Australian Maximum Temperatures 1910-2010

Ken Stewart, March 2011

In this analysis I have looked at maximum temperatures across Australia including 2010.  Why Maximum temperature?  Well, that’s the temperature we talk about when we think of how hot it was today.  As well, maxima should be least affected by Urban Heat Island effect, and should respond to El Nino/ La Nina conditions.

Before I go any further, let me agree once and for all that 2001-2010 was definitely the warmest decade we have records for.

So, here is an alternative analysis of Australia wide temperatures- with a few surprises.

My data source was the raw maxima for the 100 non-urban High Quality sites, and from other nearby sites when  records needed to be combined (typically up to 20 km away, sometimes up to 35km)  as published at Climate Data on the BOM website.  I later included data from the 34 Urban sites as well.

I used the original (and much stricter) criteria of Torok and Nichols (1996) and only used stations with at least 80 years of data,  and similarly Della-Marta et al.’s requirement to have stations with at least 1 year of data overlap if it was necessary to combine records into a splice.  Consequently, a lot of sites were excluded (29 non-urban, 5 urban) because they did not have enough data, or because no true comparison could be made between modern and historical data.  What remains is a better quality record but which still is less than perfect.

A surprising number of sites had no 2010 data yet, because 1 or 2 months (usually December) had data not yet quality controlled ( over two months later).  Possibly the lower than usual temperatures flagged a warning that manual checking was needed.  I estimated annual data by finding the average of daily maxima for the whole year.

What’s With W.A.?

It quickly became apparent that West Australia behaves differently to eastern states.

This may be partly due to the data bug in WA data discovered by Chris Gilham and apparently not yet fixed.

Or perhaps we should regard West Australia as having a completely different climate system.

Certainly West Australia is not affected as much by the La Nina/ El Nino effects.

Here are the results.

71 Non-urban sites Anomalies, all of Australia:

Notice- the cool years 1917 and 1956; the shifts up about every 20-25 years; 2010 was cooler than any year since 2000, but still  0.11C above the 1961-1990 average.  The 101 year trend is  about 0.65C .

Here is BOM’s time-series graph of maximum anomalies:

Note 2010 is below the 1961-90 average.  My figures don’t agree with this probably because of the sites I excluded because of poor data.  The trend is similar- 0.7C.

East vs West

But look at this:- Non – urban sites excluding WA:Notice that the 2010 anomaly is now -0.22C, and that 1956 is cooler than 1917.

WA alone:

Wow!  2010 was definitely very hot in WA- anomaly of +1.04, just pipping 1994.  And 1968 is only just warmer than 1917.

City vs Country

Now include Urban sites in the mix- in fact, all Australian sites, urban and non-urban (  100 sites).  I should point out that I swapped Melbourne’s Moorabin Airport for Melbourne Regional Office to avoid UHI.

Note the step ups in climate, and a trend of about 0.5C.
Now excluding Western Australia:

Finally, here are the graphs for Urban sites only- remember, BOM excludes these from their climate analyses because of their urban warming signal.

Hmmm… as we’ve seen before, urban sites are warming less than non-urban- in fact hardly at all (less than 0.2C).  And apart from 1956, not greatly different to non-urban.  2010 anomaly 0.12 compared to 0.11.

Beach vs Bush

Now, here is a comparison of coastal versus inland ( more than 50km  from the coast) sites:  

Coastal sites (0.65) are warming faster than inland (0.35), inland sites fluctuate up and down more violently, and inland sites were much cooler in 2010.

Conclusion:

2010 was definitely not a warm year.  Rain and cloud were associated with cooler temperatures in inland Australia.

Maxima do  not rise steadily, but in a series of step ups about 20 – 25 years apart.

There was a distinct decadal spike beginning in 2002-  coinciding with drought conditions across much of the continent.

The first decade of the 21st Century is definitely the warmest we have records for.

The inclusion of urban sites reduces the trend.

Inland sites are warming less than coastal sites, but also were cooler in 2010.  They are more volatile, warming faster and cooling faster.  Proximity to the sea moderates temperature change.

West Australia has a distinctly different climate from the rest of the country.

There is no reason for the Bureau not to include urban sites in their climate analyses.

The next few years will show whether the warming trend is continuing.