Fire risk to double with climate change
AUCKLAND: The extreme fire risk that contributed to this week’s devastating Tasman infernos could more than double by the end of the century, according to climate models.
Firefighters have been battling the blazes ravaging the Tasman district south of Nelson City since Tuesday afternoon, and are expected to face another 48 hours of ‘‘very hard firefighting’’ after the fire area expanded on Thursday night.
It grew to 2000ha on Thursday night, from 1600ha.
Scion rural fire scientist Grant Pearce said the Nelson area averaged about nine to 10 days a year of very high or extreme fire danger, and 16 or 17 in a particularly bad year.
Already this year the region had experienced seven days of very high and eight days of extreme danger.
Fire danger came from a combination of weather factors, including high temperatures, low humidity and wind speed.
Fire managers had reported current fire danger levels were the highest they had seen in almost 20 years, and Niwa’s soil moisture maps showed significant soil moisture deficits across the region, Mr Pearce said.
‘‘The very hot, dry and windy weather over the past month has had a major effect on the drying of forest fuels in particular, including slash and prunings, understorey scrub vegetation, pine needle litter on the ground and organic material in the soil, which all contribute to the amount of vegetation fuel available to burn.
‘‘These dry, elevated fuel loads contribute to easy fire ignition and spread, and to high fire intensities, including crown fires that are very difficult, if not impossible to control, especially in steeper terrain often favoured for forestry plantings.
‘‘Surrounding grass fuels are also dry, but the lower fuel loads mean that fires are usually easier to control once they spread out into these grass areas.’’
These factors were all on course to increase in intensity with climate change, Mr Pearce said.
‘‘Modelling of potential future changes in fire danger indicates that the number of severe fire weather days is likely to increase in many parts of the country,’’ Mr Pearce said. ‘‘This includes the Nelson region, where the number of days of very high and extreme forest fire danger could increase to more like 1213 days per year on average, and maybe 2025 days in the worst years, with climate change.’’
Modelling by Scion last year found that almost all areas of the country would have an increase in fire danger.
The average fire season length would increase about 70% up to 2040, and by about 80% up to 2090.
Although the most fireprone regions of Gisborne, Marlborough and Canterbury would remain the most at risk, the relative increase in risk was highest in Wellington and coastal Otago, where it could double and triple to 30 days and 20 days per season, respectively.
Mr Pearce said measures to counter the increasing fire risk included fire breaks being factored into forestry plans, dams for extinguishing fires quickly, and increasing the availability of firefighting resources in highrisk areas.