Flood Risk to Coburg North when super storm hits Melbourne

1-in-100 flood mapping for Coburg North along Merlynston Creek

I hope you didn’t have too much planned this weekend. It might be good to stay home and see how waterproof your house is when the thunderstorms start rolling in on Friday afternoon, and are expected to keep on dumping torrential amounts of rain all weekend.

Expect flash flooding in low lying areas. Merlynston Creek at Coburg North is likely to flash flood. Take care if you live in the vicinity of the 1-in-100 flood zone for Merlynston Creek, particularly around Sussex Street and Boundary Road. Visit the SES page for Moreland Council for local Flood information.

From my article on Merlynston Creek:

According to the SES in a pamphlet on Flood Information for Coburg North (PDF) published in 2015, the 2003 flood measured 2.61 metres on the Merlynston Creek gauge at Fawkner and caused flooding of up to 1.4 metres on Sussex Street with people needing to be evacuated from cars on Sussex Street.

Climate change is causing more torrential rainfall events to occurr, that increase the risk of flooding events. Increased urbanisation and consolidation of development means more hard surfaces for rain to rapidly run off filling such watercourses as Merlynston Creek and causing flash flooding.

The SES articulated that:

“increased urbanisation means that water can’t be absorbed by the soil and tends to run off towards lower lying areas. During high intensity rainfall (for example, more than 20 millimetres per hour, often during thunderstorms) the volume of water can overwhelm stormwater drains leading to flash flooding. As Merlynston Creek is a very small creek the areas around it can also be affected by flash flooding. Although the water will drain away relatively quickly, areas that could be affected include:

  • Sussex Street, from South Street, across Boundary Road, to
  • Kent Street (and to the east to Adler Grove)
  • The east end of Kent Street
  • Pallett Street where it crosses Bakers Road
  • Allenby Street
  • The cycle path on Renown Street (opposite to Elliot Street).

Heatwaves, Super storms and climate change

Of cause these storms are just weather, but the increase in the long term temperature trend by climate change acts to super charge our weather systems: the hydological cycle becomes more energised. For every one degree Celsius rise in temperatures the atmosphere can carry an extra 7 per cent of water vapour. That means more intense rain, which results in more flash flooding.

This particular low pressure system is drawing moisture from the tropics, so we will also get high tropical humidity for Melbourne, as well as the torrential rain.

Climate change has never been as obvious as it has been over the last few weeks. We’ve seen a record-breaking November heatwave of 15 days of over 30C maximum temperature when the old pre-summer 30C record for Melbourne was 12 days.

Victoria and much of South East Australia is now facing an unprecedented storm with tropical humidity to herald in the start of summer.

This is what climate change looks like!

Scott Williams, Senior forecaster for the Bureau of Meteorology (BOM) when asked to categorise this event on a scale of 1 to 10 on Thursday afternoon responded: “It is going to be pretty close to 10, I think. I will take the punt and say it is a 10 for Victoria.” He warned that it will be worse than the torrential rainfall events in with 100 to 120mm rainfall in 2005 and 2011, both in February, that will paralyse transport infrastructure.

Scott Williams articulated that this will be a double whammy event with Port Douglas type humidity.

“So we are in uncharted territory in terms of predicting this rainfall over Victoria, and the numerical weather models, which have improved vastly over the years, cannot predict the exact outcomes because we don’t usually get this humidity with such a strong low pressure development in this state.” said Scott Williams, Senior Forecaster for BOM.

On Thursday afternoon, the Premier Daniel Andrews issued a twitter thread warning all Victorians of the storm’s impact over the weekend and to take the greatest care.

According to the Bureau of Meteorology, we can expect 100-200mm of rain in the next three days, with up to 250mm in N.E. Victoria.

You can find detailed statewide flood information at this SES site for Victorian municipalities.

Stay dry and take care over the weekend.

Update Saturday morning.

Well central Melbourne dodged the heaviest rain on Friday, about 20mm recorded in the CBD, and over 33mm to 9am Saturday at Essendon Airport. There was a heavy and intense rain burst about 2pm in the northern suburbs including Fawkner with nearly 10mm in 40 minutes (Essendon Airport). Eastern suburbs had higher rainfalls with 76mm at Healesville. Most of the strong intensity rain was on NE Victoria and Great Dividing Range. Strathbogie recorded 176mm. Drizzle today, but more intense rainfall on the radar forecast for Saturday night.

The Climate Council have released an urgent fact sheet on #VicStorms to highlight the significance of the high-impact extreme weather event, with more than triple the amount of Victoria’s average monthly rainfall expected to fall across the weekend, in what has been labelled by the Bureau of Meteorology as ‘unchartered territory’.

With worsening thunderstorms, severe rainfall and flash flooding expected to continue hitting Southeast Australia across the weekend, this briefing paper describes the influence of climate change on extreme rainfall.

KEY POINTS:

* Climate change is influencing all extreme rainfall events. The warmer atmosphere holds more moisture, about 7% more than previously. This increases the risk of heavier downpours.
* Globally, there are more areas with significant increases in heavy rainfall events than with decreases.
* Extreme rainfall events like the Victoria rains are expected to further increase in intensity across most of Australia.
* While there isn’t a significant trend in observed extreme rainfall in Victoria yet, maximum one-day rainfall is projected to increase by 2-23% in Victoria by the end of the century if greenhouse gas emissions continue to rise.
* It is critical that communities and emergency services have access to information about rainfall in a changing climate to ensure they can prepare for the future.

THE INFLUENCE OF CLIMATE CHANGE ON HEAVY RAINFALL:

The heavy downpours across southeast Australia are yet another reminder of how extreme weather events place lives, property and critical infrastructure at risk. Climate change is intensifying many extreme weather events in an atmosphere that is warmer and wetter because of increasing greenhouse gas emissions from human activities, primarily the burning of fossil fuels – coal, oil and gas.
Download the full Factsheet from the Climate Council on the Victorian Storms.

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