The objective of this project was to develop high-resolution, spatially explicit data layers describing wildfire hazard across New Zealand. These layers include both fuel moisture codes and fire behaviour indices of the Fire Weather Index (FWI) System (Van Wagner & Pickett 1985), which is widely used by Rural Fire Authorities to provide an indication of climatic conditions leading to high fire danger, and derived layers describing fire behaviour. The resulting digital maps will be key inputs to the subsequent prediction of spatial variation of fire hazard by Rural Fire Authorities, performed as part of a Wildfire Threat Analysis Project.

Weather data measured over time across the NRFA weather station network were used to calculate average fire hazard during the worst 20% of days in the fire season. Mathematical surfaces were fitted to these data to enable estimation of standard fire weather indices (FWI) across New Zealand. The resulting grid data layers (rasters) describing FWI indices were combined with data describing fuel loads and slope to derive additional data layers describing rate of fire spread and head fire intensity.

Results indicate considerable spatial variation in fire threat, with highest threats occurring in warm, dry climates. Data manipulation posed challenges, given the size of the datasets involved and the need to convert complex mathematical equations into object-oriented expressions.

Production of spatial data layers describing spatial variation in fire threat will facilitate the incorporation of more detailed information about spatial variation in fuel loads by rural fire authorities.