SYDNEY (Reuters) - Rising sea levels as a result of climate change will erode Sydney’s iconic beaches by 2050, with some at risk of disappearing, and threaten beachfront homes and commercial properties, a new climate change study said.

A surfer leaves the sea at Bondi beach in Sydney August 14, 2008. REUTERS/Daniel Munoz

Sea levels along Sydney’s coast are expected to rise by up to 40 cm above 1990 levels by 2050 and by 90 cm by 2100, with each one centimeter of rise resulting in one meter of erosion on low-lying beaches, said the Sydney climate change impact report.

“The Sydney region has a heavy density of residential and commercial beachfront developments that may be threatened by either ocean inundation or sea level rise-induced recession,” said the report by the NSW Department of Climate Change.

“Rising sea levels may exacerbate flood risk in coastal rivers,” said the report received on Wednesday.

The report said further study was needed to determine the extent of coastal erosion in particular locations.

But low-lying Sydney beaches such as Collaroy and Narrabeen, which have already been severely eroded by storm seas, and Dee Why and Curl Curl, are most at risk.

Beaches which have a hard promenade, such as Manly, Bondi and Coogee, will shrink as sand is washed away and may need sand deposits in order to survive in further decades.

“In general we expect a recession of the coastline of a sandy beach of about one meter for every centimeter rise in sea level,” said Simon Smith, deputy director-general with the department.

“The coastline will move inward. What is now currently a vegetated dune may become the beach,” Smith said on Wednesday.

“It depends on the beach and the coastal area. Some coastal areas have a rocky foreshore and 40 cm does not make much difference. Some beaches are very deep and high so the beachline will retreat, other beaches are very low-lying and they are up against higher landforms behind them, they will become narrower.”

The Sydney Coastal Councils Group, which represents 15 local authorities and some 1.3 million people, has launched a study of “beach nourishment,” which involves building up shorelines and beach dunes with sand to combat future rising sea levels.

Being a coastal city, some of Sydney’s most important infrastructure is built on its foreshore, and may be affected by rising sea levels. Sydney international airport is built on the edge of Botany Bay, with a runway jutting out into the bay.

“Most of the state’s infrastructure was built with a provision for half a meter of sea level rise, but the individual asset owners are already looking to see if they need to make a change in their asset to prepare for the future,” said Smith.