Lismore floods show 1-in-100 year mapping is ‘outdated’ and homes are not as safe as we think

Homeowners are being warned 1-in-100 year mapping is now “outdated” and people’s homes are not as safe as they thought they were.

The severity of the Lismore floods may have exposed potential flaws in modelling for climate change impacts – with homeowners warned that 1-in-100 year mapping is now “outdated”.

Climate Valuation chief executive officer Dr Karl Mallon, whose company specialises in assessing climate change risk for people’s properties, says it will re-evaluate its ratings after the latest extreme weather hit the New South Wales city harder than expected.

Dr Mallon said Climate Valuation gets data from global flood modelling specialists from the United Kingdom and Sweden – which also supply data to insurance agencies in Australia – that predict where water will flow by looking at rainfall and land topology.

This data indicated the recent flooding event in Lismore would be considered extremely rare – not just a 1-in-100 year event, more like a 1-in-1000 year event.

“That leaves us with two possibilities,” Dr Mallon told news.com.au.

“One, is that it genuinely was a rare event and those houses were somewhat unlucky to be in the wrong place and the wrong time.

“Or climate change is effecting the probability of these events and this suggests that all risk management communities need to reassess their view on the likelihood and severity of these extreme flooding events.”

Dr Mallon said there was no question mapping of 1-in-100 year flooding events used by councils was already out of date because of climate change. It’s been confirmed Australia has already warmed by 1.4C, higher than the global average of 1.1C.

“The physics are simple, as the Earth becomes hotter, more water from the ocean and land is evaporating and being held in the air,” Dr Mallon said.

When a rain event occurs there’s more water that can fall down, meaning flood events on average will be more frequent, and more severe and damaging.

“For every degree of warming, the atmosphere can hold 7 per cent more water, so we already have an atmosphere that can hold more water,” Dr Mallon said.

“The maps are already out of date.

“In the industry that’s a given and I don’t think anyone disagrees with that.”

This is not good news for homeowners who often rely on these maps to assess risks to their properties.

Last year, news.com.au highlighted the risk to homeowners, with many not properly informed of the potential climate change impacts on their properties.

Dr Mallon said people observing the devastation from other states should not be complacent. Some properties flooded in Lismore had never been inundated before.

“It’s only a matter of time with climate change and the risks escalating,” Dr Mallon said.

Lismore flooding hit areas that had never been inundated before. Picture: Toby Zerna

What homeowners can do to assess their risk

People buying homes are advised to get a climate check and to think about resell value.

“Insurance might be affordable now but will it be affordable at the end of the mortgage?” Dr Mallon asked.

He said many banks were also beginning to consider climate change risks to property, and could be a source of information. “It’s only a matter of time before they stop offering mortgages on high risk properties,” he said.

Dr Mallon also advised making a call to local councils, which could uncover concerns beyond those provided on risk certificates.

“Council might have more information if you go and have a chat with them,” he said.

Climate Valuation provides information about climate risks on individual properties, with a basic summary provided for free.

In general, Dr Mallon said its modelling about what areas were at risk, even down to individual streets and addresses, had predicted which properties would be impacted by recent flooding.

“I dare say some of the damage is no surprise to the insurance industry and it’s a bit of a shame that people have been caught out and there was loss of life when we do know which houses are at risk,” he said.

“We need to learn from this and it would be silly for us to go through this again.”

Flooding damage in places like the Sunshine Coast, Brisbane, Gold Coast, Northern Rivers and even in parts of Sydney, had lined up with expectations.

But Lismore was different and Dr Mallon said it would now adjust its risk ratings to reflect the possibility climate change impacts could be worse than flood modellers have estimated.

“We could be underestimating the likelihood and severity of these events,” Dr Mallon said.

Climate Valuation analysis has estimated damage costs for private property across Australia will rise by a staggering 257 per cent, from an average of $7 billion in 1990, to $25 billion in 2100. This does not include the cost of damage to public infrastructure.

The hazards that are expected to contribute most to this increase are flooding, coastal inundation and extreme wind including cyclones.

Dr Mallon also noted that describing something as a 1-in-100 year event did not mean it only happened once every 100 years, it means there is a 1 per cent chance of it happening each year. For a 1-in-1000 year event, there’s a 0.1 per cent chance.

Analysts are reassessing their modelling for which properties could be impacted in future extreme weather events. Picture: Jason O'Brien

‘People are largely alone in this situation’

Dr Mallon warned much of these climate risks will be borne by individual homeowners, and he believes people selling homes will increasingly have to convince homebuyers they’ve made their property resilient.

“What we really want people to realise, is they should take a good hard look at what they’re seeing in newspapers – people are largely alone in this situation,” he said.

“A lot of properties are underinsured so won’t get enough money to rebuild or refit their properties to the way that they were.”

Northern NSW flood recovery co-ordinator Mal Lanyon told ABC radio’s AM program on Wednesday that “potentially thousands” of properties were uninsured.

“We’re seeing governments step back and say it’s not their fault,” Dr Mallon said, pointing to recent comments from Australia’s disaster relief boss Shane Stone that people who choose to live in flood-prone areas shouldn’t blame the government for losing their homes.

“They are essentially implying that people should be aware of these things,” Dr Mallon said.

People are largely being left alone to deal with the aftermath of floods. Picture: @thesherwoodhotel/Instagram

While Dr Mallon agreed people shouldn’t be moving back into some properties located in flood prone areas, and that other buildings needed to be upgraded, he also believes the state government bore a significant amount of responsibility, noting state planning and building codes had allowed these properties to be built and traded.

“These properties got planning permission, someone has been taking the stamp duty and rates from these properties,” Dr Mallon said.

“It’s not appropriate for them to step back now when the property has been wrecked and is dipping in value.”

Dr Mallon said support needed to be provided for people to exit high risk suburbs or there should be grants so people could upgrade their properties and make them insurable.

He said there were also lots of things people could do to make their properties more resilient such as rebuilding with more advanced materials, using cement board rather than plasterboard, and solid insulation rather than fibre versions.

Flood proof doors and windows – which have become popular in the United Kingdom – can also help hold back water, while walls or gates around the perimeter of people’s properties could stop water of between 1-2 metres high.

Homeowners could also consider building floodable garages downstairs and locating living areas up high.

“Most properties experience small floods but even if it’s 0.5m, if the water gets into the house, the damage that’s done is huge,” Dr Mallon said.

Flood proofing measures would make a lot more houses insurable and while they were not cheap, they were more affordable than a wrecked house.

“Spending $50,000 on a protective wall or changing materials is better than having a $500,000 home basically wrecked,” he said.

Dr Mallon advised people to take a “good hard look” at what they would do if their property was susceptible to flooding.

“Make sure your insurance covers flood and then think about investments you could make if flooding did mean you’d get 0.5-1 metres of water into your house,” he said.

Originally published as Lismore floods show 1-in-100 year mapping is ‘outdated’ and homes are not as safe as we think