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Big dry for a little island
Longest drought in living memory confounds forecasters, July, 2000 Geoff Parsons has a family connection on his Derwent Valley property going back to the 1860s. Never before has he, or his 89 year old father, known it to be so dry. What interests those studying long-term climate cycles, is the fact that the drought affecting Tasmania’s central midlands and upper Derwent Valley appears to be unrelated to changes in Pacific ocean temperatures - unlike the rest of Australia. "Some of us believe it has more to do with the Southern Ocean than previously thought," notes Mike Pook, of the Antarctic Co-operative Research Centre. This drought gone on through the end of one El Nino and through the latest La Nina so obviously there is something else involved." However, Pook is reluctant to comment further because records for this region are too lean to make assumptions on climate cycles. But 120 years of rain charts do show that drought has come before, and no doubt it will come again. The 1890s were especially bad, so too were the years including the first and second world . The 1940-45 drought was particularly wicked, but those that can remember it in detail are thin on the ground. "You’re dealing with people who effectively can’t remember that drought very well," reminds Pook. "It was nearly 60 years ago and there are not many people around who had a clear recollection of those times." "A number of people would say that essentially the life of a farm manager is in the order of 30 years. Therefore if something doesn’t occur within that time, then it is hard to make comparisons with earlier events." Worst in living memory Geoff Parsons’ father is one who does remember clearly, the droughts of old. "My father, Doug, is 89 going on 90 and he says this current dry is by far the worst he’s seen or known about," says Parsons. "In the past, when it got dry it might be that way for a year, but they had a good season each side." Average rainfall is now 290mm (11½ inches), or half of normal, and where 10,000 sheep and 150 beef cattle used to graze on green slopes, thin grass has meant stock numbers are down to 6500 sheep and 80 cattle. Those stock that remain are in low store condition when they should be good. Micro-climates Tasmania is home to a number of micro-climates, from the cold and wet west coast, which is affected by frontal cloud bands from the Southern Ocean, to the dry north-east coast, which relies on rainfall from ex-tropical depressions and lows forming off the east coast of Australia. In winter, gales traveling through the Bass Strait and intensifying to the east, bring soaking rains to the top end of Tasmania, and in the past provided the now-dry valleys of the upper Derwent with enough moisture to stay in business. But something has changed since 1997 and as you travel west from Hobart towards the central highlands, pockets of country tucked away in undulating valleys are getting drier, and drier. The town of Hamilton lies about 10km as the crow flies from the Parsons’ property. Normally it receives about 460mm (18 inches) of rain. In the last year it got 255mm (10 inches). Mt Field and surrounding mountains are visible to the west and their tops receive something like 1500mm (60 inches) of rain a year. Strathgordon, on the western slopes of the central highlands, gets plenty of wet weather, with 20 and 40mm (3/4 to 1½ inches) falling each time a frontal system crosses the coast. "We’re 100km to the east of Strathgordon and we don’t get anything," says a frustrated Parsons. Last year the Parsons improved one paddock by spreading 300kg of potash and super phosphate on each hectare of soil but without adequate rains, the grass grew just four inches and was as thin as old man’s hair. "We’re just not getting the winter rains like we used to," he laments. "We’ve had more summer rains for last four years. They’re good, but a fortnight later the moisture dries out from the heat. Winter rains soak into the ground and the moisture comes out in spring, giving you good spring growth." To help ease the burden, farmers in the north of Tasmania have donated 1000 big round bales of hay and 2500 square bales. The trick now is to distribute them evenly. Parsons notes that in past years, they’ve ‘cut hay here every year we could shut up a paddock and cut it’. In the last five years the family farm has seen only one good hay crop. "Its our surface water which we want to get back," says Parsons. "People are carting water. We have one water hole, quite a big one, and we will have to make a decision soon whether to pump out of that one to another three km away and 200 feet higher in order to water another portion of the property." Persistent high pressure According to Tasmanian Bureau of Meteorology forecaster Malcolm Riley, no one knows for sure why portions of Tasmania are facing their worst drought in living memory, but air pressure has something to do with it. Riley says that for the last three years the average atmospheric pressure has been higher than normal over northern and eastern Tasmania, eastern Bass Strait and south eastern Victoria. "The lows haven’t been as intense and the highs are stronger and last longer," says Riley. "There’s been good rain in the west of the State, but something has kept the easterly rain-bearing systems away from our coast." Flinders Island, off the north coast of Tasmania in Bass Strait, has borne the worst of the drought over the last 40 months and across the strait, south-eastern Victoria has also faced severe water shortages. Elsewhere in Australia, farmers have been cursing a prolonged wet weather spell, not seen for 25 years. Riley does note that El Nino seasons tend to keep east coast lows away from Tasmania and that might help explain the drought from 1997 through late 1998. It does not explain the drought continuing through the recent La Nina event. Anyway, farmers on the Apple Isle have been recording sliding rainfall figures for the last 15 years. Parsons tells it like this: 1944-45 brought the biggest drought to that time, but it wasn’t long term; ‘In and out’ as his father told it. The 1950s were wet, the 1960s dry, coinciding with massive bush fires that threatened Hobart in 1967-68. The 1970s were wet, the 1980s were mixed and from 1990 it just got drier and drier. "Usually in September we can count on new growth, but now we might have to start changing our tactics. And we don’t know what those tactics will be," laments Parsons. Can an unusual climate wobble in the Southern Ocean be responsible for Tasmania’s current drought? Blocking highs in the southern Tasman contribute to good rainfall over the Apple Isle. © weather-wise.com 2000 |
Did you know? Tasmania can count on rain
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