Behaviour of fire weather indices in the 2009–10 New Zealand wildland fire season

Abstract

The Weather Research and Forecasting mesoscale atmospheric model was used to investigate fire weather conditions during the 2009–10 New Zealand wildland fire season. The analysis considered New Zealand's version of the Fire Weather Index used in the Canadian Forest Fire Danger Rating System, the Haines Index (HI) and the Continuous Haines Index (CHI). This represents the first investigation in New Zealand of the HI and CHI, which rate the potential for extreme fire behaviour or large fire growth based on the lower tropospheric atmospheric stability and humidity. The wildland fire activity during the 2009–10 fire season was typical of New Zealand, and there was considerable spatial and temporal variability in the fire weather conditions. The most frequent severe fire weather conditions as quantified by the fire weather indices occurred to the east of the dividing mountain ranges in both the North Island and South Island, and were associated with the hot, dry and windy north-westerly foehn winds that commonly affect New Zealand. The 36 wildland fires greater in area than 5 ha during the 2009–10 fire season occurred under a range of fire weather conditions, and no correlation was found between the wildland fire size and each individual weather variable.