Chris de Freitas: Wildfires an underestimated effect of drought

Living in a house surrounded by bush can be risky. Photo / Paul Taylor

A spell of the driest weather for years has parts of the North Island on drought alert. Cracks in the soil, dead grass, vegetables half their normal size, dry forests and fire alerts, are just some of the symptoms of the region's drought.

The dry weather is due to lingering high pressure cells that do not allow rain-producing systems on to the region.

According to Niwa, drought risk is expected to increase in all areas that are currently already drought-prone, under both the "low-medium" and the "medium-high" future climate change scenarios.

For the Auckland and Far North regions this means the current one-in-20 year drought could occur on average between once every five years and once every 10 years in the 2080s under the "low-to-medium" climate scenario.

Reliable prediction is important because it affects our drought risk assessment. Risk is defined by Emergency Management Australia as the perceived likelihood of given levels of harm, damage or danger.

The impact of drought is often perceived as presenting the greatest risk to agriculture. But our greatest risks come from situations that are not beyond our control, and mostly where population concentrations are greatest. Take the risk of wildfires for instance.

A wildfire is a large, destructive fire that spreads quickly. It starts in grasslands or forests fuelled by dead or dry vegetation. The cause might be natural (lightning), accidental or deliberate, but preconditions are weather and climate.

They are key components of the fire environment and are fundamental elements of wildfire behaviour and fire danger, in particular, strong winds, high temperatures, low humidity and drought. An appreciation of the role of these is essential to assess and manage the risk of fire weather and fire danger.

Living in a house surrounded by bush can be picturesque and peaceful, but it can also be risky. As the suburbs expand into the hills, more people and property may be at risk.

Recent events have proved that fire is one of the biggest threats to communities on Great Barrier Island, much of which is covered in flammable manuka and pine.

The natural hazards literature suggests that surprisingly few people realise that when they move to the edges of the bush, they move into the province of wildfires. According to the US Institute for Business and Home Safety, one-third of US homes are located in the so-called "Wildland Urban Interface".

These are areas that combine housing developments within a natural setting of trees and vegetation. Homes in these areas have become common casualties of hard-to-control wildfires. As far as I know, there are no comparable statistics for New Zealand as a whole.

According to the Greater Wellington Regional Council, about 20 per cent (165,500ha) of land in the Wellington Region is at high-to-extreme risk from wildfires.

One can only wonder what it is in parts of the greater Auckland region, especially in the potentially high-risk forested areas to the west (Waitakere Ranges), south (Hunua Ranges), northwest (Woodhill Forest), north (Mahurangi Forest) and east (Gulf Islands).

Climate is a key feature of New Zealand's physical environment. It is a free natural resource base for generating national income that can be exploited to enhance human wellbeing.

It also underpins the bucolic image of green pastures, gleaming lakes, flowing rivers and rain-fed agriculture that collectively form a large part of the foundation on which the New Zealand Pure brand rests.

But there is no such thing as a constant climate. It's always getting drier or wetter, warmer or cooler. And an enduring feature of climate is its changing patterns of variability and therefore changing risks. The importance of this cannot be overstated given that climate sets limits on certain human activities. It is crucial that this is taken into account in environmental policies and management strategies.
Chris de Freitas is an associate professor in the School of Environment at the University of Auckland.