Adelaide - Daryl Impey is chasing a third straight victory in Australia's Tour Down Under from Tuesday, but the South African faces an uphill battle against past winners Richie Porte and Rohan Dennis.

Forecast temperatures for this week's race are mild and significantly lower than previous years, a relief to organisers, who said they were working to ensure the route was safe after bushfires scorched the Adelaide Hills region last month.

Mitchelton-Scott's Impey hung on up the torturous Willunga Hill to become the first cyclist to win back-to-back titles in last year's UCI season-opening World Tour event.

"It's harder because you have a target on your back, but when your form is good enough, it's still down to who has the best legs in January," said Impey before the race.

His chances for triple success hinge on a climb into the small town of Paracombe for the third stage finale, along with the demanding double ascent of Willunga that closes out the race in stage six.

"Paracombe (stage three) is tough, and it will test me, as well as many other rivals similar to me, so we'll need to wait and see," Impey said.

"For me, that day's going to be a huge decider in the overall winner. Overall, it is a race that's more suited to climbers, so it'll be tougher for guys like me."

Porte, the 2017 winner and four-time runner-up, is a noted Grand Tour climber and will be suited by the tougher course along with fellow Australian Dennis.

"It's going to be a hard race this year, and it probably is going to be the hardest edition of the race," said Porte.

"Daryl's done a fantastic race in the past two years, and you can never rule him out," he added.

"But I think this year definitely is going to be more of a climber's race. Fingers crossed, anyway."

Dennis is the world individual time trial champion and 2015 race winner. He recently signed a two-year deal with Britain's Team Ineos, formerly Team Sky.

The 2020 peloton boasts another two past overall winners: Andre Greipel of Israel Start-Up Nation and Astana's Luis Leon Sanchez.

Stages two and three will take teams and spectators through areas where properties were destroyed in recent bushfires, which also killed one person and injured other.

"We've been working feverishly to make sure that the route is safe and lots of tree clearance and some minor road repairs have been done," Adelaide Hills Mayor Jan-Claire Wisdom said.