Jamie Morton is the NZ Herald's science reporter.

NZ seeing 'the worst' of fire season

Helicopters with monsoon buckets drops water over burning pine trees near Waimarama Rd, south of Hastings, this week. Photo / File
Helicopters with monsoon buckets drops water over burning pine trees near Waimarama Rd, south of Hastings, this week. Photo / File

New Zealand is now experiencing the worst of the fire season, a top officer says, with a dangerous combination of high temperatures and low relative humidity creating "trigger point" conditions across eastern hot-spots.

A more extreme southwesterly summer regime has kept much of the North Island's East Coast and vast stretches of Canterbury dried out - and with plenty of fuel to burn.

As the summer progressed, rain-deprived eastern landscapes had transformed from vibrant green to the colour of golden straw - and cured grass at this stage heightened the potential for a fire to ignite, spread and create flame fronts more than two metres high.

Strong northwesterly winds had also been a major factor in pushing fire severity and danger levels to extreme, especially for the East Coast, where nearly 40 people were this week evacuated during a major wildfire near Hastings.

Read more: Big wet, bone-dry: A tale of two Kiwi summers

Further south, on the edge of Christchurch, more than a dozen helicopters, a plane and 100 firefighters were sent in to battle two massive wildfires, which had torn across more than 700ha since erupting on Monday evening.

The other major blazes that rural fire crews had faced this summer - including major events at Mahanga, Gisborne, Marlborough and Whitianga - also pointed to an East Coast primed for fire.

Outdoor fires are now banned across Northland, Coromandel, the Hauraki Gulf, Gisborne, Hawkes Bay, Marlborough Christchurch, Banks Peninsula and Central Otago.

"We are probably in about the worst of it at the moment," said the National Rural Fire Authority's rural fire manager, John Rasmussen.

"While February is traditionally our busiest month, because it's drier, the wind is not usually bad as it has been this year."

Rasmussen said the authority was concerned that a dangerous cross-over effect in the weather - where temperatures, reaching into the mid-30s in some places, became higher than relative humidity, which was dropping as low as 29 per cent - was creating a "trigger point" for wildfires.

"For us, that's when conditions become critical - and it's when it gets difficult if a fire does start."

Read more: Explained: The summer of our (mostly) discontent

The extreme fire danger also meant fire crews had to be especially careful, particularly when battling blazes uphill and down-wind.

"In some cases, it means they can't actually get in there and do a hell of a lot until something changes: whether it's the fuel, the weather or the topography."

While temperatures are predicted to remain near or above average in eastern areas until April, Rasmussen expected the easing of winds into autumn would help lower the risk.

Serious bush fires this year

Mahanga, January 8:
A major scrub fire scorched 35ha of land, razed property and caused the evacuation of baches and homes in the Hawke's Bay community.

Mt Horrible, Arthur's Pass, January 9:
A fire scorched about 100ha of land, taking five helicopters to tackle and closing nearby State Highway 73. The blaze, which reignited days later, was estimated to have cost $150,000.

Whitianga, January 17-18:
A wildfire ravaged 70ha of land on a peninsula, wiping out nearly all of the Wilderland Sustainable Community, along with two other residents' homes.

Wither Hills, Marlborough, January 14-15:
A fire that broke out on the banks of the Taylor River, next to Wither Hills Farm Park, came within 5m of a subdivision, causing 60 homes to be evacuated for a time. Six helicopters and 10 fire appliances were used to battle the blaze.

Glenorchy, January 11:
A devastating scrub fire at Rat Point, near Glenorchy and Queenstown, cut power to hundreds of homes and claimed 150ha of native scrub. It was likely caused by a campfire.

Otoko, February 2:
Crews from across the Gisborne area and four helicopters were required to deal with a major scrub fire that scorched 20-30ha of land.

Taupo, February 11:
A blaze destroyed at least 25ha of a pine plantation, stopping just short of the Pureora Forest. It started when recently harvested pine caught alight.

Christchurch, February 13:
More than a dozen helicopters, a plane and 100 firefighters were battling two massive wildfires on the edge of Christchurch threatening city landmarks and homes. The destructive blazes have razed over 700ha since erupting on Monday evening in the Port Hills.

Hastings, February 13:
Nearly 40 people were evacuated, a Civil Defence emergency was announced and 200ha of pine trees were bulldozed for a fire break after a major blaze broke out near Waimarama Rd.

- NZ Herald

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