Dr David Jones, the head of climate analysis at the Australian Bureau of Meteorology, in an opinion piece, ‘Our hot, dry future’ has argued that over the past 11 years Melbourne’s rainfall has been about 20% below the long-term average experienced declining rainfall over the past 11 years .
In response, Dr Jennifer Marohasy posted ‘How Melbourne’s Climate Has Changed: A reply to Dr David Jones (Part 3)’, which included a graph of high quality data of rainfall at Yan Yean, Victoria, because of its proximity to Melbourne.
The graph is from Mr Warwick Hughes based on Bureau of Meteorology data and shows that recent rainfall decline at Yan Yean is comparable to declines during previous droughts.
I have also graphed Bureau data for some of Melbourne’s catchment areas. While I couldn’t find a site with data extending back as far as the Yan Yean site, the Maroondah and O’Shanneyssy stations show a significant recent decline in rainfall that is greater than previous droughts in the 1896, 1925 and 1945.
Some of the Melbourne catchment areas rainfall data shows recent significant decline, but there are a number of problems with using bureau rainfall data for the Melbourne catchment. A main problem is that the Bureau does not have rainfall data for Melbourne’s largest reservoirs, Upper Yarra and Thomson back more than 30 years.
The best publicly available data on catchment area rainfall comes from Melbourne Water. However, Melbourne Water’s publicly available data is only from 1998 to 2008.
Without long-term high quality data of catchment area rainfall for all catchment areas, it is impossible to know whether the longer-term trend shows dramatic declines at many, or just some, places in the Melbourne catchment.
Nichole Hoskin
Blue Mountains, Australia
Jennifer Marohasy BSc PhD is a critical thinker with expertise in the scientific method.
Thank you, Nichole, for your most informative post. My understanding was that David said that over the past 11 years Melbourne’s rainfall has been about 20% below the long-term average, not that Melbourne had experienced declining rainfall over the past 11 years, which is a different point. Your graphs of rainfall at two reservoirs appear to support the latter point as well – strikingly so in the case of Maroondah.
Nicole – may I suggest you get the raw Yan Yean data in Excel and check against BoM’s decile analysis here. http://www.bom.gov.au/climate/current/statements/scs16.pdf
See what percentile range the period for Oct 2001 to Sep 2008 rainfall is.
And perhaps October 1996 to Sep 2008.
Decile analysis is always good for the soul.
You simply compare the Oct 2001 to Sep 2008 period of 7 years with all other 7 year periods before in the record. Calculate all the seven periods Oct to Sep back in history – should be near 115 odd. Then rank our recent period with respect to the others. (And you have to do the whole period – you must not add yearly deciles – mathematically not on !!).
Sorry should read “seven year periods” and there will only 110 of them (I think … n- (m years-1)). You’ll see it when you do it.
Hey Luke,
What about you getting David Jones to provide us with the data that he used to conclude that the last 11 years are 20 percent below average?
And if you have done the calculations you suggested above for Nichole – why not send in the charts for me to post?
As I pointed out several times.
Dr. David Jones is using the precautionary principle.
It has its advantages…..It’s an attractive stance to take.
He’s “blameless” from most angles. The motivation is clear cut.
“Dammit David! It’s raining and flooding everywhere, and all the catchment dams are full and everyones happy…..a real disappointment!”
Let me know when that happens.
Nichole; thanks for posting this review and the extra rainfall graphs. To complete the picture on Melbourne’s water decline we need a little more info and that’s perhaps still tied up in old MMBW resevoir inflow records. Rainfall gauges don’t give us runoff particularly in drought.
Besides the three sites analised in these threads I suspect records for the Silvan Resevior up in the Dandenong Ranges should go back to the 1930’s when flows from other sources were diverted through this important development. Also tainfall there is most likely covered by BoM records from the Mt Dandenong, Mt Evelyn, Ferntree Gully etc region.
IanC; we have good sources closer to home but I’m only guessing about official rainfall/river flow studies re the National Capital development programs. What we got today, was the ABC story on the fate of certain Anzac Avenue trees where once hardy blue gums have failed after only 40 odd years. I expect to hear many excuses, other than drought, that may be affecting our older trees meantime such as traffic fumes however it all adds up to AGW right under our nose.
Well Jen – I now have a set of Yan Yean data back to January 1889 and this is a preliminary result that I need to check but just so you don’t think I’ve left you and done a runner. Did a hack on 84 month percentiles and 1899 sequence (start year running backwards) beats the 2008 sequence by 4mm over 7 years…. so 2008 is second lowest by a whisker on 113 sets of 84 month sequences.
BoM have standardised on post 1900 for quality reasons some time ago (and we could debate all this) so they would see the Oct 2001- Sep 2008 sequence as worst on record.
Anyway – I’m tired so need to check some more.
But on the 144 month sequence 1996-2008 beats all other comers (1947 sequence closest) by a fair margin, supporting David’s position substantially.
Gavin : don’t know the species of blue gum in Canberra they are probably well out of their beat. Examples such as the Sydney Blue Gum seem to favour reasonably sheltered areas and thrive if they get a good drink . Canberra, I would imagine, is too hot in summer and too cold in winter and not forgetting, too dry generally.
Hi Ian, I’ve made the correction to the quote from David Jones. Thanks,
Luke; I’ve come to the conclusion there is a great deal of information regarding Melbourne water not yet available on the internet and that’s been frustrating my responses on these threads. Having only a limited knowledge of MMBW history is a handicap too it seems.
One thing I recalled overnight is the MMBW works on the Plenty River. There must be rainfall and stream flow records for the Ringwood, Warrandyte and Eltham catchment that go as far back as Yan Yean. Research and Lower Plenty were in the hub of operations during my days there too working out of the Mitcham Depot.
http://www.melbournewater.com.au/content/water/rainfall_data/rainfall_data.asp
Anyone with a decent street map can find Pound Bend Rd and see a diversion tunnel (1870 gold mining) on the Yarra. This guy’s gallery has some good pics of this historic river bend. Perhaps we can estimate the low summer flows back then (wink, wink).
http://web.aanet.com.au/~image//yarra/
WJP: I occasionally relate this yarn in regard to our Blue Gums E. globulus. It is only a vague recollection though from the time when I first became interested in Australian natives. Don’t quote my references!
A long time ago, an enterprising government agency, probably the early CSIRO working through foreign aid programs sent blue gum seeds to Addis Ababa where the locals cultivated them in seed boxes to be sent out later to mountain communities who likewise were preparing their rocky slopes by digging holes with a pick in order to catch some wind blown dust to act as fresh soil.
When the hapless seedlings arrived they were rudely plucked out of their boxes roots and all, and then stabbed into the grit only to be followed by a long hot pee. Needless to say they were soon forgotten but the rest is history.
My own experience with these gums relates mostly to their wild appearance, massive buts, wiry wood and their characteristic bloody mindedness. These most aggressive plants will grow anywhere at the expense of everything else and that’s why I mentioned them in this context.
If they can’t do what they do well, what else can we have, cactus?
For notes on blue gum overseas, see –
http://trees.stanford.edu/ENCYC/EUCglo.htm
“Let me know when that happens.”
You’re perfectly right, SJT, it’s never gonna rain again.
“It all adds up to AGW right under our nose.”
The only conclusion you could possibly draw, Gavin.
Just for the sake of clarity, are we talking about the rainfall for Melbourne ie the urban area or rainfall in the catchments which drain into the various dams that provide Melbourne with its water – the catchment areas are definitely not urban. I suspect the BoM rainfall figures for Melbourne are recorded in the city or close to it. Rainfall in catchment areas may be quite different. Even if there was zero rainfall in the city (most unlikely for Melbourne) the catchment areas could still get sufficient falls to maintain Melbourne’s water supply. My point is that you can’t just interchange Melbourne rainfall figures with catchment figures as if the were the same.
Indigo Jones forecast some 50 years ago that australia’s greatest drought in recorded history would start around 1990. The Bom never has liked educated dissent , Especially when they can’t control empirical observation.
Rossco – type Yan Yean into maps.google.com.au and then do the satellite overlay
or
http://maps.google.com.au/maps?f=q&hl=en&geocode=&q=yan+yean&sll=-26.487734,147.974992&sspn=0.543893,1.057434&g=mitchell&ie=UTF8&ll=-37.68219,145.030518&spn=0.480928,1.057434&t=h&z=11
Gavin,
E. globulus,saligna and territicornis are all “blue gums” and there are probably others.
Anyway, do you know what killed them?
There are lots of eucalyptus diseases and infestations.
Probably someone from Queensland with phytophthera on his tyres.
Actually the US is a good source of info on eucalypt problems.
“But on the 144 month sequence 1996-2008 beats all other comers (1947 sequence closest) by a fair margin, supporting David’s position substantially.”
If we look at the sub tropical ridge/ high pressure belt, we find a similar pattern.
The intensity of the subtropical ridge previously peaked in the 1940s at the time of a
particularly dry decade in the south-east (South-Eastern Australia Climate Initiative).
So this is a historical pattern. Why would we bother keeping records if they didn’t change?
There is nothing wrong with change. Yes it’s very dry, but you wait. Just as all the records are broken regarding low rainfall and high temperatures….really…the good doctor should know better. It’s going to flood so hard, and rain and rain and rain.
IT WILL BREAK ALL THE RECORDS (There are thousands of hectares of floodplain that has never had a flood!)
Some people, even “experts”, find it hard to come to grips with drought.
It’s one thing to talk about drought……but to live through it and experience it, is another..
How far outside the standard deviation is 1996-2008 for the entire data set?
Having a 50 year gap between two low points doesn’t suggest a trend. How does that support David’s position “substantially” ? What am I missing here? Is there a detectable down trend?
Well 1996-2008 is the lowest sequence in 119 years. Lowest on record. Is there a trend? Look at the end of the graph.
As for the STR – the comment from Timbal (2008) is “On a century timescale,
it appears that the evolution of the ridge intensity follows closely the global
warming of the earth’s surface, with the rise in the ridge intensity since the 1970s
explaining up to 80% of the rainfall decline in the east and potentially also explaining the
further reduction in the west that has occurred since the mid-1990s.”
On century time scales the Walker circulation has also weakened considerably. (Smith and Power 2007).
There’s a whole lot more going on.
Will it rain again – of course – but that’s not the question – how long till the next drought is the issue. Frequency.
Very good STR Luke. So what does that say about global warming and the land of drought and flooding rains. We need the cooling for the historic rain events, but would it rain without the warming to begin with? The key to the future is the past.
Frequency?
Thats what drought is. Consecutive years of below the average. Now we wait for the above average consecutive years.
What we consider “normal or static” will change. As always we gain a new perspective.
What would you say about global cooling? I’m sure you wouldn’t be impressed. But sadly, it’s either one or the other…above average or below average…..consecutively.
Luke; your map link also shows the Lower Plenty River mentioned above, and Pound Bend by the Research – Warrandyte Rd. As I said before, there must be long term rainfall & stream flow records from this neck of the woods too.
Rossco; this area is like Yan Yean, part of the old MMBW system. Water from the Plenty River was diverted into the urban supply and its impact has been the subject of recent catchments management inquiries. At one low point in summer supply during the 1970’s we were preparing to divert and treat the muddy Lower Yarra water below Warrandyte too.
Spangled: “The only conclusion you could possibly draw”, forgive me if you can but I have many interests in retirement. Today I managed to make an important phone call to a stranger regarding a recent 4 Corners program in between recycling some old hammer handles.
I do a lot of estimating re the remaining strength in an abused piece of dried out wood these days. Knowing the local hardwoods found in typical hardware shops over the ages helps as does the art of cheating with the actual fitting. Modern OH&S gurus would be horrified hey.
Experience helps in other matters too. About a decade before I was fitted into MMBW instrument maintenance teams commissioning new projects an old guy from Preston I worked for briefly landed a big fish in his back yard. A rather desperate gang of Melbourne City council workers hastily dug up an ancient bronze water meter from under the cobblestones and tram tracks in down town Sydney Rd. They delivered the whole thing on the back of a truck to Ernie’s home drive way one sunny afternoon so I got the enviable job of fixing and calibrating it while police directed peak hour traffic round their giant hole. Lets say they were there for some hours.
This instrument monitored water from Yan Yean. I recall someone agreed to put it back next day after the professors up the road reckoned it had a 6% range error on top of a sluggish start up on low flows after testings overnight. I guess Melbourne waters users got the benefit of the doubt for quite sometime after that episode however there were thousands of other meters round town besides their pivotal main line monster.
This is where back up systems come into play with our estimations. The only way they knew they had a problem other than an old miniature turbine in a bypass with half it blades missing was lots of home work back in the office. By purely statistical methods the experts reckoned they had a giant leak or possibly a rouge customer with a big appetite for free water but systems can’t be wrong can they?
The reason we got that job? that big industry by the road was also our customer with their large numbers of yardage counters. Flexibility in the job is also a handy tool.
Assessment in all measurement is about recognising magnitudes. Start points and end points are not so critical but the finished job depends somewhat on attitudes as well as application. I learned a long time ago to depend more on practical experience than pure calculations. Quite often it must include others as it’s teamwork that can save the day. I read a lot about such spirit from contributors to this blog
“The key to the future is the past”
Thats hardly mainstream sceptic rhetoric when it comes to GCM’s hey
“I learned a long time ago to depend more on practical experience than pure calculations.”
Gavin,
You sound like you are a sceptic at heart.
Spangled
Nichole claims “Without long-term high quality data of catchment area rainfall for all catchment areas, it is impossible to know whether the longer-term trend shows dramatic declines at many, or just some, places in the Melbourne catchment” ,
whereas I know from experience this part of our country is perhaps the most studied area on the planet in terms of it’s climate and hydrology. We can expect the records to be much deeper than those served up on a plate by Melbourne Water.
I was certain Jennifer too was taking a big risk with the earlier threads in response to David’s letter in the newspaper. Sure, there is always another angle to approach a problem but one has to wonder why we use this or that method.
With a bit of hind sight things like crafting hammer handles can help. This I guess is where we leave IanC, perhaps a few others behind.
In the wood trades there are basic concepts like working with or against the grain and it’s one of the reasons I take more than a passing interest in old eucalypts.
There are many reasons why trees and handles made from their wood fail. I noticed last week a big specimine by our new library that rolled overnight in the wind had whiteish masses under the trunk instead of the usual shattered roots. However I often refer to the issue of self sown v overgrown pot bound native seedlings used in plantations in their early adaptation to hard baked ground. Roots can strangle each other at ground level as the later specimines mature.
Back to hammers; with the 4 oz size the wood behind the head is rather delicate however in the hands of a master craftsman it’s the head that does all the work, not the handle. In physics we learn about action and reaction, impacts and kinetic energy so that handle also becomes my sensor for efficiency.
Heres the rub. After brutally destroying the grain on the wrong side with a blunt plane I can give that cranky bit a quick burn on my bench grinder so the head fitting marks can be more easily seen for the next adjustment. That’s not illegal because I’m also a metal worker by trade.
When it comes to knocking out dents in a polished copper or aluminium vessel of merit and aiming at the crimp line rather than the whole dent it’s the scatter of tiny indentations that add most to the to the final finish. We can’t bog our mistakes here.
Developing a moving average in otherwise quite rigid metal is another craft. Pushing the boundaries of crimps and dents after they have settled becomes a question about perfection in the reflection from the final curve. After years of experiments I’m resigned to dissapointments and so have gained great faith in the experts.
Peer review at this level must involve a mutual understanding of work hardening and acordingly setting limits for the process .
Hi Gavin,
Hi Gavin,
There is data available for Silvan, Yan Yean and some of the other smaller catchment areas. However, these smaller reservoirs are located some distance away from the 4 main catchment areas, Thomson, Upper Yarra, Maroondah and O’Shannessy. I have been told that the climates of the four main reservoirs are similar and that the smaller reservoirs are used mainly for storage of water since they receive less runoff.
I agree with you that the problem is that Melbourne Water doesn’t provide long-term high quality catchment rainfall data publicly. I find it hard to believe that the body entrusted with the responsibility of managing Melbourne’s drinking water doesn’t have long-term catchment rainfall data. That would be incompetent. They need to make that information publicly available to enable an informed debate on whether there are long-term declines in catchment rainfall for some or many reservoirs.
I also think that the data is out there. I wonder why, in a political climate where water is a key issue, this data isn’t publicly available?
Rossco,
We are talking about catchment rainfall since this is vital for water security in Melbourne. The BoM data comes from the BoM weather stations at Maroondah and O’Shannessy Reservoirs, not stations closer to Melbourne. The data used was specifically chosen because the BoM stations were located the closest to 2 of Melbourne Water’s 4 main reservoirs.
I am aware that it is not possible to use urban rainfall data to show what is happening with catchment rainfall, that’s why I looked for the stations closest to the catchment areas.
Nichole,
I strongly endorse your call for Melbourne Water to put the information that they hold into the public domain.
“I also think that the data is out there. I wonder why, in a political climate where water is a key issue, this data isn’t publicly available? ”
The pure, simple and obvious reason would be money. It costs money to do all that. If you have ever looked after large data collections, and the publication of them, it’s not a trivial task. The BOM is a national body, and despite the copious amounts of data presented, which must have been quite an expensive task to set up for publication, there’s always something else that could be interesting that’s not there.
Nichole; there are many variables affecting long-term catchment yield besides rainfall. I noticed extensive urbanization at the fringe while flying over newer outer Melbourne suburbs recently and we can see all that using Google maps. Then there are all those extra tanks and ponds further out. Who knows how many now?
Given the complexity of the post ww2 MMBW developments I suggested finding old stream flow records (inflows) that must still exist for most of the primary storages. However all that which has been privatised tends to be unavailable or restricted somewhat by copyright.
There is also extensive studies regarding water yields in the forested areas beyond the greater Melbourne catchment.
http://search.informit.com.au/documentSummary;dn=652693757416653;res=IELENG
http://www.daff.gov.au/__data/assets/pdf_file/0007/97324/hydrology_catchment.pdf
http://www.csiro.au/files/files/pidd.pdf
Have fun
SJT,
I appreciate the costs involved. However, when I emailed the Sydney Catchment Authority requesting their data in excel format, it took a while, but they sent me the data. Why is the SCA able to do this when Melbourne Water can’t? In fact, Melbourne Water told me they didn’t have the data in excel format. This appears to be rubbish to me since there are plenty of excel graphs on their website.
The most cost-effective way for Melbourne Water to make this data publicly available is to put the excel files on their website, like the Bureau of Meteorology do with some of their data. Then, Melbourne Water don’t need someone to be looking for specifically requested information, they can direct people to their website.
Plus, Melbourne Water are imposing water restrictions on the public, with the constant message that water consumption needs to reduce because of less water in dams in the future. It is not unreasonable to demand that they show the public the long-term data that supports this view.
Gavin,
Thanks for the recommendation.
Nichole; the other most affected region identified on BoM S E Aus drought maps, is the area surounding the ACT. But of course you knew we had water problems too.
ACTEW may have similar stream flow studies available on request.
Good luck!
Jen and Nichole
The catchment forest issue is a diversion – if 2001-2008 is 2nd lowest rainfall sequence on record since the 1890s and 1996-2008 THE lowest on record since the 1890s – what would you expect but low dam inflows.
Indeed catchment vegetation may be an additional exacerbating factor – but surely lowest rainfalls on record is pretty basic.
That’s what your Yan Yean data says !
And SEACI have done the climate detective story as to why.
Luke: “The catchment forest issue is a diversion”
Its much more fun to be meandering through the clues in a well defined treasure hunt
Melbourne Water is owned by the Government, with a charter to make a profit. That was part of the privatisation that was never completed. SCA is a government agency, who’s charter is to provide a service to the people. 🙂
Nicole – may I suggest you get the raw Yan Yean data in Excel and check against BoM’s decile analysis here.
nice blog
Regards
Dimple
http://doctors-job.com