The Indian Ocean Dipole (IOD) has moved into a positive phase, increasing fears of a severe bushfire season.

The Bureau of Meteorology says El Nino remains strong, and its drying effects could now be enhanced by the positive IOD.

The IOD – an ocean and atmosphere phenomenon – has exceeded a +0.4-degree warming threshold for the past eight weeks and is at levels not seen since 2006.

CSIRO climate expert Wenju Cai told insuranceNEWS.com.au the two weather conditions combined make the south and east of Australia “vulnerable” to bushfires.

Dr Cai says positive IOD events in the springs of 2006-08 preceded the Black Saturday bushfires of 2009, and the Ash Wednesday fires were also preceded by a positive IOD in the spring of 1982.

He says the Indian Ocean is usually a “major moisture source” for south and east Australia in winter and spring, but a positive IOD results in rainfall going to the western Indian Ocean instead.

“In September rainfall was half of the normal rainfall,” Dr Cai said. “If it’s dry, it’s easier to heat up, because you don’t get evaporated cooling.”

However, the bureau says sea surface temperatures across the whole Indian Ocean basin have been at record warm levels, and this can result in increased rainfall.

“[This appears] to be offsetting the influence of [the IOD and El Nino] in some areas,” it said.