The browning of Australia

Reader Proust points me to this helpful BOM site showing rainfall trends in Australia. You can choose your own region, season and time period.

Here’s the most relevant to consideration of the effects of global warming, the trend since 1970, which demonstrates how much drier the climate has become over the period in which warming has been observed. As various people have pointed out, is was even drier during the famous Federation drought at the beginning of C20, so the role of global warming isn’t conclusively established, but it would certainly seem unwise to bet on a rapid return to the average observed in the historical record

Rainfall trend

82 thoughts on “The browning of Australia

  1. Dear Roger

    Thanks – but your comment about SE Australia conflicts with your previous comment on atmospheric circulation, as such a small area is unlikely to have a meaningful relationship between heat and rain however statistically significant your negative correlation may be (what is the t?).

    Regressing your rainfall in SE Australia on mean temperature for the whole country from 1950 to 2005 produces once again a POSITIVE correlation with R2 = .27, X = 0.6, t = 4.5, so statistically significant and in this case climatically meaningful.

    As for that part of the Murray catchment in SE Australia, with average annual rainfall of just 328mm in 1940-1947, against 579 in 1998-2005, I doubt the inflows then were better than over the 8 years before the present, pace JQ.

  2. “perhaps you will have more luck than Ian Castles and myself in getting JQ to agree that as you say “global warming IS (my emphasis) increasing global average rainfallâ€?.”

    If you have ever raised this issue before, TOS, I don’t remember it, and a quick scan of your comments didn’t find it. I have no reason to doubt that global warming is increasing mean global rainfall, and I’ve certainly never said anything different.

    Proust, the arithmetic properties of a moving average are what they are. I didn’t pick 11 years, and it’s bit late for you to say now that it’s too sensitive to one very low year. As for your claims about quartiles, the probability that a single observation picked on an objective basis (in this case, the most recent observation on the moving average) will fall into the bottom quartile of a distribution is exactly 0.25. It’s certainly not 0.35, 0.4 or any other number you want to dream up. Of course if you cherry-pick a particular time period like TOS in the comment immediately above, you can get whatever you like – I assume you had something like this in mind, but it’s inapplicable here.

    Coming back to the main point, if you want to continue the dispute over the conclusion that the weather is, as I said at the start of all this, getting hotter and drier [as we have discovered in the discussion, as a result of higher evaporation as well as lower rainfall], I suggest you move the discussion to the thread on “Drying out”.

  3. Dear TOS,

    I did the correlation but certainly did not assume that temperature drives the relationship. The negative correlation at location is, as I implied, due to local effects only. You left out your domain of analysis in previous posts, hence my quick check.

    Nor am I convinced that your correlation is climatically meaningful. The following paper suggests the correlation of rainfall and max temp over Australia is strongly negative.
    Nicholls, N. ; Lavery, B. ; Frederiksen, C. ; Drosdowsky, W. ; Torok, S. 1996 Recent apparent changes in relationships between the El Niño-Southern Oscillation and Australian rainfall and temperature
    Geophys. Res. Lett. Vol. 23 , No. 23 , p. 3357 (96GL03166)

    I have the Upper Murray inflows to 2000-1. Yes, the forties were low but I am reliably informed by the custodians of the data, that the latest accumulated natural inflows (since 1997) are the lowest on record.

  4. Roger said:

    Global warming is increasing global average rainfall, but recent research by the UK Hadley Centre suggests that rainfall is becoming more spatially variable on a global basis. Harsher droughts, more deluges.

    That is as I understand it. I heard a climatologist explain on the radio that with a higher temperature the saturation point rises. Hence the atmosphere can hold more water. But when something disturbs it there is more up there to fall down.

    I also recall a climatologist saying that we have been experiencing a predominance of large high pressure systems with the lows tracking further south in recent years. This was said to be related to tighter circulation patterns over Antarctica, I think to do with the ozone hole.

    If this is so, it seems to my simple mind that there may be an upside in that the melting of Antarctica may be delayed, apart from the bit that sticks out. But then the sea is majorly in contact with the ice, especially under the large ice shelves, so I expect it will be chewed out eventually.

    And I wonder what impact the 30% reduction in the thermohaline circulation in the North Atlantic in the last 12 years is having on our weather here.

    But I’m wandering…

  5. Quiggin:

    Proust, the arithmetic properties of a moving average are what they are. I didn’t pick 11 years, and it’s bit late for you to say now that it’s too sensitive to one very low year.

    It is a matter of record that you picked 11 years, this is your statement:

    B: Hot, dry weather as observed in the period 1995-2006 occurs [with probability 0.25]

    On this:

    As for your claims about quartiles, the probability that a single observation picked on an objective basis (in this case, the most recent observation on the moving average) will fall into the bottom quartile of a distribution is exactly 0.25.

    Of course.

    Of course if you cherry-pick a particular time period like TOS in the comment immediately above, you can get whatever you like – I assume you had something like this in mind, but it’s inapplicable here.

    At last!! I could not agree more. Cherry-picking is precisely what you are doing, as my analysis of 1995-2005 shows.

    If, as you claim, 2006 will change the 11-year moving average from “unremarkable” to “astonishingly dry”, that tells you 2006 is an extreme outlier. Therefore, ending the timeseries in 2006 and not 2005 is cherry-picking your period (it just happens to be the most recent period, but 1995-2005 is also recent enough for the purpose of this disscussion, as is 1994-2004, 1993-2003, etc – all “unremarkable”).

    It would be one thing if it had been overly dry for the last several years, for then your argument would be relatively insensitive to the chosen period. But it’s not; your argument depends critically on ending in 2006, not 2005. Which means the support for your argument is essentially one data point: 2006.

  6. Proust, making up quotes, as you’ve done above, is usually an indication of desperation.
    Including 2006 shifts the 11-year moving average for rainfall from below-average to well below average.

    More importantly, the discussion has demonstrated quite clearly that hotter, drier weather, including higher evaporation, is leading to flows into catchments that are well below the historical average and, for the Murray-Darling at all-time (historical) lows. This was the original claim disputed by you and Ian. I’ve restated it in “Drying out”, so if you have anything further to say, please do so there.

  7. Which quotes? Everything in blockquote tags is a direct quote of yours. The other quotes (“unremarkable”, “astonishingly dry”) are what is known as “scare quotes”. Look it up. As a general rule I don’t like them – but they slipped through here.

    Including 2006 shifts the 11-year moving average for rainfall from below-average to well below average.

    Yes, strictly speaking 585mm is below-average. But when the average is 600mm +- 100mm, 585mm is not significantly below average (in the statistical sense). So “unremarkable” is a more appropriate description.

    You cherry-picked. Or just applied sloppy statistics, I don’t know which. Then when caught out, you simply shifted the goalposts. But I wouldn’t worry about it, you’re in good company – your approach seems to be the MO amongst many influential climate scientists.

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