The regions most at risk from climate change in Australia are where most people live, the Climate Institute has warned.
Using data from soon-to-be-published CSIRO research, the institute found the impacts of climate change threatened the major cities of mainland Australia - where more than 60 per cent of the population lives.
The regions most at risk are the catchments of Perth, Adelaide, Melbourne, Sydney, Brisbane and Murray-Riverina.
The assessment, undertaken by the CSIRO this year, was based on climate change impacts, historical rainfall changes, catchment condition and population growth.
"Clearly, there will be high costs of government inaction on climate change - and it will be felt hardest in our major cities," institute chief executive John Connor said in a statement.
"New research by the CSIRO has also shown that the impact of climate change on the length of severe droughts may double or triple in some parts of Australia after 2050.
"Australians will pay the price of government inaction on climate change with higher water and food costs over the coming years."
The assessment revealed drops in these catchments: Blackwood River (WA) down nine per cent by 2030, down 26 per cent by 2070; Brisbane River (Qld) down five per cent by 2030, down 14 per cent by 2070; Hawkesbury River (NSW) down three per cent by 2030, down seven per cent by 2070; Murray-Riverina (NSW) down seven per cent by 2030, down 20 per cent by 2070; Thomson River (Vic) down five per cent by 2030, down 14 per cent by 2070; Torrens River (SA) down six per cent by 2030, down 16 per cent by 2070.
The report's findings should come as a reality check to those calling for less urgent responses to the threat of dangerous climate change impacts, Mr Connor said.
"This report reveals that it is in Australia's national interest to lead on these matters - at home and abroad.
"This is why we need further action to reduce our carbon emissions and to forge international agreement on tougher targets."
