La Nina won't cut bushfire risk, BOM warns

The Bureau of Meteorology warns Australians they still need to be on bushfire alert despite a slightly higher chance of La Nina rain arriving.

Australians are being warned not to become complacent about this summer's bushfire risk despite a slight increase in the chance of La Nina-driven downpours arriving over large parts of Australia.

Scientists at the Bureau of Meteorology have put themselves on La Nina watch after noticing the emergence of some precursors recently, which have increased the odds of one developing to 50 per cent, which is double the normal risk.

La Nina occurs when waters in the tropical Pacific Ocean cool and push warmer water towards Australia, bringing cloud and and above-average rainfall.

The last one stretched from 2010 and into 2012 and marked Australia's wettest two years on record.

But bureau climate prediction services manager Andrew Watkins says if one develops this year it's likely to be weak and short-lived.

"And given the dry soils in large parts of south eastern Australia and no expectation of widespread rainfall, we've got to be careful not to be too complacent," he told AAP on Tuesday.

"The fire danger will still remain quite high particularly in the south east.

"Weak La Ninas can actually bring heat into southeastern Australia, surprisingly enough, and a weak La Nina doesn't wet up the soils enough so heatwaves and fires, you can't write them off yet."

Most parts of eastern and southern Australia are facing an above-average bushfire risk this summer after one of the hottest and driest winters on record, according to the Bushfire and Natural Hazards Cooperative Research Centre's outlook released in September.

As a result, bushfires could start earlier this season, with warm and dry conditions expected to continue.

Dr Watkins said La Nina's usually developed during winter and spring.

"By comparison, in 2010 we'd already had soaking rains and the soils were already wet, the rivers were reasonably full and we were already in a very strong La Nina event, one of the strongest we've seen," he said.

"But we also had lots of warm water around northern Australia, which helps boost up the rainfall, and we had a negative Indian Ocean dipole, which basically means we had a La Nina in the Indian Ocean as well.

"The ducks all lined up in 2010 but this time (it could be) a weakish, possibly shortish La Nina if we have one."