Townsville Rainfall In Context

The rain event which caused massive floods in Townsville (and fearful stock losses in the north-west) has now ended.  There have been some who have made further political capital out of this disaster by linking it to climate change.

According to Independent Australia, a “progressive journal”,

The City of Townsville, with some 20% of its suburban zones under water today (6 February 2019), might now be a model for the world — for possible climate change impacts and handling them. 

These days, the very heavy falls have been happening more frequently — for example, in 2007, 2009 and then in 2010.

Time for a reality check.

This has indeed been a record breaking event for Townsville.  A few graphs will illustrate.  Townsville airport has had its wettest 14 day period since 1941, averaging over 100mm per day.

Fig. 1:  14 day rainfall

Tville 14d rainfall

It has also broken the record for rainfall over 31 days:

Fig. 2:  31 day rainfall

Tville 31d rainfall

And with the wet season far from over, it is very likely to break the 121 day rainfall record.

Fig. 3:  121 day rainfall

Tville 121d rainfall

Townsville’s rain is very seasonal.  Annual rainfall averages about 1127mm, and half of that falls in January and February, with another quarter in December and March, so a plot of 121 day rainfall captures the relative strength of wet seasons over the years.  There doesn’t appear to be any recent increase in wet season strength.  What is interesting is there are periods of wetter and drier years, which is more plainly seen in a plot of decadal rainfall.

 Fig. 4:  Decadal rainfall at Townsville

Tville decadal rainfall

Rainfall appears to be in a decreasing trend.

But what about the claim for greater frequency of very heavy rain events?  Heavy rain events are usually short and intense, so three day rainfall will also show relative frequency and intensity.

Fig. 5:  Three day rainfall

Tville 3d rainfall

The “Night of Noah” in 1998 is obvious, and there was another intense event in 1953.  But there is NO trend.  (The calculated trend is zero.)  Intense events are not more frequent.  Similarly, the number of days per year recording 100mm of rain shows zero trend, even though there have been eight already this year.

Fig. 6:  Count of days per year with over 100mm of rain

Tville days over 100mm

There is no climate change signal in Townsville’s rain record.

Now, to show how different locations can lead to completely different interpretations of trends in climate, I turn to two locations in wetter parts of the tropics that I have some knowledge of.  I lived for many years not far from Pleystowe and Sarina Sugar Mills near Mackay, which are about 30 km apart.  Sarina appears to have an increasing trend in rainfall:

Fig. 7:  Decadal rainfall at Sarina

Sarina decadal rainfall

While Pleystowe shows no trend.

Fig. 8:  Decadal rainfall at Pleystowe

Pleystowe decadal rainfall

Notice the similar patterns of wetter and drier periods in Townsville, Pleystowe, and Sarina.

And incidentally, the most intense and highest rainfall events in these locations occurred many years ago, in 1990-91, the 1970s, the 1950s, and 1918.  As with the recent Townsville flood, these occurred when the monsoon trough, with embedded decaying cyclones, lingered overhead for many days or even weeks.

The Townsville flood was not due to climate change, but to a frequent North Queensland phenomenon- an intense monsoon trough stuck in one place for too long.  This was an unusually intense and long lasting example, but such events are not more frequent or more intense.

Tags: , , , ,

2 Responses to “Townsville Rainfall In Context”

  1. Geoff Sherrington Says:

    In the 1953 rain event my parents owned a “house on high blocks” in Bowen Road. The home is still there, with a shop front added for Lansky Saddlers. Lats & Longs are 19 17 58.38E, 149 57 59.35S.
    One might still be able to see the high marks of flood waters on the house posts about 0.8 metres above the ground. I remember it taking about 3 days, maybe more, to recede. Before 1953, there was another high mark from an earlier flood event, but 1953 was higher.
    It is hard to understand why the logic of building “homes on stilts” there is not as justified now as it was then.
    Sure, a major dam was built on the Ross River after this rain event, but dams have their own management issues in times of heavy rain, as seen at Wivenhoe.
    Consequently, I do not regard the flooding this year as unprecedented. Memory trumps synthesis of past events. Geoff.

  2. John Trigge Says:

    I sent Independent Australia a comment. I hope you do not mind me making reference to your post.

    Your item by Dr Duffield on the Townsville floods hypes climate change as the cause of the recent event. The inference is that he is using the IPCC definition in that climate change is caused only by we humans.

    To reinforce ‘climate change is the cause and we should do something about it’, he posits an increasing incidence of floods, in particular 2007, 2009 and 2010.

    It’s a pity he is such a short-sighted ‘expert’ or he would have also mentioned the many other high rainfall years going back to 1941, many of them higher than the years he mentions (see for an analysis).

    The reference shows that heavy rainfall in Townsville is common, cyclic, certainly an effect of climate change but just as certainly a natural phenomena and not caused by we humans.


Comments are closed.

%d bloggers like this: