Jennifer Marohasy

a forum for the discussion of issues concerning the natural environment

Archives for August 2006

Where has all the Marsh Water Gone?

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It has been suggested that before irrigation runoff into the Macquarie Marshes was 460,000 megalitres and that this has been reduced to 395,000ml by irrigation.

But Ian Mott has argued that pre-settlement runoff into the marshes would have been much less than 460,000ml and most likely less than 395,000ml because much of the upper catchment was once forested. Because it has since been cleared for pasture, runoff would have substantially increased.

Yet the opposite appears to be the case.

In an earlier thread Chris Hogendyk expained that: “Inflows to Burrendong (on the catchment of the Macquarie) for the 68 months from December 2000 to July 2006 was approximately 1700 GL which is the same as the driest similar period on record that occurred from December 1934 to July 1940. The next driest period was December 1903 to July 1909 that received approximately 1950 GL.

“The first data set are actual observations whilst the latter two are modelled. Out of interest, for every 10 megalitres that is captured by the dam, 4 megalitres come into the system as down stream tributaries.”

Interestingly rainfall history as plotted by Warwick Hughes suggests that it was drier during the late 1930s.

trangie05blog.GIF

bathmudg05 blog.GIF

This is Warwicks comment on the charts: “These show you some rainfall history for the region from the Bureau of Metereology high quality rain dataset and you can see the obvious cycles in all charts.

“Trangie data is the closest HQ station to the Macquarie Marshes and it shows that in the recent past conditions were similar to dry times times in the 1990’s and 1980’s, if you go back to the 1960’s rainfall was obviously less and even lower in the late 1930’s thru 40’s and earlier again WWI years into the 1920’s look the driest of all.

“The other graphic, also of HQ data, from Mudgee and Bathurst, could be a fair proxy for long term trends higher in the catchment.”

So it has been dry, but not that dry, and with fewer trees, why have inflows been so low lately?

Farmed Fish are our Future: Conference in Adelaide

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Aquaculture is the fastest growing food producing sector in the world according to those promoting a fish farmer’s conference in Adelaide this week.

Farm Online have reported that there are 1,000 delegates at the conference and aquaculture is being talked-up with conference organising committee chair, Bruce Zippel, saying, “Many Australian primary producers are looking to supplement their incomes or moving into a more rewarding vocation .. and fish farming is seen as very attractive”.

Aquaculture apparenty provides about 27 percent of total world seafood supply and some experts predict that within 25 years half of the fish we eat will be farmed.

Sea Levels Falling in the Arctic?

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According to an article entitled ‘Arctic dips as global waters rise’ published at BBC News, sea levels in the Arctic have been falling by a little over 2mm a year. It goes on to explain that while it is well known that the world’s oceans do not share a uniform height, the scientists are nevertheless puzzled by their findings. And so am I.

Read the full article here.

Shifting the Environmental Impact of Fishing Somewhere Else

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“Australia has the third largest fishery zone of any nation. It also has the most over-managed, heavily restricted and least productive fishery sector in the world,” according to marine biologist Dr Walter Starck.

“The total Australian wild caught fishery harvest is less than half that of New Zealand and less than a tenth that of Thailand which has a fisheries zone only 5 percent the size of Australia’s.

“Seventy percent of the seafood we consume is imported, all of it from regions far more heavily fished than our own.”

Dr Walter Starck will be in Brisbane on 23rd September to speak at the inaugural Australian Environment Foundation conference.

Show your support for the new more evidence-based approach to environmental issue advocated by the AEF and register for the conference: http://www.aefweb.info/display/conference2006.html .

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I’m a director of the AEF.

Rats Destroyed the Forests on Easter Island: Terry Hunt

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Easter Island has been described by Jared Diamond as the “clearest example of a society that destroyed itself by overexploiting its own resources”.

Prof Diamond has told and retold the story and drawn a parallel between the ecological disaster he says befell Easter Island and our likely fate because we are cutting down too many trees and consuming too much energy.

In the September-October issue of American Scientist Online Terry Hunt details findings from his work on Easter Island.

It is an interesting read in which Hunt concludes that rats introduced by the Polynesians negatively impacted on recruitment in Jubaea palms resulting in forest decline. In contrast, Jared Diamond says the Polynesians simply cut down all the trees.

Furthermore Hunt suggests that the downfall of the original Polynesian civilization resulted not from internal strife associated with ecological disaster following destruction of the forest, but rather from contact with Europeans.

I read a lot of James Michener books when I was a bit younger. Civilizations destroyed by new arrivals is a consistent theme in Michener’s stories.

Drought & Temperature: An Update for Australia from David

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Jen,

I’ve noticed your recent thread on the long-term hydrological drought affecting eastern Australia. I’ve whipped off a few charts for you which put this into an historical context based on rainfall data going back to 1900 (some limited earlier data is available).

In terms of eastern Australia, the current meteorological drought started in early 2002 with the emergence of an El Nino event and continues to the present. The first figure below shows essentially drought “deciles” for this period.

BOM jan02-06 rainfall deciles blog.JPG

As you can see a significant part of SE Queensland has experience its driest 55 month period on record. The data are not spatially dense enough to resolve structures at the catchments scales (though Warwick’s graphs suggest ~5 yearly rainfalls which are lowest on record).

Note that the analysis only shows those areas which are experiencing severe or serious meteorological drought (almost all of eastern Australia has experienced below average rainfall through this period).

Rainfall is only part of the drought story (drought is a function of both water supply and water demand), but it does support the general conclusion that it has been abnormally dry and probably the driest period in “of order” 100 years.

This is just one of three protracted drought periods which Australia is experiencing. Probably the most important from a water management perspective is that which started in early 1997/late 1996 in southern Australia. This is shown in the second figure.

BOM jan97-06 rainfall deciles blog.JPG

This has seen the Perth, Canberra and Melbourne catchments all experience their lowest (or nearly so) rainfall on record. The third protracted drought event is that which commenced in SW Western Australia in the 1970s and which has been linked to a combination of greenhouse gas increases, ozone depletion and natural variability by the Indian Ocean Climate Initiative (see http://www.ioci.org.au/).

An aspect which is not covered in these analyses is the high temperatures. The third figures shows the mean temperature deciles for the period starting in 2002.

BOM temp deciles jan02-jul06 blog.JPG

This analysis is based on the post 1950 period only (though temperatures before this time were generally considerably cooler) and uses only the high quality national temperature network discussed at http://www.bom.gov.au/climate/change/reference.shtml .

These stations have minimal or no urban heat island effects. There are a number of papers published on the increasingly warm temperatures which we now experience with droughts (as a result of global warming interacting with climate variability). As you can see almost everywhere has been warmer than average and most of Queensland has experienced its warmest 55 month period on record.

Regards,

David