Ku-ring-gai receives some of the heaviest rain in Sydney in May 2025 causing signficant flash flooding. Ku-ring-gai Council has been inundated with calls for help and has responded with advice to residents on how to respond to flash flooding. fallen trees and power outages HERE.

Sydney has recorded intense rainfall (more than 100 millimetres of rain over the past 24 hours) causing severe train disruption. The North Shore Train Line has closed due to flooding on the tracks between Central and Town Hall Stations.

Extremely heavy rainfall has led to flash flooding from overflowing drainage systems – nature strips, footpaths, roads – overwhelmed by the intensity of rain falling. This has also led to potentially life threatening situations, such as fallen trees and branches.  Power lines have fallen leading to power outages and traffic chaos.

This is not new. In March 2009 the Bureau of Meteorology (BOM) recorded more than 110 millimetres of rain falling on North Turramurra and St Ives. The average for the month for Sydney rainfall in February is around 127 millimetres. However, this same amount fell in North Turramurra within a 24-hour period. Read more HERE

Giant wild storm in January 1991 damaged 7,000 homes across northern Sydney. This photo from Ausgrid archive was taken in North Turramurra, one of the worst hit areas

Useful links

• Contact NSW SES 132 500 for storm and flood assistance.
• SES 132 500
• Live Traffic
• BOM
• Ausgrid – fallen power lines ring 131 388. Check Ausgrid outages website.
• NSW Education
• Sportsfield wet weather closures
• For Ku-ring-gai residents who have no power, hot showers are also available at no charge at the Ku-ring-gai Fitness & Aquatic Centre, Prince of Wales Drive, West Pymble.

ABC News Article: What turns heavy rain into a major flood?

By Tyne Logan and Alex Lim — ABC Climate. ARTICLE HERE and BELOW:

What turns heavy rain into a major flood?

By Tyne Logan and Alex Lim — ABC Climate

• Topic:Floods

7h ago7 hours ago

Parts of New South Wales are currently facing some of their worst floods in living memory, as heavy rain — in the order of half a metre over four days — falls across the region.

Houses and shops are flooded, cars submerged and river levels have swollen to record levels.

You’d be forgiven for thinking this is all about the rainfall. It’s crucial, of course. But it’s not the only thing that matters.

Understanding the factors that drive flooding can explain why some places are more impacted than others when heavy rain hits.

Ground conditions

Water, of course, flows downhill, moving via a network of rivers and drainage systems.

Floods happen when rain from across a catchment area moves towards one area and accumulates faster than it can drain away.

But what the rain is falling on can make a big difference.

Four ways water can move

How quickly it can flow into and out of an area determines flood risk.

Rainfall

Surface flow

Absorption

Drainage

ABC News

It can be helpful to think of the ground as if it’s a sponge. How empty it is and how porous it is will determine how much water it can take on.

Albert Van Dijk, a professor of water science and management at the Australian National University, said soil very much behaves like that too.

“The soil has got what’s called an infiltration capacity. And if that’s exceeded, then it starts to run off over the surface,” he said.

Some soils, like sand, are really porous. This means they can drain water really fast, lessening the amount of run-off and the impact of the flood.

A surface like bitumen, on the other hand, won’t drain the water at all.

“That’s a big issue with urban flooding,” he said.

Built environments affect run-off

Soil

Ground compositions (e.g. sand, clay) can have varying levels of infiltration.

Land development

Urban areas are generally less permeable because of paved surfaces.

ABC News

It’s not just the type of surface.

Just like a sponge, the ground can only hold so much water. If it’s already full then any extra water will overflow no matter how porous the ground type is.

Once soil becomes saturated…

…more water will run off.

ABC News

This is one of the main reasons the same location may see different flood effects from the same amount of rain, according to University of New South Wales Water Research Centre director Fiona Johnson.

“The catchment wetness is really the thing that is the most variable from event to event,” she said.

“200 millimetres [when it’s been wet], versus 200mm when it has been very dry, will give you a very different flood.”

Rainfall

Next, there’s the rain itself — not just how much, but how intense and over how long.

Even if the ground has the capacity to absorb all the rain that’s falling from the sky, there’s a limit to how fast it can soak it up.

Just like if you turn the tap on too hard and fast, some of it will overflow.

This is often the case in flash flooding situations, especially in cities where drains struggle to keep up.

An increase in the intensity of short-duration rainfall events is something climate scientists expect to see as the climate warms and the atmosphere is able to hold more moisture.

Warmer air can hold more moisture

It expands, leaving more space between molecules to hold water.

Capacity to hold water vapor

Air expands with temperature

More capacity

Water vapor

ABC News

Already, observations have shown rapid rain bursts over Sydney have increased by 40 per cent over the last 20 years.

Landscape

Other parts of the landscape can play a role as well.

Whether or not the water has a clear run, for example, can also impact how much water makes it to the bottom. Vegetation, like trees and shrubs, can help slow down the flow.

The shape of the land also makes a difference. Steep hills will send water rushing down, giving the ground little time to absorb it, similar to the way heavy rainfall creates floods.

Steep terrain

Surface run-off may absorb slower and/or encounter obstacles.

ABC News

And then there’s what the water is flowing into.

Dr Johnson said in a small catchment, short but heavy rainfall can be enough to cause flooding.

“That’s really hard to plan and evacuate and prepare for because you just don’t have any warning time,” she said.

“Whereas a larger catchment, it’s a couple of days of rain and so you’re kind of going to get a little bit more of a heads up … and also it takes a lot longer for the flood to move from the top of the catchment to the bottom of the catchment.”

Even small amounts of rainfall can accumulate quickly

A narrower creek has less capacity to hold water. Flood waters can rise quickly if rain falls faster than it can flow onwards.

ABC News

All the ingredients are present in NSW

So you can see, there’s a lot that goes on.

All of these factors can amount to a “huge” difference in the outcome of a flood, according to Dr Johnson.

Knowing this, it can be easy to see how the rainfall in New South Wales has turned into such severe flooding.

Firstly, a colossal amount of rain has fallen.

Several locations have received three months’ worth of rain in a matter of days, amounting to a huge volume of water moving across the catchment areas.

Mount Seaview is now sitting at over 900mm of rain for the month, more than seven times the May average.

Similarly, Kempsey is nearing 500mm and Port Macquarie over 700mm.

The rain also fell hard and fast, and then kept coming.

Taree recorded 279mm in the space of just 24 hours on Monday — a daily record for May — followed by another 300mm over the following three days.

The ground was already quite wet and full.

Even before this event began, the NSW north coast had seen plenty of rain during March and April, partly due to a hangover from Tropical Cyclone Alfred.

And, the region is threaded with multiple rivers, which many towns — like Taree — sit on the banks of.

The heavy rainfall has now cleared out of the state’s mid-north coast, shifting south. But the flooding will continue for several days.

Odyssey format by ABC News Story Lab