10 Mar 2021

Extreme weather events predicted for Otago in long term - climate change report

9:28 am on 10 March 2021

A milestone report detailing the risks that climate change poses to Otago including widespread flooding will be tabled this afternoon.

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Flooding in Clutha. (File photo) Photo: RNZ

The Otago Climate Change Risk Assessment found that in the long-term, climate change put the region at risk of an increase in intense rainfall events, drought, coastal erosion and inundation, and more extreme heat days above 30 degrees Celsius in Central Otago.

The report also projected major implications for communities and the economy.

It will be presented at the Otago Regional Council committee meeting.

While the key findings are dependent on different time and emission scenarios, they include:

  • Future annual average warming spans a wide range: 0.5C to 1.5C by 2040, and 0.5C to 3.5C by 2090.
  • The average number of extreme hot days above 30C is expected to increase with considerable variability between coastal, southern and Central Otago while frost days are expected to decrease throughout the region. Under one scenario, the number of extreme hot days in Central Otago are projected to increase up to 30 to 40 days by 2090.
  • A slight increase in annual rainfall in Otago is expected by mid-century, spanning up to 20 percent by the end of the century with the largest seasonal increases projected during winter.
  • Extreme, rare rainfall events are projected to become more severe in the future under all four climate change scenarios.
  • Coastal and some central parts of Otago are expected to see a decrease in annual dry days of two to six days with increases of two to 10 dry days per year for many remaining parts of the region by the end of the century.
  • Daily mean wind speed is projected to decrease about the eastern coast and increase for inland areas.
  • With increased emissions, average annual flows are expected to increase across the region by the end of the century.

The direct impact on communities may include increased exposure to hazards - heatwaves, flooding and fires - while the indirect social impacts include disruption to health services, social and economic factors including migration, housing and livelihood stresses, food security, socioeconomic deprivation and health inequality including mental health and community health effects, the report said.

"The effects of climate change will not be spread evenly across the population, exacerbating existing socioeconomic and ethnic health inequalities."

Exposure and vulnerability to climate change risks were largely dependent on where people live in Otago with the majority of the population living in urban areas, the report said.

"It is expected that new vulnerabilities and inequities are likely to emerge as climate change impacts are experienced more widely."

Roughly 15 percent of the Clutha District's population - approximately 2400 people - live on the low-lying parts of the Clutha River delta.

The reports said stopbanks currently protected much of Balclutha and Kaitangata communities.

But the river with its tight bends, high flow volumes and mainly urban use means the failure of those stopbanks pose a significant risk for the community, particularly given the increased risk of flooding, the report said.

"Floods (characterised by the Mean Annual Flood) are expected to become larger everywhere, with increases up to 100 percent in some locations by the end of the century," the report said.

"Extreme, rare rainfall events are likely to increase in intensity in Otago because a warmer atmosphere can hold more moisture."

Many communities in Clutha, Central Otago, Waitaki and the Queenstown Lakes districts are located within a flood hazard area including parts of Queenstown, Glenorchy and Wanaka that have already experienced flooding in recent years.

More than 40 years ago, the West Otago township of Kelso was abandoned after two major floods of the Clutha River catchment in 1978 and 1980. It was subject to frequent flooding.

"Cascading effects of business closure can impact the whole community, and flood or other hazard risk can ultimately cause the closure of a community, as happened to Kelso, West Otago after repeated devastating flooding from the Pomahaka River resulted in a prohibition on any further development in the township," the report said.

"Reducing impacts on business will require forward-thinking adaptation and innovation across multiple levels of business and by multiple actors - including businesses themselves, related service and supply chains, sector organisations, and related public authorities. Collaborative innovation across all sectors can assist climate change adaptation."

The report mentions seven Kāi Tahu Rūnaka who represent the hapū across the region but said more work in partnership with Rūnaka was needed on climate change risk assessments and adaptation planning.

The report identified the need for further collaboration particularly in prioritising risk and action planning if the region is to respond effectively to the findings.

Climate change 'an intergenerational issue'

Otago Regional councillor Michael Laws gave a simple summary when responding to the report's findings.

"It's gonna get warmer, wetter, windier and wilder, and that's pretty much what we're going to tell our community and then they just going to get on with doing what the private sector does best ... which is adapt."

Given its size and significance, councillor Michael Deakin wants to ensure it will shared widely among ratepayers and businesses.

"If I was a fisherman at Moeraki or a tourist operator at Wanaka or a grape grower in the Gibbston Valley, I would want to be able to see this and use its fine grained potential to make decision about the next 20 years for my business," he said.

"Because that's what it enables... they might be positive decisions, they might be decisions to say 'hey, let's get out of here'."

No part of the Otago environment - ecosystems, terrestrial, freshwater, coastal and marine would remain unscathed with all expected to be at extreme risk by 2090 if nothing is done.

The council's operations general manager Gavin Palmer said parts of Otago would be impacted differently.

The report would aid future decisions rather than already have the solutions, he said.

"The first step in taking action is to have an action plan. But you've really got to work out what are we planning for, and so I think this piece of work helps us get hopefully a unified sense across Otago of what the future climate might look like. Because we'll only adapt effectively if we're all planning for the same sort of thing."

The impact of climate change is on many residents minds already.

Simon Paterson co-owns Armidale Merino Stud in the Maniototo Plains, which relies on genetic breeding.

He's in a better position than some other farms in the region.

"We're not landlocked like some other farms could be potentially. If they lose one road that's the only route in and out. I know some other farms around here they've lost a couple of bridges ... just in these last floods. That's definitely added to costs as far as those bridges haven't been replaced yet so they've got a lot of extra time on the road to get to their other farms," Paterson said.

Queenstown Chamber of Commerce chief executive Ruth Stokes said businesses in her area was in a good position to adapt to climate change.

"I think the reality is that for our businesses in operating in an alpine environment that has always been unpredictable means that our businesses actually have a head start over other businesses in New Zealand who perhaps can kick the climate change can down the road," Stokes said.

In 2015, Dunedin was hit with a one-in-100 year flood.

South Dunedin Community Network chair Eleanor Doig said her community was well-aware of the climate change risks.

"We know that a lot of here is at sea level if not yet below it," Doig said.

"So there's a high awareness around here that things are going to change, going to have to change."

She worries that climate change won't hit everyone the same.

"As the situation gets more and more dire, people who can afford to will go, or they will put in pumps and things in their properties and the people who can't afford those things are going to experience increasingly damp houses and increasingly at risk of flooding."

She doesn't want to see solutions dumped on communities, she wants to see collaboration.

Clutha District Mayor Bryan Cadogan said he was certain some communities in New Zealand might need to consider following Kelso's lead.

"Will that happen in the Clutha District? We've got low lying areas ... that have to be ultra conscious of the issues moving forward and I already think that there's that awareness amongst the owners of the issues. Anyone that would do due diligence on purchasing low lying land now, you'd be a fool if you didn't take it into consideration," Cadogan said.

Climate change was the issue of our generation, he said.

"I would really love for an issue that is so large if central government was taking the dominant lead role instead of local authorities because it is a centralised issue. It's an intergenerational issue."

Gavin Palmer said the council was well aware of the flood risks around Otago.

There was work already underway at the head of Lake Wakatipu to see how Glenorchy can adapt to any rises, in the lower Clutha Delta where there was rapid shoreline retreat that was impacting a protective drainage scheme and in South Dunedin which is at risk from sea level rise and flooding, he said.

"Climate change in Otago is a much bigger issue for Otago than sea level rise on the coast and it's much bigger than flood risk, it comes into the areas of biodiversity and all of those other things as well. I think it just means that there's other things that we need to be thinking about when it comes to climate change," Palmer said.

The Otago Regional Council is planning a significant public awareness campaign to ensure residents are kept in the loop about the results.

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