Flooding danger spreads further in NZ

As extreme weather events become the 'new normal', a new paper warns that it's not just people who live in low-lying areas and on the coast who need to be prepared for flooding.

Thousands upon thousands of people around the world - including in the southern reaches of the American state of Illinois, northern England, southern Scotland and Australia's flood-ravaged Hunter region - have begun 2016 with rescues, evacuations and the expensive consequences of flooding.

Given how much is known about flooding and how to mitigate it, there really should be less disastrous flooding - but instead, there seems to be more.

Waikato University environmental planning professor Iain White is about to publish a paper called Groundhog Day, with Professor Graham Haughton from the University of Manchester in the UK, in which he warns that politicians and planners must start learning lessons from previous floods.

In New Zealand the dangers were highlighted last November in a report by the Parliamentary Commisoner for the Environment, entitled Preparing for Rising Seas. It identified 9000 at-risk, flood-prone homes in the coming decades.

The origins of Prof White's paper came from a conversation with an English colleague in 2014 about flooding taking place in the UK at the time, which had prompted public calls to consult the Dutch - who were seen to be the experts in flood prevention. The low-lying land in The Netherlands (Netherlands literally means low-lying land) requires the country to be heavily flood-proofed.

But their problem is dealing with flooding from the ocean, rather than heavy rainfall causing drainage systems to overflow and rivers to rise and overflow their banks - which was the problem in England, and often here in New Zealand.

"So (the Dutch) are very good at large technical defences that keep the sea out, and this wasn't that risk at all, and this is one of the messages: there's different kinds of risk and they demand different solutions," Prof White told Nine To Noon today

He noticed that there was the same kind of public outcry when the latest flooding happened, with the exact same key points: journalists, politicians and other interested parties all demanded major reviews of policy; doubts were raised about whether flood forecasting policy was correct and about whether there were certain areas being left behind, as well as whether planners had listened to scientists; and whether the flooding was related to climate change.

"It's not just the floods that reoccur, it's the conversations. And this is part of the difficulty as scientists, is that you really want to change things, you want policy to try and adapt to what we call 'the new normality' - and not just have the reoccuring conversations.

"And so it was about drawing attention to this cycle, which isn't just a climatic one but it's a policy one, and it's a political one and it's a journalistic one, and if you recognise that then you've got a chance of really making ground with some of the major policies that might need to change."

The problems particular to flooding in New Zealand were regional and required individually tailored solutions, Prof White said.

"So, for example, parts of low-lying land around the Thames coast (require looking) at certain types of risk, but we've always known that Wellington and Dunedin, they've had floods too so that's different kinds of risk and different solutions but if you take a step back and look at the bigger picture, you really need to start with climate change."

Until global warming was addressed, there would be no reversion to earlier climate patterns, Prof White's paper said.

The majority of climate scientists tended to agree on two things: that recent extreme weather events were unprecedented and that we will continue to experience more of them.

"Now our climate does appear to be changing, there's no real doubt about that whatsoever, we know, we've got records going back from (the) 1800s - so we know that it's getting warmer. 2014 was the warmest year we've had on record, but that was since broken in 2015."

He said it was worth considering just how hot last year was - January 2015 was the hottest January on record, February was the hottest February on record, and so on.

"It was just every month seemed to break new ground."

Overall, 2015 was the warmest year on record - and not by just a small margin.

"It smashed the previous record in climate terms, so if you're trying to picture what that might look like over a large time series, over a hundred, 150 years, you might expect records to be broken every now and again just by a small amount.

"The climate change record for 2015 is like running the 100 metres in nine seconds. It's really smashed our personal best and it means that we need to not just think about the mitigation, about how we might put less C02 into the atmosphere, but also - particularly with countries like New Zealand - how we might adapt, how we might build differently and how we might respond to some of the more extreme events that are happening."

Prof White said the issue around flooding was just exactly "how to listen to the future, and how we give it a voice".

The recent Paris agreement on climate change was a start, he said, but on a national level, the conversations still needed to start about how climate change would mean things would have be done differently in the future.

Sea level rise was one problem that could be relatively easily addressed, as records from the major ports all around New Zealand went back as far as 1899 in some cases.

"So we know that the sea level rise has increased by about 20 centimetres during the last century, so we know that's happened and it's one of the easier floods to understand scientifically, it's just like a bath tub slowly increasing as the global temperature rises - the water tends to expand, you've got a bit more snow melt, more glacier melt and there's more inputs into the system."

Those exact kinds of measurements have been extrapolated so that scientists have predicted that in the next 50 years, sea levels should rise by about 30cm - which Prof White said wasn't too bad.

"You think, well, 30cm, we could just build a few slightly higher sea defences and so on but it's the extremes, it's how does that interact with the king tides, how does that interact with some of the storm events that we get, and how far are those extremes going to get?"

Coastal erosion was one of the hardest problems - one big storm could cause the equivalent of 50 years of erosion in one day.

Flooding from rivers and lakes was a little easier to predict as there are quite visible records.

"You've got old pictures going back and you go near the rivers and you see the big ruler with 'this was the 1945 flood' - there's a good record there."

The data about rainfall went back 100-150 years and was also improving all the time, but predicting the levels of rain and the catchment it could land on was more difficult, because how rain lands changed its behaviour.

Data about rainfall levels actually added up to patterns over a longer period of time until the recent sudden acceleration of climate change, Prof White said. So the cliche of the one-in-100-years weather event was somewhat inaccurate now, as climate change was wreaking havoc with what had been relatively stable systems across decades or longer.

"So while our rainfall varies day to day, month to month, year to year, over this long series, it's assumed to be stationary... (but) we know climate change is making extreme weather more frequent, more severe."

The one-in-100-year event was still useful as a measure of how robust the flood defence systems needed to be, however with the now-seemingly constantly changing climate, the variables were becoming too hard to predict.

"With the sea level rising in and around Wellington, what we might expect to be a one in a hundred year event today, that might happen every year in 50 years' time."

Tackling global warming needed to become a central part of a multi-pronged approach to flood policy, Prof White said, as these extreme weather events become the 'new normal'. And there will be uncomfortable conversations to be had about who pays for flood mitigation.

Listen to the full Nine To Noon interview here: