was an epic event, and was accurately described as a 1 in 100 year occurrence. This year’s floods don’t go anywhere near approaching 1956, as the following video vividly shows.

It is 16 minutes long, but I would thoroughly recommend watching it. It not only gives an idea just how bad the flooding was, but also offers an insight into life in those days. Below it is a short film, which also shows how widespread the flooding was. 


Towards the end, you will see a reference to the floods of 1870, which by all accounts were even worse.

The term 1 in 100 year event is regularly abused nowadays, and is invariably used to describe what are no more than common weather events. Scientists doing this belittle the truly epic events of the past.

  1. mothcatcher permalink
    April 6, 2021 8:03 pm

    ” as big as two European countries”.

    Does it mention which ones? France and Spain? or Liechtenstein and Andorra?

  2. Duker permalink
    April 6, 2021 8:31 pm

    Good story. News storeys like the above and even recollections from people still living in the areas can remember even bigger floods.
    While a ‘ 1 in 100 years flood’ can and does happen more often than the time period covered, this isnt a problem as it really means a 1% chance ‘every year’. But once you get around the 2% level the amount of extra rainfall to become a 1% event is quite small as well as not completely accurately known.
    NSW is of course nearly 1/3 bigger again than France and can have quite different climate zones and what is an extreme weekly rainfall in one area is quite common in another

  3. April 6, 2021 9:37 pm

    A 1% event, what does that mean? Do we possess enough records to say reliably what is a 1 in 100 year rainfall event for this part of Australia.

    However somebody has to decide what this is, before the flood modeller can have a go at predicting what the 1 in 100 model flood outline looks like.

    Then you get into really boring stuff like “Integrated Hydrological Digital Terrain Models” which model the catchments and watercourses, then somebody does a statistical calculation of how much water goes into the puddle, then a hydrograph is created using the latest statistical techniques, and then the model churns out some pretty pictures of the puddle and flood outlines for 1 in100 year events and even 1 in 1000 year events etc. (how do they know!)

    At this point reality should intervene and the model flood outlines should be calibrated against known flood events, flood levels, any measurements or even pictures, and an iterative adjustment process should take place. But as this last bit is even more boring than the first bit it usually remains in the “just too f*ing hard box”

    The flooding in the lower part of our village regularly exceeds the 1 in 1000 year model flood outline and we have 25 years of auto gauging records that the EA have used to calibrate the hydrograph.

    Does this mean we are suffering from effects of climate change, there are many who say we are, but the EA remain silent as they know that flood modelling contains a lot of uncertainty.

    Do we (the residents know) what is the cause, well of course we do, we can read the history of our village back to the Domesday book and flooding has always been a problem. In modern terms we suffer from “Groundwater Flooding in a shallow unconsolidated aquifer setting” (ancient river terrace sand and gravel deposits) and none of the industry standard flood models includes this mechanism, as it is happening out of sight underground.

    • April 7, 2021 8:59 am

      The term ” 100 year event “is certainly abused now…for proffit. In the oil industry statistically wave hights to which installations must conform are given as 10, 20 30, 40 50 etc. That does not mean you must wait that many years for the event…after all when is time zero. Also as this is simply statistics it does not prevent two 100 yeare events occuring in the same year. It is only “unlikely” not impossible. Also the weasels in the IPCC arbitarily changed the plucked out of the sky number for minimum period for units of climate change from 50 years to 30 years. Now! Each of those becomes a single data point. Who except someone playing fast and lose with the term dares to talk about a trend containing less then three points and even with 3 points ( 90 years) you are shooting from the hip. Lies, damned lies and statistics.

  4. Solon permalink
    April 6, 2021 10:41 pm

    Apparently Japan is blossoming the earliest ever this year. “Experts” aren’t sure whether it should be blamed on climate change or covid….

  5. Mack permalink
    April 6, 2021 11:35 pm

    In her famous 1908 poem ‘My Country’ (infamous probably, to climate alarmists) did not Aussie settler Dorothea Mackellar describe a land of ‘drought and flooding rains’ and, more so than drought, insist that ‘floods’ would never break her will? What on earth could have caused all of those beastly floods in the early Edwardian era in Australia when co2 was still at pre-industrial levels?

  6. Graeme No.3 permalink
    April 7, 2021 12:01 am

    The east coast from northern Queensland down to just below the NSW/Victoria border have had floods. A stationary high (southern hemisphere cyclonic) with a low (anticyclone) trapped between it and the east coast.
    They didn’t bother mentioning Queensland in the report because they have heavy rain in summer and know about it (and are prepared for it). Northern NSW also gets heavy summer rain (although not this heavy every year) and they mostly know it could happen. The major flood damage will be to those suburbs built on river flats and bought by people who never thought ahead. Also those who built very expensive homes on the edge of cliffs around Sydney and have had the face of the cliff partially washed away under them. As for heavy rain in Sydney I drove home (normally 20 minutes) in October 1986 and made it there in 2 hours and 10 minutes. Many cars were stranded. From memory the same thing happened a year later almost to the day. I wonder what would have happened if I’d owned an Electric.

    The 1956 flood in Mildura and in SA was from heavy rain in Western Queensland and NSW which was carried away by the rivers into the Murray river and down to the sea. I was young then and my parents drove up to Murray Bridge (where they had lived some years before). All the old part of the town was on higher ground and untouched, the local Hotel was just above the flood water, you could sit on the ground floor verandah floor edge and dangle you feet without touching the flood. The ground sloped strongly downward front there and (single story) buildings about 100 feet away from the pub were flooded almost to their gable.

    The talk of a “once in a hundred year flood” is garbage.

  7. Duker permalink
    April 7, 2021 5:07 am

    This good story from Queenslands Chief Scientist about estimating the AEP from data

    He makes the point:
    There is always a level of uncertainty inherent in such analyses. For example, the chance of a flood with a stream flow of 2,200 m3/s (as arrowed, left hand axis) in any year is estimated to be between 1 in 50 (2%) and 1 in 10 (10%). This is said to be ‘within 90% confidence limits’, ..”
    Australian rivers rarely have the flood control works that are common elsewhere and with the shallow gradients in a flat country the flood plains can be vast ( as they once were for say the Thames or the Rhine)

  8. Crowcatcher permalink
    April 7, 2021 6:49 am

    There is a good video o YouTube about The Great Artesian Basin and, of course, these periods of of “heavy” rainfall are necessary for its replenishment, otherwise all those wells in central Australia would very very quickly dry up.

  9. April 7, 2021 7:54 am

    Before the Europeans split the year into their four seasons, Australia had two : the wet and the dry.

  10. martinbrumby permalink
    April 7, 2021 7:56 am

    1 in 100 years?
    Fiddle Faddle.

    UK reservoir spillways are supposed to be capable of passing a 1 in 10,000 years flood.

    Noah would have been proud.

  11. MrGrimNasty permalink
    April 7, 2021 10:14 am

    After a bit of non-laying snow yesterday right on the S.Coast, and a sharp frost, it reminded me of April 2008. There was a surprise overnight snowfall 2″+ laying, probably the 5/6th (my records are a bit messy/confused), and the max. temp was suppressed to only 4C by the melting snow (all gone by evening). We had air frost 5 consecutive days in the range 0 to -3C. It was between -2 and -3C last night.

    • Mike Jackson permalink
      April 7, 2021 11:39 am

      An inch of the stuff lying in south Burgundy this morning — and not in any hurry to move even in the sun. My daughter reported blizzard conditions in Interlaken at 0800!

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