Editorial: Atmospheric river carries threat of more extreme weather

A state of emergency was declared in the Tasman region after widespread flooding hit in Nelson. Photo / George Heard

EDITORIAL

This week the Land of the Long White Cloud slipped, splashed and shivered in an extreme weather event called an atmospheric river.

These waterways of moisture snaking through the atmosphere travel from tropical areas to more moderate latitudes, such as here.

According to Niwa, when they strike New Zealand's steep terrain or another weather event, the atmospheric river bursts and water vapour falls in deluges or as snow.

The consequences this week have been felt across the country. Hundreds of people had to evacuate from homes in Nelson and Buller. Floods cut off the Far North. Downed trees caused road closures. Real rivers have spilled over their banks. The downpours have added to an already wet winter, and landed on sodden soil.

Minister for Emergency Management Kieran McAnulty, visiting Nelson, said: "We were literally watching a hill come down, like pouring yoghurt out of a container".

The calm scientific explanation for an atmospheric river is a world away from the practical experience of floods, slips and deluges at ground level.

In the same way, talk of climate change can seem distant and removed from normality, even though some of its impact is already entrenched in normal life. Scientists say more frequently occurring and extreme events such as heatwaves, droughts, fires, floods, and storms are part of climate change.

In the Northern Hemisphere summer, some famous waterways have been hobbled by the heat. Italy's largest lake, Garda, is at near-record lows, exposing bleached, previously underwater rocks. The riverbed of the Rhine in Germany has been partially exposed. A megalithic monument emerged from a shrunken reservoir in El Gordo, Spain.

People will have to get used to thinking about how extreme weather events are going to affect their lives: how they plan, where they live, what it means for livelihoods, what extra costs are going to be involved, when and where they go on holidays.

Beach locations, towns with rivers prone to flooding, homes with potential for erosion, remote areas that could be cut off are among issues people will have to consider.

Niwa meteorologist Tristan Meyers said: "The science is investigating whether or not atmospheric rivers are increasing for us, but I'd speculate that it's in line with what we would expect from climate change".

He added: "For every degree of warming, the amount of water vapour in the atmosphere can increase by about 7 per cent."

University of Otago senior lecturer in geography Dr Daniel Kingston said climate change was "more than likely playing a role" in this week's weather event.

As the atmosphere warmed, it could hold more moisture, and bring on heavy rainfalls. "Sea surface temperatures around New Zealand are also warmer than average right now, which can further amplify these sort of events."

Insurer IAG, outlining ideas to boost efforts to cut the flood risk from rivers, said climate change was having a huge impact on the sector.

It wants a project started to identify the riskiest areas, has called for building to stop in places especially vulnerable to flooding, and is pushing for more investment in flood protection infrastructure.

Insurer Tower is considering risk-based pricing for coastal erosion, having last year become the first local insurer to assess homes based on individual risk of flooding from rainfall and rivers.

At least 72,000 people live in areas potentially at risk of coastal flooding, and about 675,500 live in places vulnerable to inland flooding.

It seems inevitable that more targeted insurance risk policies will become common with the increasing regularity of disasters and as data on them grows.

Accumulating data about the practical impacts of climate risk is informing planning now for how best to deal with an umbrella threat, that like the pandemic will cut across New Zealand's society and geography.

It may take decades to adapt to current and evolving levels of disruption, with a gap in understanding between what's said about a complex problem and how it is unfolding on the ground.