03 December 2009

Welcome to Summer

With the beginning of December also comes summer which is peak bushfire season in southern Australia. If it is anything like the spring in terms of weather it will be a bumpy ride.

In particular, QLD and NSW have seen unusual levels of fire activity over the spring. In QLD, abundant rainfall the previous two years produced abundant fuel. This year has seen development of an El Nino in the central Pacific and two heat waves of unprecedented magnitude to much of eastern Australia. Extended periods of significant fire activity were seen in much of the east, with the city of Rockhampton being directly threatened. Across the season, northern regions of Australia, including the Top End, Cape York, the Kimberley and such, observed normally high amounts of fire activity. More recently, unusual fire activity has been observed in central NT. Fires continue in this general area.

And who can forget not just one, but two large dust storms.

The latest extreme heat event has broken, and with it the fire threat has eased temporarily. A few fires linger in NSW and southern QLD, but the break in the weather has allowed firefighters to acquire and maintain control over the most threatening (to human values...) fires.

That said, the image, from Aqua MODIS shows northern QLD on 2 Dec 2009. Widespread fire activity is still noted, particularly on the Cape York Peninsula. Conditions are hot and dry; the wet season has yet to start in earnest. But the winds are not particularly strong, so fire dangers remain lower than they otherwise could be. Whatever fuel is present is undoubtedly ready to burn; grass is cured, forests are dry.

Historically, the wet season onset is late during El Nino years. Current observations suggest that the active phase of so-called MJO, frequently a trigger of the monsoon in the north, has passed our longitude in the last week or so and hence not expected for a few weeks at least. That suggests that conditions could remain ripe for fire in the north for several more weeks, perhaps even into January in a worst-case. Conditions remain dry throughout the eastern states, meaning any hot, windy day will easily see a rise in fire dangers in those areas. The moderate-strong El Nino historically means a bad fire year for southern and eastern Australia, suggest the need for special caution throughout the upcoming season.

No comments: