Wildfires are on the rise and investigators work the ground to try and figure out how they start. Photo: CHRIS SKELTON
When faced with hundreds of hectares of charred land after a massive wildfire, sometimes it takes a fire investigator on their hands and knees with a magnifying glass to find out where and how it started.
Fires destroy their own evidence but there are still enough clues to work out what happened if you know what to look for.
Fire and Emergency specialist investigator Craig Chambers said every fire needed to have an origin and a cause determination, and that was where fire investigators came in.
Specific factors such as the angle of the char and the way leaves in the area curled could indicate where and how the fire travelled, he said.
Chambers was involved in the lengthy investigation of the massive fire on Christchurch's Port Hills in February 2024. The blaze burned through 700 hectares of land, forced more than 100 properties to evacuate and destroyed a container home.
Investigators managed to narrow down where the fire started to an area of about five square metres on private properly near the Worsley Track. However, they were not able to determine the cause.
Chambers said the number of wildfires each year was continually increasing.
"Data that we have shows incrementally year upon year there's more and more. In the last five-year average there was a total of 4683 wildfires that burned 8000 hectares. If you go back to the 10-year average there was 4400 fires affecting 5900 hectares," he said.
This made the work of investigating them increasingly important, he said.
"That's our drive, working out where and why so that we can inform our communities... what will reduce the risk and chance of fire."
Canterbury has seen a spate of wildfires over the summer.
In a single week in December, crews were kept busy with wildfires at Bridge Hill, Kirwee, West Melton and Burnham, which threatened properties and burnt through hundreds of hectares of scrub and forest.
There have been multiple other fires in recent days.
Fire and Emergency community risk manager Craig Chambers. Photo: Supplied
Chambers said 97 percent of wildfires were caused by human activity. He said arson was rare, but it was a consideration investigators needed to have when looking at the cause of a fire.
"Was it a lightning strike? Was there a roadway or railway beside it, hot metal? Was there human activity in and around? So what was going on was somebody out in the heat of the day mowing the paddock, hit a rock, hit a spark, that sort of stuff," he said.
Witness evidence was valuable, but it was just one part of the equation, Chambers said.
"If we've got any witnesses that say 'I first saw it in this area' that's very handy because we can narrow it down. Imagine there's a 500 hectare fire and we have to start on the boundary of that 500 hectare and come in. If there's no witnesses we would start out where the most damage has occurred," he said.
"People do perceive things differently. It's really intriguing how people see one thing but another person sees it slightly different then when we get there and have a look around and put the fire science and indicators together how that aligns with or not with what they say."
Chambers said investigators developed hypothesise theories on how the fire might have started, and then they tried to disprove them.
"If we can't disprove a hypothesise then that's what we say is the cause. It's not about proving the theory, it's about disproving the theory," he said.
He said it could be frustrating to not end up determining a cause for a blaze - like in the case of the February Port Hills fire - but that did not happen often.
"We got it down to an area we're happy with, still undetermined but it's one of those things, sometimes there's just not enough information for us to 100 percent put our hand on heart and say it's this due to this," he said.
"The undetermined side of things is semi-rare, so we do gather enough data to compliment our messaging and our risk reduction activities. Every fire we go to whether we can or can't determine a cause we still learn heaps and heaps about fire development, travel, the weather systems, the fuels that are impacted and all that."
Chambers said everybody could take steps towards reducing the risk of wildfires.
"It's not always an agency's responsibility to manage their risk, property owners have a responsibility as well... Nine times out of ten it's as simple as keeping the grass around structures and anywhere you're doing activities really short, green if possible it's not always possible, limbing trees so that if a fire comes up to a tree through grass fuels it can't climb up the tree because there's no branches for the fire to grab a hold of."
Fire and Emergency urged people to take care when doing any activities that could cause a spark and to do these in the cooler parts of the day.
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