It warns that if residents do not cut water consumption by more than 50% over the next 20 years, the city will become unsustainable.
The Commonwealth Scientific and Industrial Research Organisation report also warns that temperatures could rise 5C above the predicted global average.
This would leave the city facing an almost permanent state of drought.
Rise in heat-related deaths
With its spectacular harbour and beautiful suburban beaches, Sydney is often portrayed as one of the most desirable cities to live in.
But this report paints a disturbing picture of how life here could be completely transformed by the year 2070, if climate change goes unchecked.
It warns of severe droughts nine out of every 10 years, a dramatic rise in the number of bush fires, and freak storm surges which could devastate the coastline.
Scientists predict that rainfall will fall by 40% by 2070, not only creating a massive water crisis, but producing double the number of bush fires.
Heat-related deaths would soar from a current average of 176 a year to 1,300.
Sydney would come to resemble the harsh, dry and inhospitable conditions of remote inland towns.
The government of New South Wales, which commissioned the report, has been alarmed by its findings.
The state premier called it a doomsday scenario, but one which the city and country had to confront.
Along with America, Australia has refused to sign the Kyoto Protocol, the only two major industrialised nations to do so.
BBCGüncelleme Tarihi: 20 Eylül 2018, 18:16