Thursday, October 18, 2007

More rain and no change in drought and flood occurrences due to global warming

Countless times and time again, we are being told that we will be getting more droughts and less rain due to global warming. We've also discussed how the CSIRO website climatechangeinAustralia has looked at devastating trends since 1950.

Apparently, global warming likes to increase rainfall in some places and decrease in others. Who knows why!

But I was strangely interested in why the website only mentions rainfall trends since 1950. Australia has great and accurate rainfall data going back to the start of the 20th century, so why not use these? I'll show you why.

Looking at rainfall patterns from 1900 to 1950 and since 1950 we come across some interesting trends as shown below:

State Av.Pre1950 Av.Post1950 %Increase
TOTAL 3813.3 4174.9 9.5%

NSW 481.2 559.2 16%
NT 486.1 553.0 14%
QLD 586.5 638.3 9%
SA 204.6 233.1 14%
TAS 1110.4 1174.5 6%
VIC 608.6 651.3 7%
WA 335.9 365.5 9%

In the last 57 years, every single state has seen an increase in rainfall compared to the 50 years before this. And Australia wide, we have had a 9.5% increase in rainfall.

Hence, if anything, global warming has meant that we are having increased rainfall in Australia. So does global warming cause more droughts, looks like the complete opposite.

But wait, critics (of the non-critical side) will argue that global warming causes more very heavy rains and more periods of no rain - hence greater rainfall in one particular time (more floods) and more droughts. This of course is not shown in the above table, but lets look at the ABOM's own website to see if this is happening:

This graph shows the number of very heavy precipitation days (mm>30):



Nope doesn't seem to any pattern there. And shown below is the number of consecutive dry days:



Damn! No pattern there either.

So there you have it. There is no evidence at all to suggest that global warming will increase droughts or flooding. But there is evidence that we could be getting more rain, and given the greater need for drinkable rain water...this surely is one major advantage of global warming.

18 comments:

Keyser Soze said...

Very interesting! I assume the pre-1950 stats are correct? If so, they're worth a letter to each of the major Aussie rags who are all running the Global Warming line as if it's beyond doubt.

Jonathan Lowe said...

yes mat the stats are correct. Rain gauges are perhaps the longest and most reliable source of climate.

mbes said...

When I learnt arithmetic, 2007 - 1950 = 57, not 67. Perhaps today the rules of subtraction have changed.

Jonathan Lowe said...

lol typo. thanks mbes, am fixing

Anonymous said...

jonathan,
You might like to start on temperature next - while BOM trend maps show Aust has warmed a little since the early 1900's, they also show that since 1970,
* only a couple of small areas in the Centre have warmed more quickly than in the previous 50 yrs and if you do the sums, those areas must have cooled 1910-1970
* warming has slowed or remained stable over the rest of the contient except that -
* an area of WA about the size of NSW has actually cooled. There have also been small outbreaks of cooling elsewhwere.

Roger

Jonathan Lowe said...

I do know that Northern Western Australia has cooled since 1950, and northern Northern terriroty as remained stable, as well as south west WA and central west WA.

But the remainder of Australia has increased in temperature since 1950, and the majority of Australia has increased in temperature since 1910.

This is based on max and min temperatures.

Anonymous said...

Jonathan, I think that clime for each area is controled by it´s enviroment, I mean if you have some mountains they act as barriers so you can not expect a great change in weather because global warming and if you have flat land the clime will not change because the area itself as well as for the case with mountains, weather is controlled by the pattern of prevailing winds and ocean currents; of course with global warming we have more water vapor all around the globe, so we will have more and more heavy rain as the global temperature increases but rain is falling over the same areas (I mean that have not changed its enviroment for the las decades) so if it´s a desert rain will increase a little and if it´s a valley rain will also increase. You can expect much more or maybe less rain only if you change the enviroment.
By the way, I want to as you something: in your opinion what factors produce rain intensity. Please send me an email to solojf@servidor.unam.mx
Best regards
J. F. Solorzano Palomares

Jonathan Lowe said...

Hi J. F. Solorzano Palomare,
thanks for your reply. I am a statistician and not a climatologist, so I can't answer your question, however what I can do is prove statistically that we are not experiencing more drought and less rain, we are not experiencing more floods, and less dry patches as is suggested.

All you need to do is go to the stats to find these things out.

Alan Hunter said...

Mate you must be blind if you can't see a flatening in your graph in the last 10 years, previous years have great flucuations, the last 10 very small flucuations.See my post Jennifer Marhossay's blog re graphs.
What this meaningless graph doesn't show is which month the rain falls, in the Murray region if all the rain falls in the summer it is useless, worse than useless most of the time because crops and pasture don't grow in summer only weeds. we need rain in autumn, winter and spring.
We haven't had an autumn break for 15 yrs, we rarely get enough in winter and spring has become very very dodgy. You might also note that the period 35-45 had unders and overs, from 2000 on its all under and the previous years when it was over I bet that rain fell mostly in summer
If you want to fool somebody use a graph, that is a well known fact in the field of statistics and probability, in fact whole books have been written on this subject, it all depends on the presentation and this one omits the most relevant information, and is therefore useless and a rather suspect was formulated for a different purpose that this blogger has used it for.
To base ones argument on one graph is an exercise in fooling fools.

Jonathan Lowe said...

Hi Allen,
please see this address which shows the rainfall for the murray darling basin. Rainfall has been down in autumn, but spring, winter and (useless) summer have been normal.

In fact when we look at rainfall from 100 to 1950 in comparison from 1950 to today we see that in all seasons we have got more or equal amount of rainfall. The figures are given below:

Average rainfall pre 1950: 449.9
Average rainfall post 1950: 477.3

Summer pre 1950: 126.5
Summer post 1950: 142.6

Autumn pre 1950: 103.3
Autumn post 1950: 105.2

Winter pre 1950: 111.9
Winter post 1950: 111.2

Spring pre 1950: 108.6
Spring post 1950: 117.4

Your ignorance of statistics tells me that you are not scientifically minded at all. If you are not going to back up your stance with statistical analysis, what are you going to back it up with? Opinion?

Alan Hunter said...

Ah Jonathan Jonathan. You accused me of being non scientific yet you can't even get my name right. Like I said if you want to fool fools use a graph (in your case statistics). I have studied the graphs and most show marked changes since 2000, using 1950 as a reference is meaningless try using 2000 it would be far more relevant. In the area where I live (Albury Region) the information I have used is correct. However using the whole of the MDB is utterly ridiculous, there are so many different types of weather patterns and rainfall over such a vast area, that wildly fluctuated up until the last 10 years then flattened out.
It is absolutely useless lumping the Snowy Mountains in the same basket as the southwest Qld, the first has a reasonably stable runoff and the latter goes from flood to famine without rhyme or reason, indeed where I live the average rainfall varies by the kilometre, the further west you go the drier it gets.
I would suggest you study the graphs properly and and you will see I am right.
A more accurate method would be to select a small area with a stable past and then compare the change since 2000. The MDB is not stable it varies wildly from year to year or did till 2000.

Alan Hunter said...

The silence is deafening.
I looked further into your graphs Jonny and I found Annual Mean Temperature Anomaly Australia, it shows above mean temperature for the last 30 years out of 100, I also found lots of other graphs that support this. The trouble with you lot is you scurry around in your little graphs and statisics, till you find something to suit your spin then you hold it up as the holy grail, whilst totally ignoring all around you hoping that no one will investigate further.If you need evidence of climate change read the history of the search for the north west passage, in all those years the leads openned once to allow a ship through, quite often ships would be frozen in ice for 2 winters, some abandoned. The last 2summers you can sail through easily without icebreakers.
Then there are the massive chunks of ice breaking off in Antartica, and nearly every glacier in the world is retreating.
Alan Hunter

Alan Hunter said...

Make that 3

Jonathan Lowe said...

Hi Alan, apologies about not getting your name right. If you had read my article it stipulates that the website that I was criticising, climatechangeinaustralia, suggest that since 1950, rainfall has significantly decreased. Hence that is the reason why I chose the date 1950, as an answer to their comment, not simply because I made up a random year that I thought would better suit my purposes.

Graphs are actually a way to visually show data for easy recognition. It is a widely used technique in all science, and if you want to state that graphs are for fools, then I gather you are claiming that almost all scientists are fools.

As for the month of the rainfall, whilst rainfall in the murray darling basin has increased since 1900 over time , you are right that autumn levels have decreased. However winter levels have stayed level, and spring and summer levels have increased.

If you don’t want to use graphs to state your claim, and you have yet to use data, then I presume you are merely basing your opinion on gut feel. In science, if we want to determine if rainfall levels have increased or decreased over time in certain areas, in certain months and if this rate of increase is statistically significant, then we use data, we visualise this with graphs, and we test this with statistical tests of significance.

Try not to accuse me of manipulating graphs to suit my needs. If you had read by blog you will know that I acknowledge that maximum and minimum temperatures in Australia have indeed increased rapidly in the last 100 years. I never said anything different, and as for the north/south passage, try looking here which shows the global sea ice levels since 1979. Indeed since 2003 it has been decreasing and is more variable – no doubt due to the increases in temperature that the world has seen.

If you thought that I thought that climate change was not happening and that I believe the world is not heating up, then you are completely wrong. I think you have misinterpreted me here, and might well have also failed to read specific articles in my blog.

Although meaningless, I’m not sure how funny this quote of yours actually is: “Like I said if you want to fool fools use a graph (in your case statistics). I have studied the graphs and most show marked changes since 2000”

Jonathan Lowe said...

forgot the autumn level link
http://reg.bom.gov.au/tmp/cc/rranom.mdb.0305.24759.png

Jonathan Lowe said...

The silence is deafening.

Anonymous said...

Yo johnny! Do you believe that our host here is at his comp 24 hours a day, just dying to respond to your posts?
He has a life, do you?

As to those massive chunks of ice breaking off in Antarctic- they are a tiny pieces of an over-water ice shelf on a peninsula sticking out into warm ocean currents and including an active underwater volcano.

In 50 years, 24,000 square kilometers of ice have broken away from that shelf. Even IF the ice were not slowly being replaced, that amounts to only .173% of the Antarctic Ice Cap, over 50 years.

~Otter

PS- good luck Jonathan, against those type you will need lots for a while yet *g*

Anonymous said...

Hmmm. My apologies, Johnathan. I got you mixed up with alan in my introductory line. But everything I mentioned is correct.

~Otter