La Niña increases the likelihood of thunderstorms for flood-prone cities, BOM says, but the risk is higher for some

The days are slowly but surely getting longer and depending on where you are in Victoria you might even see a deluge of pink or white petals peeking through the buds of the cherry blossom trees.

Winter is beginning to say goodbye for 2022 and spring is dying to take its place.

The change of season brings beautiful gardens and milder temperatures, but also brings a greater chance of severe thunderstorms through March, according to the Bureau of Meteorology (BOM).

On January 5th, the regional Victorian town of Creswick was inundated after being hit by a severe thunderstorm.

Figures from Hepburn Shire Council show there was more than $25 million in direct cost losses to the agricultural sector and more than $10 million in damage and losses to the corporate sector.

At least 180 homes were damaged and 55 residents displaced.

Flooding also hit Ballarat, some 11 miles away, but damage was far less than at Creswick.

Creswick was hit by damaging winds during a flash flood earlier this year.(Delivered: Jamie Davies)

Why was this the case?

BOM meteorologist Phoebe de Wilt said the topography and prevailing wind direction could increase a site’s vulnerability to extreme weather events.

“When we get cold fronts crossing the state, northwest winds really come in, and some cities are protected … and others aren’t,” she said.

Ms de Wilt said where thunderstorms struck was more a matter of chance.

A topographical map with Victorian towns highlighted.
Mountainous areas of northwest Ballarat offer the city more shelter than nearby Creswick.(Google Maps)

“Generally, thunderstorms are extremely localized…that means sometimes one city can be hit and a neighboring city can be knocked out entirely,” she said.

“But in general, two neighboring cities will have a comparable proportion of thunderstorms over time.”

Ms de Wilt said compared to Creswick, Ballarat was better sheltered from winds by the mountainous areas to the north-west.

“It’s like water going through a hose,” she said.

“If you have a narrower hose, the water will flow faster through a hose than if you have a wider hose.

“The same goes for prevailing winds.”

A semicircle dial with an arrow indicating a La Niña alert.
BOM declared a La Nina alert last week.(Supplied: Bureau of Meteorology)

What about La Nina?

Last week, the BOM declared a La Niña alert, signaling the potential for major precipitation in the upcoming thunderstorm season.

“Thunderstorms need moisture to fuel the storms, which is compounded by climate forcing mechanisms like La Niña,” Ms de Wilt said.

The other two key factors for a thunderstorm are atmospheric instability and a buoyancy mechanism, which could be an approaching cold front or a low-pressure trough.

Ms de Wilt said if La Niña happened for the third consecutive year, it was also more likely that there could be severe storms in the summer.

A man in a dark hat and sweater is standing in front of a hardware store.
Jamie Davies says he’s not worried about what the warmer months may bring but will be prepared.(ABC Ballarat: Lexie Jeuniewic)

Jamie Davies has run the Davies and Rose Rural Hardware Store in Creswick for 15 years and has flooded the town four times in the last decade.

Mr Davies said he had never seen heavier rain on January 5.

“The rain started around 5 p.m. that evening, then within 10 to 15 minutes it was two inches from the door,” he said.

Mr Davies and his staff had to use supplies including bags of dog food and cement to create a makeshift levy bank to prevent water from entering the store.

Four people set up a makeshift levee at a store during a violent storm.
During the January storm, Mr Davies and his staff were all hands on deck.(Delivered: Jamie Davies)

Mr Davies said he was “generally vigilant but not alarmed” about what the storm season could bring.

“We just have to be ready in case the water comes down the road,” he said.

“Where we’re on the road and at the height of everything, we really can only have one product ready to do a tax bank.”

About Mike Crayton

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