University of Otago geography emeritus professor Blair Fitzharris, who has worked with the Intergovernmental Panel on Climate Change, was commissioned by the Dunedin City Council in 2010 to write the report. He spoke about it at the St Peter's Caversham parish last night as part of The Caversham Lectures series.
Prof Fitzharris identified ''low lying densely populated urban areas, especially South Dunedin'' as one of five ''sectors'' at risk from the projected effects of climate change.
The June flooding in South Dunedin was in keeping with that prediction, he said.
''Recent events, particularly flooding in South Dunedin, is an indicator of what we said was going to be one of the holdable points.''
That kind of flooding would only happen more often with sea level rise, he said.
''We now know that the groundwater level [in South Dunedin] is controlled by the ... height of the ocean, particularly close [to] the shoreline at St Kilda and St Clair.
''So, as sea level rises in the future, the groundwater level is just going to keep rising as well, unless some action is taken.
''And then at the times of the storm, you're going to get a double whammy, [with] the flooding rain and the storm surge.
''So, that's going to make these flooding events larger as the sea level rises, and also more frequent.''
Dunedin could not do much to address the causes of climate change, but it could act to mitigate problems caused by sea level rise, Prof Fitzharris said.
''By the end of the century, we're going to have another 12 mayors, and one of them is going to have a big problem on his or her hands unless there is a series of policies in place,'' he said.
''You've either got to decide you're going to defend against [the flooding] ... or you can say, `well, we may have to rezone'.''
If the land was ceded, sports fields or wetlands could occupy the area, he said.
But Prof Fitzharris knew it would be ''very difficult'', politically, to implement any changes.
''I wouldn't like to make those decisions.''
South Dunedin was not the only part of Dunedin that was low-lying and vulnerable to floods, Prof Fitzharris said. Other sites, including Dunedin Airport, had been badly flooded in the past. Dunedin was far from the only city in the world to be facing sea level rise.
''What's happening in South Dunedin is being replicated, probably a thousand times over around the world.''
