|
See the trough that wrecked NSW's wheat crop (animated image) Sail: Weather links: Stormwatch: La
Nina: Profiles: Surf: Sky: Polar: Ocean: Fire: Drought: Weatherfacts: Books: Products: |
Early wet season for Australia From
the threat of fires just two months ago, the main danger now is flood and crop
damage. November 24, 2000 New South Wales' grain farmers have hit an emotional low, with the realisation this week that most of their winter wheat crop has been destroyed by flood and persistent wet weather, just as they were about to embark on a bumper harvest. The remainder has all but sprouted in its seed pod, destined for animal feed at $80 per tonne, much less than the $280/ tonne it would have commanded as food-grade grain. Spring crops have been vandalised and some summer cotton crops lost. Uncounted cattle and sheep have perished. More than 27 per cent of the State is under water, with the Namoi river valley the worst affected. Astounding figures like 500mm of rain in the vicinity of Walgett this month, and a combined three-season economic loss of $1.1 billion dollars (half-a-billion this year alone), have underscored just how significant this early rainfall has become. And NSW is not the only region affected: Western Queensland and the border areas of Victoria have also dealt with a record wet November. Maryborough in central coastal Queensland, received 90mm in 15 minutes during a severe downpour around November 20. When you realise that the same amount of rain paralysed the UK during October, your begin to understand how extreme Australia's climate can be.
NSW has been dealt a savage economic blow as early summer rains destroy winter wheat harvest plans for the third year running. Flash floods Rain during November 19 and 20 in the Peel River catchment above Tamworth roared downhill overnight, cutting the country and western music capital of Australia in half before spilling brown murky waters onto the western flats. While certainly significant in their own right, the Dividing Range rains were more visually spectacular than damaging. Sure, towns like Gunnedah disappeared under water, but the damage to crops had already been done in the two weeks prior. Rivers threaten to burst their banks Four rivers most at risk of bursting their banks as of November 22 were the Namoi, Macquarie, Castlereagh, and Hunter. Except for the Hunter, which flows out to Sea at Newcastle, these rivers flow into the Barwon which forms the Darling upstream of Bourke. Others at risk of flooding were the Macintyre and Gwydir (these two flow into the Barwon), Bogan (forms the Darling at its confluence with the Barwon), Paroo (drains into clay pans west of Bourke and dies), Lachlan and Edward (both flow into the Murray upstream of Mildura) and Belbula rivers. Persistent trough? Persistent trough lines over central eastern Australia are not unusual. In fact, the typical La Nina 'signature' includes a trough right through the guts of the country, bringing flood to parts, and astounding green growth to others. This region of enhanced rainfall, in association with a strong monsoon in the tropics, has been an almost permanent fixture for the last two summers, as La Nina ran her course with a strength not seen for decades. In fact, the above average rainfall last summer was much more widespread than the classic pattern. Farmers in the Namoi River valley have lost their previous two winter wheat crops to La Nina's early summer rains. This year was supposed to be different. La Nina had all but disappeared when farmers planted their winters seed, and all models except for COLA, predicted neutral conditions at the end of 2000. Only the COLA model indicated yet another cool phase in the Pacific equatorial cycle. But the Australian spring went from bone dry to unusually wet during the month of October, culminating in the wettest Novembers on record - wetter than 1961 and 1984. The Southern Oscillation Index, a key indicator of Pacific climate, stands at 16 in the positive range and is rising, indicating - at first glance - plenty more wet weather this summer. Grant Beard, climate forecaster with the Australian Bureau of Meteorology, notes that the trough which flooded the NSW Outback was not unusual. If anything was unusual, he says, blame the high pressure cell east of the NSW coast. Normally a high will ridge up the coastline, driving south easterly winds onto northern NSW and south-eastern Queensland. Instead, this high directed easterly and north-easterly winds well inland for more than a week. The warm, moist, sub-tropical oceanic air penetrated west of the dividing range and flowed into the trough from underneath, rising as cloud and returning to earth as rain, rain, and more rain. "The trough wasn't as strong as some," he says, " but the moisture content was critical." Is Australia looking at another La Nina summer? It is too early to tell, says Beard. The way trough lines are stalling over central-eastern Australia, the fact that the SOI is quite high and rising (for the last 30 days the SOI has been at 16 plus), are certainly characteristics of La Nina. But at this stage the equatorial Pacific is responding slowly. Sea surface temperatures along the east and central equator are slightly cooler than normal. "But it is very weak at this point," says Beard. "It is certainly no where near as strong as last summer, which was one of the wettest since 1900." Why didn't Australia's three-month forecast predict this extra-ordinary November? According to Beard, climate prediction models 'tell us how the climate dice are loaded', he says. "But they don't tell us what luck they will bring." Where will the water go? It takes two to three months for water falling above Tamworth to reach the mouth of the Murray River on the South Australian coast. Water in the outback moves sluggishly, a great slow moving pulse of muddy brown water which gives life to the water courses down which it travels. According to Australian Bureau of Meteorology hydrologist Hugh Bruist, flood peaks are calculated from river gauges and landholder information - a wide network of information gleaned from many sources. Past floods give forecasters a reference point, with data plotted on graphs. Volumes are calculated and peaks predicted. The condition of the flood plain is taken into consideration, as well the timing of the major flood waters from the various rivers as they enter the Barwon-Darling River. Of course, things get difficult when peak floods from different river systems converge at the same time in parent tributaries. Fortunately for residents along the banks of the Barwon and Darling rivers, peaks during this flood are moving through the outback separately, resulting in moderate inundation. However, the wide brown land of the outback will remain the wide brown sea for some time. The flood peak will arrive at Walgett in early December, Bourke on December 20 and Louth on December 27. Wilcania residents can expect a minor flood peak sometime in mid January. From here the water is only half-way to the coast. It will be late summer before this 'fresh' hits the salt of Encounter Bay, south Australia.
Record wet November 20 (Reuters): New South Wales has had its wettest November on record, the Bureau of Meteorology has said. The worst-hit districts are the North West Slopes and Plains and the Upper Western, recording between 200mm and 300mm so far in November. Weather experts say the wettest place is Mount Seaview on the Mid North Coast which has recorded 344mm this month. However, Murrurundi in the Upper Hunter has broken its previous record of 200mm, with 326mm so far this month, of which 300mm has fallen in the past week. Some parts of the South West Slopes and the extreme far north-west of NSW are the only areas of the state to have escaped the downpour, still yet to achieve their average rainfall for November. See the trough
that wreaked havoc More great reading: Australian three-month climate outlook. Sea surface temperature anomolies - world-wide:
© weather-wise.com 2000 |