Dry fuels fanning Port Hills fire
16 February 2017
Firefighters have been battling fires on Christchurch's Port Hills since Monday evening.
Hundreds of hectares of scrub and vegetation have been burnt and nearby residents have been evacuated.
Media Centre asked experts about the conditions fuelling the
fires. Feel free to use the comments below in your reports
and contact the SMC if you need expert comment on other
aspects of the fires. Professor George Perry, Professor of
Environmental Science, University of Auckland,
Professor George Perry, Professor of Environmental Science, University of Auckland, comments:
"Fuels, weather conditions and their interactions drive the behaviour of wildfires. Dead and fine fuels, such as grasses, are highly combustible because they have low moisture content and dry out quickly.
"The vegetation on much of the Port Hills is extremely flammable, especially in those areas where gorse, which is characterised by large amounts of well-connected, dead and fine material, is abundant. Wind and terrain conditions determine fire behaviour, with fire spreading preferentially with the wind and upslope as the flames are tilted towards the fuels.
"The dry and windy conditions in Canterbury have led to conditions conducive to fire spread as fuels are dried and the flaming front pushed by the wind. Shifts in wind conditions pose a hazard to firefighting activities as the fire front can rapidly change speed and direction in ways that are difficult to predict.
"In the longer term, a key question is ‘what vegetation will replace that which has burned?’ A number of invasive plant species, including gorse and pine, are well adapted to regenerate after fire. However, although some of New Zealand’s native species such as mānuka and kānuka are very flammable, few are adapted to fire; this absence reflects the low frequency of fire in NZ’s ecosystems prior to human settlement. Thus, repeated fire favours fire-loving exotic plant species.
"Those species that appear in the aftermath of fire tend to be highly flammable so there is the potential for a feedback loop in which ‘fire begets fire’, a dynamic that may be exacerbated in a drier, warmer future. It is important for New Zealanders to consider how best we might ‘fire-proof’ our landscapes by, for example, using tools such as ‘green firebreaks’."