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ENVIRONMENT

Rain can't drown climate truth

  • 22 November 2010

Two creeks that were bone-dry for years are flowing again across my hilly bush block. The dams on properties upstream have filled to overflowing, and natural springs in the hillsides have opened again. After so much recent rain, the land feels like a big wet sponge.

Down the hill in the Burra Valley, fat merinos graze in lush pastures. I haven't seen the valley look so green since the 1970s. Canberra's nearby city water dams, which were 30 per cent full three years ago, are now 90 per cent full. With ample water has come a new sense of peace and security across our region.

I wish I could say this is an end to drought and water scarcity in the Murray-Darling Basin, where I live. But the science tells otherwise.

Southern Australia is an area of high natural rainfall variability, irrespective of climate change. These variations are caused by the El Nino/La Nina southern ocean oscillation, and the Indian Ocean dipole. Similar temperate-zone regions of high rainfall variability over irregular periods of a few years are in southern Africa, southwest USA, the Mediterranean rim, and northern China.

All these areas require water storage systems (dams, wells, bores, irrigation systems) for safe agriculture that can help protect farmers from the variability.

As a result of the past two good 'La Nina' years of better rainfall, the Murray-Darling system has started flowing again all the way to the Coorong Lakes at its mouth. Wetlands are refilling and the basin's subsurface reservoirs are being replenished.

But climate change has not gone away. Rising greenhouse gas concentrations continue to heat the atmosphere, causing increased weather extremes, and changes to climate zones: the tropical zone expands, the polar zone shrinks, and the temperate zone in between moves polewards.

We see this in Australia: less rain is falling in southwest Australia and the southern parts of the Murray-Darling basin, less snow is falling in the highlands, but there is more tropical cyclone-influenced rain in the far north of the basin and even in the Lake Eyre catchment in southwest Queensland.

It takes expert statistical analysis to disentangle southern Australia's highly variable rainfall oscillation from the secular climate change trend of increased heat energy leading to changed weather patterns. But the existence of such a

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