500 years of drought and flood: trees and corals reveal Australia’s climate history
By Paul Homewood
I may have covered this at the time in 2015, but it’s worth repeating:
Australia is the land of drought and flooding rains, and in a recent paper we’ve shown that’s been the case for more than 500 years. As part of our Australia and New Zealand Drought Atlas we’ve published the most detailed record of drought and wet periods (or “pluvials”) since 1500.
The data reveal that despite the severity of the Millennium Drought (2001 to 2008), the five worst single years of drought happened before 1900. But 2011 was the wettest year in our 513-year record.
The dominant theme of Australia’s drought history is variability. We may get one year of extremely wet conditions (for example in 2011) or we might get six years of extremely dry conditions (such as 2003-2009).
North Queensland may be flooded out while Victoria suffers with drought. Or in extreme circumstances, the entire eastern half of Australia might be bone dry.
The existing drought records are relatively short and geographically patchy. Measurements from weather stations rarely extend beyond the early 1900s and informal historical records from diaries and ships logs — some of which go back to the first days of European settlement in Australia — are relatively uncommon and limited to a few sites. This has limited our understanding of drought variability to what has been directly observed over the past 120 years.
To extend the drought record beyond 1900, we used 177 tree ring and coral records from Australia, New Zealand, and Indonesia to reconstruct summer (spanning December to February) drought conditions in New Zealand and most of Australia.
Trees and corals are sensitive to their environments. For example, trees grow less in dry years and more in wet years. We carefully examined, dated, and measured each growth ring in thousands of trees and then compared the patterns of growth to an index of drought variability, the Palmer Drought Severity Index.
Over the past five centuries we found extreme droughts similar to the recent Millennium Drought, but we also discovered wet periods that lasted decades.
We found short droughts of brutal intensity that blanketed all of eastern Australia, while other droughts of similar intensity were confined to small pockets across the continent.
The atlas also provides new geographical context for early historical droughts. For example, diaries from early settlers near Sydney documented a crippling drought in 1791-92. Our data demonstrate that this was one of the worst drought years in the past 500 years with extraordinarily dry conditions that stretched from Cape York to eastern Tasmania. The early colony was fortunate to survive.
An obvious question is how do our modern droughts and floods stack up against earlier events? Of the five most extreme single years of drought in the past 500 years (when averaged across all of eastern Australia), not one occurred after 1900.
In contrast, two of the five wettest years in our data took place after 1950 (2011 was the wettest year in the 513-year record). The 1700s were particularly dry with three of the five worst drought years, but also notably had the most prolonged wet period (1730-60).
In eastern Australia, wet and dry conditions cycle back and forth over several decades, driven by the oceans around us.
When we compared the data to a recently developed index of changing atmospheric pressure called the Interdecadal Pacific Oscillation (IPO), we found remarkable consistency between the two. The IPO tells us when we have unexpectedly warmer or cooler sea surface temps and air pressures. The IPO also interacts with El Nino and La Nina to make them stronger or weaker.
When the IPO was positive, eastern Australia experienced drought conditions for several decades; when it was negative, eastern Australia experienced pervasive wet conditions. From 1999-2012 we were in a negative phase of the IPO; now it appears we have just entered a strongly positive phase.
You may have noticed that the Millennium Drought happened in a negative IPO phase. Our data show that there is a strong relationship between the phases of the IPO and drought – until around 1976. After that the relationship gets weaker. Why is a question for further research, but one possibility is human-caused climate change.
This new data will help us understand what drives these swings between drought and floods, and help us predict what might happen in the future.
Their conclusions that droughts were much more extreme prior to 1900, and that the climate appears to be wetter are both significant.
The paper contains this reconstruction, based on the IPO index and tree ring data – negative values indicate drier conditions:
http://iopscience.iop.org/article/10.1088/1748-9326/10/12/124002/pdf
The severe droughts of the past stand out, notably the early 20thC ones and the 18thC, such as 1791-92:
It’s food for thought! One wonders what might have happened if that early colony had not survived?
Comments are closed.
NOT A LOT OF PEOPLE KNOW THAT 
‘For example, trees grow less in dry years and more in wet years.’
And they grow less in cold years than warm years.
Amazing that they are able to tease out the moisture part of tree ring growth from the temperature part.
In other words, disregard the study. It’s bogus.
Many of these reports seriously puzzle me. Why say things like
“North Queensland may be flooded out while Victoria suffers with drought.”
Well so what? They are nearly 2,000 miles and 30° latitude apart so surely nobody would expect their climates to be similar. Why add words pointing out the bleeding obvious? Word count padding?
Ignorance?
I think you are a bit unfair. Mann’s unswerving attachment to dendrochronology and hookey hockey showing only temperature signal (apart from a bit of cherry picking) was egregious.
These guys really show hot and or dry vs milder and or wetter and you really dont need to tease out individual components to differentiate nice and nasty
I have no duty to be fair when I am being lied to.
Alternatively disregard temperature reconstructions such as Mikey Mann’s hockey stick that rely heavily on tree rings.
An old Aussie farmer told me that there was very good reason that ancient ‘Australian’ society never developed from nomadic to agrarian: the climate. He reckoned the last couple of hundred years of occasional good harvests were the exception.
.. why go to Australia? We have Coral (Reefs?) here in the UK: Recent tv prog showed Coral in the N Sea off Norfolk / E Anglia area, Off NW Scotland, and deep water Coral up there too. so what do they tell us about this area ?
why go to Australia? Its warmer there. We cant wait for mythical global warming to make the UK a pleasant climate. Burn some more coal you buggers and warm this country up – wishful thinking, if only it would work!
It’s got poisonous snakes (100 varieties) including sea snakess, poisonous spiders two of which can kill you and a fair number of deadly fish. Even mammals with venom.
Far too dangerous, the only good thing about a cold climate poisonous critters don’t like it either.
Don’t forget, Michael Mann used tree rings as proxies for TEMPERATURE.
“High-resolution proxies,” the contemporary press reported.
The science is settled.
Well, he did, until the tree rings showed a declining temperature so he stuck the instrumental record on at the end.
“Trees and corals are sensitive to their environments.”
But not modern politicians. Then a revolution comes as a surprise.
Living on Vancouver island I have taken many trees down and looked at tree rings many a time. You never see the same ring twice,even when cutting trees a few feet apart. Way too many variables water run off,sunshine,injury from other falling trees. Tree rings tell you what ever you want them to. That whole science is absurd. When we know what the climate has been for sixty years but can’t tell from two trees a hundred feet apart one would have to say the whole tree ring thing is garbage.
There has to be similarities in patterns of tree rings. Dendrochronology dates wooden artifacts by comparing ring patterns with patterns in wood of a known age. The dates can be checked with radiocarbon dating and shown to be accurate. The difficulty is knowing whether is good growing year is the result of warmth, and if so is it just warmth during a particular season, or the right amount of precipitation at the right time of the year. The right amount of precipitation will be different for different species, and some species might be temperature sensitive while others are moisture sensitive. Presumably scientists can work out the relative importance of different variable for different species by comparing modern tree rings with weather data then be able to reconstruct past climate with a good level of accuracy. Using a lot of different trees and taking an average should minimise errors caused by the factors you mentioned.
The science can be absurd, or as you said made to show what people want it to show. There was a version of the hockey stick that used tree rings from a larch in Yamal, Siberia that showed increased rates of growth in the last 50 or 60 years because nearby trees had been felled so the larch started getting more light. The algorithm used to produce a hockey stick shape attached massive weight to this single data set so that Yamal became over 50% of global land area. Good, non agenda driven scientists should be able to avoid these errors/deliberate deceptions.
This reminds me of the Bacon-messages-in-Shakespeare problem. Cryptographers seem to have laid it to rest, even assuming Bacon could find the time to insert text subject to so many varying interpretations. Inkblots will be inkblots, no?
The comment about “Measurements from weather stations rarely extend BEFORE the early 1900s are relatively uncommon and limited to a few sites” are misleading. Sir Charles Todd was in charge of building telegraph lines between Adelaide and Melbourne, Darwin and to the Western Australian border. He was a prominent believer in weather (FRS) and each telegraph station had to report daily about local temperatures and weather. He also supervised the station at West Terrace (Adelaide) where he had at least 6 differing units** as well as an astronomy.
There was a mass of records, all of which the latter Commonwealth Bureau of Meteorology ignore, and still considers that weather records in Australia only began with theirs in 1910. Their current performance would not meet Sir Charles approval.
**He instituted the longest running comparison between the Glaisher and Stevenson instruments (36 years).
Waitaminnit… Whutabout the 1961 Soviet storyboard? Warmunism? Sharknados? It all seemed sooo real!
https://cdnsciencepub.com/doi/10.1139/cjfr-2020-0182
Test. Here is a paper on the history of dendro chronology .
Dendroclimatic investigations and cross-dating in the 1700s: the tree-ring investigations of Johan Leche (1704–1764) in southwestern Finland
I prefer the use of tree rings in timber building investigations to prove similar dates in a small area. or repairs to a large structure .
And
. Each piece of woodland has it’s own history
of moisture and sunlight and natural forest fire so the general climate of a larger geographical area at any one time in the Past is very difficult to find. Dryness may be caused by rivers moving their channels, for instance.E
“Dryness may be caused by rivers moving their channels, for instance”
My parents former house on the edge of the Romney Marsh in Kent, was built on the former course of the River Rother. Apparently many hundreds of years ago a severe storm changed its course out to sea by a long way indeed. It seems strange now to think that such dramatic changes could occur almost literally overnight.
When they moved in we actually landscaped the garden by digging out the still evident old river banks. The centre of the old course was almost pure sand and would warm up in spring almost as fast as it nearly froze in winter. Very strange indeed considering the surrounding area was heavy clay overlaying chalk.
They’re still pushing this one…
In the future, wet-hot extremes will become more likely because the atmosphere’s capacity to hold moisture increases by 6% to 7% for every 1 degree Celsius rise in temperature. As Earth gets hotter, the warmer atmosphere will hold more water vapor, meaning more water will be available to fall as precipitation.
https://phys.org/news/2023-09-communities-encounter-heavy-rainfall-excessive.html
Implies more evaporation, and that ‘getting hotter’ is a constant.
The Clausius- Clayperon relation is probably the most deliberately misquoted formula of all climate claptrap. Though above is correctly quoted as in “capacity to hold water” so many rag journalists (i.e. the Guardian/BBC) deliberately omits the word “capacity” and simply claim that the amount of atmospheric water vapour increases 7% for every degree of warming….it doesn’t.
Yes, they seem to think that the atmosphere is fully saturated all the time.
I stumble on the logic that because the atmosphere can, allegedly, hold more water, it will rain more. Rain is the opposite of holding. So, apparently, it will hold more til it’s time to rain, then it will go back to holding what it used to, the difference then being more rain. Or something.