Sydney needs 'a metre of rain' to break drought

At this time last year Woronora Dam was sitting at 54.9 per cent capacity. Fast forward to this week and storage levels have fallen more than 16 per cent to be sitting at 38.7 per cent.

Sydney's dam levels are falling so quickly the city would need the equivalent of a metre of rain and a major deluge to break the dry spell.

The Sydney Morning Herald reports that details of the state of Sydney's catchments were circulated to government agencies this month as NSW braces for increasing stress on water supplies.

"It will take approximately 1000 millimetres of rain to fall over the course of a year in order to break the current drought in Greater Sydney, including an intense rain event of 200 millimetres over 1-2 days," the government document states.

"The annual average is 850 millimetres."

Woronora Dam storage snapshot. Graph: waternsw.com.au

Woronora Dam storage snapshot. Graph: waternsw.com.au

Sydney's dams are 48 per cent full, down more than 10 billion litres over the past week.

The weekly drop of 0.4 percentage points would have been more without the 250 million litres being produced daily by the desalination plant at Kurnell.

"Greater Sydney is in drought and dam levels are dropping faster than they have in decades," a spokeswoman for Sydney Water told the Herald.

"This ... is around 50 per cent greater than the Millennium Drought," she said, adding that storage levels had sunk from 90 per cent to below half full in about two years.

Governments have been scrambling to respond to a sharp reduction of rainfall even as evaporation rates have increased with record temperatures.

Cataract Dam near Wollongong is the lowest among the Greater Sydney network at just 27 per cent full. Picture: Chris Lane

Cataract Dam near Wollongong is the lowest among the Greater Sydney network at just 27 per cent full. Picture: Chris Lane

In NSW during the first nine months of 2019, rainfall has been half the average while daytime and mean temperatures are running at the hottest on record.

"The Bureau of Meteorology's climate forecast indicates no foreseeable signs of reprieve from current drought conditions, with warm and dry weather predicted," the Sydney Water spokeswoman said.

"Based on these forecasts, the drought is therefore unlikely to break within the next year."