What the Floods in Fiordland Showed us about Climate Change

New Zealand’s climate is changing, with this year alone providing various climate related challenges for DOC, as well as opportunities to test our adaption and resilience.

By Sam Parsons, DOC Programme Lead – Climate Change Adaptation

Cast your minds back to early February (which does feel like several lifetimes ago).

Back then, much of the North Island was weathering severe drought conditions – in fact it was actually the beginnings of what is now one of the most extreme drought events for Auckland in modern times.

But here in the Southern South Island region, we were having a very different time of things.

An extreme rainfall event occurred over several days, with prolonged periods of heavy and torrential rain about Fiordland and Mount Aspiring National Park.

The heaviest rainfall occurred in and near Milford Sound with at least 380 people stranded and 440km of walking tracks lost.

A State of Emergency was declared.

What happened during the event?

On the 3rd of February 2020, Milford Sound received 566mm of rain in a single day.

This is more than the normal amount for the entire month of February — which is 455mm, in case you were wondering.

Then between the 1^st and 4^th of February 2020, the Milford Sound received 1124mm of rain, which 16% of its normal annual rainfall.

Using NIWA’s High Intensity Rainfall Design System tool (HIRDS) we can see estimate Average Recurrence Intervals (ARI’s), which is the average number of years that it is predicted will pass before an event of a given magnitude occurs.

At Dumpling Hut on the Milford Track the estimated ARI of the daily and 5-day rainfalls were greater than 250 years (i.e. a 1-in-250-year-event) and approx. 170 years in Milford Sound.

In May, Minister Sage announced vital conservation and visitor infrastructure destroyed this severe flood event is being rebuilt through a $13.7 million Budget 2020 investment.

How are these events changing?

Thanks to the NIWA climate change scientists working closely with our DOC team, we have increased our capability for assessing how climate change will impact our work.

An assessment of Fiordland and Mt Aspiring National Parks using climate change projections observes that in the coming decades, the area can expect more heavy rain days (>25mm), more hot days (>25°C) in inland and low elevation areas, and significantly less frost nights (<0°C).

High highs, and low lows, basically. Which isn’t good.

In terms of how climate change will impact extreme rainfall events like what was experienced in February; a warmer atmosphere holds more moisture, so the frequency of extreme rainfall events is ‘very likely’ to increase across New Zealand.

To put that in perspective, Milford Sound’s maximum 1-day rainfall total in the February storm (566mm) had an ARI of 86 years, meaning it’s a 1-in-86-year event.

Under current climate projections, by 2040, this amount of rainfall in a single day will be a once-in-a-55-year event; and then continuing on that path, by 2090 it would be a once-in-a-27 year event.

These numbers are serious, and what we witnessed in February showed how exposed and vulnerable our infrastructure (and biodiversity) is to climate change impacts.

How do we adapt?

To ensure our visitors are safe, our experiences resilient, and our biodiversity thriving — we need to adapt to climate change.

To do this, the climate change information presented in the Fiordland and Mt Aspiring assessment will be used to support the recovery team and engineers in designing and constructing infrastructure that is fit for the future climate it will likely expect.

An adaptive process called Dynamic Adaptive Planning Pathways (DAPP) will also be applied to high value locations like the Hollyford Track to develop long-term pathways for how DOC can manage and proactively adapt the experience to remain resilient in the face of climate change.

We have been building a climate change hub, which is where you can read about the risks climate change poses to conservation, a collection of stories and research; external education resources; and relevant work in the freshwater space.

You’ll hear much more from us on this topic over the coming months. We’re committed to this work, and inaction is not an option.

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Climate change is not a drill, and you can read all about it on the climate change and conservation section of our website.