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Wildfire risk in El Niño – Expert Reaction

Windy, hot and dry weather will be more likely for regions in Aotearoa this summer. So what does this mean for the nation’s wildfire risk?

The climate pattern known as the El Niño–Southern Oscillation, or ENSO for short, was officially declared locally by NIWA this month. With ENSO the country will see dramatic temperture swings and stronger than usual winds. Prevailing westerlies may lead to prolonged dry spells in the north and east of both islands as summer progresses.

The SMC asked experts to comment, especially around what risk wilding pines may pose given cuts to conifer control.

Hugh Wallace, Team lead for Fire and Atmospheric Sciences, Scion, comments:

“It’s difficult to predict all the way until the end of the season, but between now and early December we’re expecting El Niño to cause average or slightly above average fire conditions for New Zealand.

“These increased conditions mean it’s more possible for fires to start or spread, but don’t say whether or not they will actually happen (whether or not fires happen in New Zealand is almost totally determined by the actions of the public).

“The effects of the El Niño are likely going to be seen in the form of erratic and gusting westerly and north westerly winds, with increased fire conditions most likely seen along the east coasts of both the North and South Islands. The east coast is likely to see the greatest increase in potential fire conditions because westerly and north westerly winds are likely to drop the moisture they are carrying in the form of rain or dew as they reach the west coast and cross land, before arriving on the east coast as warm dry winds. These warm, dry winds can dry out fuels like grasses and scrub making them easier to ignite (even a few days after rain) and drive existing fires at high speed. If the strong El Niño westerly winds continue to drop their moisture on the west coasts we could see drought conditions develop in the east later in the summer.

“Rather than focussing on specific at-risk areas, people should think about at-risk conditions and their own behaviours that might cause fires.

“In terms of conditions, most people intuitively understand that hot dry conditions are dangerous, but with El Niño people need to be thinking about windy conditions as well. In these situations, fine fuels like grasses and scrub can dry out enough to burn in hours or days after rain and often catch people by surprise. Windy conditions also can stir up days to weeks old burns that haven’t been properly extinguished (e.g. by thoroughly flooding with water and mixing with hand tools or heavy equipment) so they reignite and escape, usually when unattended. Because these winds are caused by the El Niño and not normal weather patterns, they are also somewhat unpredictable so people may be caught by surprise.

“In terms of behaviours, with the last several years being wet people are likely to be more complacent and not be thinking about fire when they’re doing things like mowing or doing machinery work in flammable areas. With strong winds, fires can often ignite and escape before a person is even aware of them, never mind able to react and start putting them out.

“Regarding wilding pines, from a purely fire perspective (totally ignoring ecosystem impact) pines are most problematic if they are grown close enough to something we care about to put it at risk. This risk can be directly caused by them growing close enough to an object to catch it on fire, or indirectly by growing in along roads and access tracks to make reaching those areas unsafe by cutting off escape routes. This is true of all fuels (native and invasive), just wildings spread and grow faster than most large native plants so take more effort to manage.

“With winds being the big driver of potential fire behaviour early in this El Niño season, fine fuels like grasses and scrub are my big concern in the short term. Fires in fine fuels are easy to ignite, and often spread quickly. If we get an extended drought later in the season, we may see larger fuels like trees become available, but it’s too early to say whether that might happen (though it’s likely in my opinion).

“As a final take-away: Almost all fires in New Zealand are human caused. Even under extreme conditions, fires in New Zealand are extremely unlikely to happen on their own, so how we choose to behave and what we choose to do when it’s hot, dry, or windy has a huge effect on whether a fire starts.”

No conflicts of interest.

Dr Sarah Wyse – Lecturer in Forest Ecology, School of Forestry, University of Canterbury, comments:

“It is important to note that, given the right circumstances, all plants will burn. Under future climates, and more immediately, with the weather conditions predicted for this summer, we are likely to see the conditions that are most likely to encourage fire, namely: hot, dry, and windy conditions.

“That said, we know that the inherent flammability of different plant species differs, with some species more likely to ignite and sustain a fire than others. Within New Zealand forests, flammability is highest among species of our early stages of forest succession: mānuka and kānuka being the obvious examples. As forest matures, different suites of species enter and the microclimate becomes damper and more humid, and therefore the likelihood of fire decreases.  Therefore, early-successional forest and scrub is a higher risk for fire than mature native forest.

“We have made the situation worse with exotic species such as gorse, hakea, wattles, and many pine species. Unlike our native forest trees, these species are well adapted to fires in their native environments and so burn readily and then reestablish well following the fire (eucalypts are a classic example of a fire adapted species that does this). These invasive species can increase the fire risk.

“Wilding pines are an obvious example of fire adapted invasive species, and many pines will release their seeds following a fire when conditions are right for the seedlings to establish. Large areas of wilding pines are also often in our driest sites, where native forests have been lost and are unable to reestablish, such as the Mackenzie Basin. While native scrub and tussock lands will also burn, the pines have so much more biomass and therefore a fire becomes a greater threat to human life, property, and infrastructure.  This is why wilding pine control in these areas is so important. My colleagues at Lincoln University and I have undertaken flammability testing on a large number of plants and have ranked them from most to least likely to burn. Using these data we have provided information to FENZ recommending species that have the lowest fire risk, and highlighting those that carry the highest fire risk and which should be avoided near homes if fire is a concern in your area.

“Although I would reiterate my starting point: that given the right circumstances, all plants will burn.”

No conflicts of interest.

Dr Nathanael Melia, Director & Principal Scientist, Climate Prescience Limited, comments:

“Wilding pines are often touted as an increased landscape wildfire risk. A wilding pine obviously has a greater fuel load than the grassland footprint it covers, and landscapes like central Otago grasslands, where wilding pines are seen as a big issue, are able to exhibit significant fire danger in dry conditions. It’s not just a pine story though; these grass, scrub and bush ecosystems in Aotearoa get flammable faster than pine plantations, grass fires can be really flashy and very dangerous burning extremely hot and very fast. When killing off pines, the flammability is likely to increase as poisoning a pine tree dries out all the moisture and leaves a flammable husk like kindling.

“By far my largest concern around wildfires is where extensive tracts of vegetation abuts dwellings, particularly in hilly areas with a single access/exit route. If this sounds like your place, please visit the FENZ website or phone them up, make a plan, practice evacuations, and monitor drought and fire conditions.

“A simple rule is: if conditions are dry/droughty, and you have a windy day, be alert.”

No conflicts of interest.