Jennifer Marohasy

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Bunny fence prompts land use study in Western Australia

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There’s an interesting article in The New York Times entitled ‘At Australia’s Bunny Fence, Variable Cloudiness Prompts Climate Study.’

“A fence built to prevent rabbits from entering the Australian outback has unintentionally allowed scientists to study the effects of land use on regional climates.

The rabbit-proof fence in Western Australia was completed in 1907 and stretches about 2,000 miles. It acts as a boundary separating native vegetation from farmland. Within the fence area, scientists have observed a strange phenomenon: above the native vegetation, the sky is rich in rain-producing clouds. But the sky on the farmland side is clear.

Researchers led by Tom Lyons of Murdoch University in Australia and Udaysankar S. Nair of the University of Alabama in Huntsville have come up with three possible explanations for this difference in cloudiness.

One theory is that the dark native vegetation absorbs and releases more heat into the atmosphere than the light-colored crops. These native plants release heat that combines with water vapor from the lower atmosphere, resulting in cloud formation.

Another hypothesis is that the warmer air on the native scrubland rises, creating a vacuum in the lower atmosphere that is then filled by cooler air from cropland across the fence. As a result, clouds form on the scrubland side.

A third idea is that a high concentration of aerosols — particles suspended in the atmosphere — on the agricultural side results in small water droplets and a decrease in the probability of rainfall. On the native landscape, the concentration of aerosols is lower, translating into larger droplets and more rainfall.

Within the last few decades, about 32 million acres of native vegetation have been converted to croplands west of the bunny fence. On the agricultural side of the fence, rainfall has been reduced by 20 percent since the 1970s.”

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Comments

  1. Luke says

    Research undertaken by the Indian Ocean Climate Initiative (IOCI) http://www.ioci.org.au/ and reported by CSIRO http://www.csiro.au/news/ps2y1.html attributes the decline in SW WA rainfall to a combination of anthropogenic and natural changes in climate.

    Nevertheless the rabbit fence “effect” as we have previously discussed here on blog last week is pretty interesting.

    Do the clouds translate into rainfall though?

  2. Paul Biggs says

    The land-atmosphere interaction is not restricted to Australia – land use change may be an underestimated anthropogenic factor.

    I guess more clouds gives more chance of rainfall.

    I note that the fence didn’t succeed in keeping out Bunnies, but it did keep out Kangeroos and Emus.

  3. John says

    I would like to know precisely where this occurs and what time of year so that ISCCP cloud cover data can be checked. That ISCCP data is known to have some problems especially wen reaching the extremes of the “view” from a satellite.

    I question the claim that warmer air exists over the native bushland than over the farm land because the farmland will be devoid of vegetation from around December until May if it is wheat country. If it’s sheep country then the grass will be short and bleached during summer. That bare or almost earth will absorb heat but transfer of heat within the soil is poor and the surface will remain quite warm. (If the researchers aren’t aware of the basic farming practices with each season you’d have to wonder if they were city boys who never visited the area!)

    Based on the above it seems likely that the absence of cloud over the farmland is due to warm moist air off the ocean meeting the warm dry air over the land. That’s enough to make the air rise and the cloud disappear, then as the air-stream moves east the air over the land is cooler and cloud re-forms.

  4. Boxer says

    It’s a striking sight when you fly over it. I flew up to Kununnura (town in the far north of the state) a few years ago. I commented on it to the guy I had flown up to visit, and he said it was a common feature. My recollection is that it went from clear sky to about 50% cloud virtually right over the boundary of the last farm.

    The native bush would transpire more water vapour than the farmland during the dry summer period, but I saw it in spring (I think, maybe winter), so the crops were green.

  6. Allan Ames says

    Assuming that clouds “cool” this certainly makes a strong case for AGW. Unfortunately, I think it would be easier to give up fossil fuels than farming.

  7. rog says

    Evidence that areas of irrigated agriculture lowers temperatures, possibly through evapo and/or transpiration. You would have to monitor humidity and prevailing winds for a clearer picture.

  11. Luke says

    There have been studies relating aspects of Sydney storms with land clearing in the basin.

    http://www.pr.mq.edu.au/macnews/showitem.asp?ItemID=431

    http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2FJAM2337.1

    http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VF0-4K9C5FS-2&_user=10&_coverDate=11%2F30%2F2006&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=7e16213adeaf35a470b99de6275253bc

  12. John says

    rog made a good comment “…You would have to monitor humidity and prevailing winds for a clearer picture.”

    It makes me wonder why no weather balloons have been launched on both sides of the fence under calm conditions, preferably on the same day so that temperatures were comparable. They’d collect the necessary data and help clarify what is really happening.

  14. Davey Gam Esq. says

    The New York Times starts off on the wrong foot. The RPF No. 1 (north-south) was not built to prevent rabbits entering the outback. It was the other way round, to prevent rabbits from the outback (east) entering the inback (west). As Paul says, it, and RPF No. 2 (east-west) both failed with regard to bunnies.