A deluge of good news

COOL wet weather and La Nina's retreat has farmers rejoicing.

THE release this week of Ross Garnaut's final climate change report coincided with confirmation from the Bureau of Meteorology that Australia had just experienced its coolest autumn since the 1950s.

In addition, the first solid rains for two years have all but broken the drought that has crippled the West Australian grain industry, easing concerns that the rainfall patterns of the past two years have become a permanent climate change fixture.

And the La Nina weather pattern that produced the summer of natural disasters, such as widespread flooding across three states and Cyclone Yasi in north Queensland, leading to much conjecture about whether this was climate change at work, has eased to neutral.

The welcome news on each front in no way undermines the conviction in Garnaut's climate change message. But each highlights that weather and climate are two different things that are too often easily confused.

According to BOM nationwide, this autumn beat the previous record for low average temperatures set in 1960 (-0.95C), with temperatures below the 1961-90 average.

Newly digitised data available to the bureau suggests 1917 was cooler than this year, and 1929, 1946 and 1949 were similar to 2011.

The abnormally low temperatures were largely the result of the strong 2010-11 La Nina event. Of the five coolest autumns across the country since 1950, four have occurred during or following La Nina events.

This is because increased cloud cover reduces the amount of heating sunlight that reaches the ground.

BOM confirmed last month that the 2010-11 La Nina event had ended, with the climate indicators of the El Nino-Southern Oscillation having returned to average levels.

Most climate models suggest the Pacific Ocean will continue to warm during the coming months, with neutral conditions likely to persist through winter.

No one can predict what will happen next summer. It is possible, though considered unlikely, that another La Nina weather patter could form, which could bring a repeat of last year's flooding rains in eastern Australia.

Nor is anyone able to predict whether the early rains that soaked the WA wheat belt are a sign that things have returned to normal.

For farmers such as Brian Cusack, whose family has farmed the flat plains of Narembeen about 300km east of Perth for the past 100 years, the breaking of the dry this year has been confirmation that it is best to back long-term experience.

Cusack dry-seeded his canola and wheat crop in anticipation of rains arriving on Anzac Day, as the old-timers said they would.

According to BOM in Perth, the first solid rain in Narembeen this year, measuring 9.7mm, fell on April 24, the day before Anzac Day.

In typically rural fashion, Cusack says there were storm clouds in the storm clouds. The rain had been patchy, he says, and 400ha of canola had to be resown because the first rains included hail that hammered the earth too hard for germination.

But overall, Cusack says, things are looking like a normal year, despite BOM forecasting a drier than usual winter. "But they have been wrong so many times before; we will just have to wait and see what happens," Cusack says.

Glenn Cook, WA's BOM manager of climate services, says the bureau has "learned from bitter experience" that good rainfalls early in the season are no guide to what may happen later. WA's rainfall patterns have been changing since the 1970s and many believe the shift is a result of climate change.

According to Karl Braganza, BOM's manager of climate monitoring at the National Climate Centre, before 1970 WA had the most reliable winter rainfall in Australia. But this had reduced by 15 per cent to 20 per cent.

"It would have to rain consistently for a few years to say we have come out of the drought period of the early 1970s," Braganza says.

"The real impact of the drought has been on the water storage. There may have been a 15 to 20 per cent reduction in rainfall but that translates into a 60 per cent reduction of water storage because it is soaked up by vegetation."

Cook says the state's rainfall has been particularly unreliable for the past 10 years. "Rainfall in April, May and June has become much less reliable and declined significantly over the past 40 years," he says. "Even though there has been rain this season it is still not above the recent average.

"Whether it has broken the drought depends on people's circumstances. A lot more rain is needed to fall before water storages and dams are restocked to an adequate level."

Cook says the end of the La Nina pattern in the Pacific Ocean is probably not linked to what is happening in the west. In fact, La Nina is usually responsible for wetter conditions in the southwest of WA, but that was not the case last year.

"The climate has changed," he says. "The relationships that were there are no longer there. Our understanding of climate drivers and the interplay between different drivers is still in its infancy. Those relationships that were understood appear to have changed in the past 20 to 30 years."