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| Land clearing may have had the unintended effect of lowering rainfall in South West WA. (Getty Images: Australian Scenics) |
After 200 years of changing the landscape of the
world's most distinctive continent we are only just beginning to
understand how European settlers and their successors have vitally
affected its ecology, its diversity and its climate.
And while those effects pervade much of our island continent, they are singularly visible in Western Australia's South West.Recording social history for RN's Hindsight program in the 1980s, an interview with an observant old forester, Jack Thompson, offered me an early lesson.
Jack worked for most of his life in the jarrah and karri forests of the South West, initially as a tree feller and ultimately as a conservationist.
Audio: Listen to Bill Bunbury's report (Science Show)
One vivid recollection was his daily journey to work from the forest camp.
"I remember once, we were camped on the Balingup Brook and we couldn't find a place to cross this brook," he told me. "It was in flood, about 30 feet across and waist deep.
"Every man cut his own crib [lunch] and you hung it on the back of your belt. So to get across we'd lift the crib up and just wade through this icy water up to your waist. But after you'd walked for half a mile, you'd walked yourself warm again. You took that all in your stride."
It's a story that stayed with me. Not so much that the redoubtable Jack took it all in his stride, but because the Balingup Brook no longer floods the way it did in his day.
Rainfall has declined significantly in this part of Australia. Anecdotes are sometimes evocative reminders of change.
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| The climate of South West WA has changed appreciably in the last century. (Getty Images: Dazman) |
More recently, writing a book for the WA Department of Water, Till the Stream Runs Dry, I talked to those now responsible for measuring the considerable decline in rainfall: men like hydrographer Bernie Hawkins, whose career began in the 1960s.
"The winters then were massively wetter," he said. "We were in waterproofs, wellington boots and sou'westers most of the winter."
But even 10 years later, things had changed: "We were quite aware that there had been a change in rainfall. The winters weren't the same. We kept on saying it all the time as the years went by."
Large areas of the South West had been cleared, most heavily in the last century. Forests fell to make way for wheat, which had a direct effect on rainfall. The old settler saying "rain follows the axe" could easily be re-stated as "rain heads for the woods".
It has recently been shown that where rain meets woodland, trees attract rainfall. As rainclouds cross a landscape and encounter higher ground and/or wooded areas they are much more likely to shed their contents. By contrast, where rain sweeps across a largely un-treed landscape, not much reaches the ground.
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| Map of rabbit proof fence near Lake King, WA |
Woodland, farmland and scarce water sources are all vitally interconnected in ways we are only beginning to understand. But uncertainty and unpredictability also complicate our understanding of climate change. We are still learning surprising lessons.
For instance, frost is now more frequent on winter nights, especially in the far south of WA, and affects both farm and forest. But there is a logical explanation. Cloudless, non-rain-bearing skies are colder.
CO2 has the potential to encourage plant growth and perhaps increase forest cover, minimising the risk of further drying. But it doesn't. CO2 is best absorbed by the lighter hued deciduous trees that dominate much of the northern hemisphere. Much of our antipodean vegetation is too dark to permit effective CO2 absorption.
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| Despite the end of the mining boom, Perth and its suburbs continue to grow. (Getty Images: David Messent) |
Changing silviculture practices may well assist. Our forest clearing has often resulted in thirsty, younger, denser forest, which might benefit from thinning to allow more groundwater to sink into the water table.
Regardless of where we live, the South West has lessons it can share with the rest of us.
As environmental scientist Joe Fontaine points out, this corner of the continent, with its Mediterranean climate, offers "many sometimes cautionary tales to the rest of the world".
"Areas throughout the world with this type of climate are warming and drying. So south-west Australia is a case of a 'canary in a coalmine' for understanding what climate change impacts may mean in in the future."
It's not the only "canary" in the world, but it's ours.
Links
- How Climate Change Will Shape Environmental Law
- Climate trends in Western Australia | Department of Agriculture and Food
- About climate change in WA - Department of Environment Regulation
- WA Speaks: Climate change to hit state hard, West Australians concerned about global warming
- Australian climate influences - Climate Change in Australia
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