31 Mar 2014

Fire, flood, rising sea threaten future

6:32 pm on 31 March 2014

Wildfires, more frequent and severe floods, and higher risks to coastal infrastructure due to rising seas are just some of the impacts New Zealanders can expect from climate change in coming decades.

The Intergovernmental Panel on Climate Change on Monday officially released its report on impacts, adaptation and vulnerability, which identifies eight key risks that will affect New Zealand and Australia as temperatures continue to rise in step with increased greenhouse gas emissions.

Storm surges are a signal of future sea rises.

Storm surges are a signal of future sea rises. Photo: PHOTO NZ

The report is the second part of the IPCC's Fifth Assessment - the most comprehensive assessment of the world's vulnerabilities to climate change. It warns that adapting to future impacts in this region could mean having to translocate industries and giving up on protecting certain areas from sea level rise and excessive heat.

Wildfires are expected to cause damage to settlements and ecosystems, economic losses and risks to human life in many parts of New Zealand as a consequence of drier and warmer conditions.

One of the lead authors for the report's chapter on New Zealand and Australia, NIWA climate scientist Andrew Tait, says wildfire is already a major issue in Australia, but New Zealand now also faces a higher risk.

"Large areas of the country which have traditionally not been high-risk areas, Southland and Waikato, for example, due to a warming environment leading to more evapotranspiration and a drying of the soils and the vegetation are going to be more at risk from wildfires as we move through the century."

Droughts will be more intense.

Droughts will be more intense. Photo: PHOTO NZ

The chapter's coordinating lead author, Agricultural Greenhouse Gas Research Centre deputy director Andy Reisinger, says wildfires could be more destructive in New Zealand's as our native forests are not adapted to it.

"The other point is of course that much of how New Zealand has dealt with rising greenhouse gas emissions so far was to plant forestry that absorbs carbon from the atmosphere, and it's ironic that there's now a rising risk in releasing such stored carbon in wildfires."

Rainfall predictions for New Zealand are for more rain in the south and west, and drier conditions in the north and east. Andrew Tait says the main pattern is associated with a likely change in westerlies over the country, which are projected to increase mostly in the spring and in winter.

"Some of our large South Island catchments have their headwaters in the Alps where we are expecting mean rainfall and the extreme events associated with warmer temperatures to increase, leading to larger floods, in the order of 5 to 10 percent larger by the middle of the century, to what we've been used to in the past."

The Waikato's Waipa River flooding below Te Kuiti.

The Waikato's Waipa River flooding below Te Kuiti. Photo: PHOTO NZ

Sea level rise is expected to reach about half a metre by the end of the century under low-emission scenarios, but Dr Reisinger says even that will be a challenge for New Zealand, with most of our cities and infrastructure built on flood plains and near river mouths.

"There is scope to adapt, but it would require what we call transformative adaptation, which simply means giving up protecting everything but deciding that some areas cannot be protected and we have to think about shifting some communities away from the coast over time. And that would mean major social upheaval."

Warmer winters

There will be some benefits from climate change for New Zealand. Warmer winters will mean lower heating bills and might reduce winter illnesses, forest growth is expected to increase, and some parts of New Zealand can expect stronger spring pasture growth.

An increase in heat waves, constraints on water resources and loss of agricultural production represent three risk areas that apply to both countries, but will have a more immediate and more damaging impact in Australia.

For example, the Murray Darling Basin could lose 70 percent or more of its current food production on a regular basis towards the end of the century.

Two other key risks - the loss of montane ecosystems and changes to the structure of coral reefs - apply only to Australia.

Regional average temperatures in this region have already increased by 0.9 degrees over the last century, and sea levels have risen by 20cm - and the report predicts this will continue.

"It's virtually certain that the region will continue to warm throughout the 21st century and there the projected changes are between 1.5 degrees more for the most stringent global scenario for reducing greenhouse gas emissions up to more than 4 degrees warmer than at present," says Dr Reisinger.

A summary of the report

Ironically, the nation's "Kyoto" forests - planted to store carbon - will face higher risks of wildfire.

Ironically, the nation's "Kyoto" forests - planted to store carbon - will face higher risks of wildfire. Photo: PHOTO NZ