Wind vector change and fire weather index in New Zealand as a modified metric in evaluating fire danger
Siena Brody-Heine A * , Jiawei Zhang![https://orcid.org/0000-0001-7505-8870](/media/client/orcid_16x16.png)
![https://orcid.org/0000-0002-4876-2683](/media/client/orcid_16x16.png)
A University of Canterbury, School of Earth and Environment, Christchurch, New Zealand.
B Scion, New Zealand Forest Research Institute Limited, Christchurch, New Zealand.
C Fire and Emergency New Zealand, Christchurch, New Zealand.
International Journal of Wildland Fire 32(6) 872-885 https://doi.org/10.1071/WF22106
Submitted: 23 June 2022 Accepted: 16 March 2023 Published: 31 March 2023
© 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of IAWF. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)
Abstract
Background: Wildfire spread is influenced significantly by the weather variability. Wind speed and direction changes, resulting from synoptic weather systems and small-scale meteorological processes in complex terrain, can drastically alter fire intensity and spread.
Aims: To investigate the use of vector wind change (VWC) integrated with the Fire Weather Index (FWI) as a new metric in fire danger.
Methods: A 20-year FWI and modified FWI was calculated from weather station and gridded numerical weather simulation data.
Key results: High VWC is found primarily on the South Island, inland and in areas of complex terrain. After incorporating VWC into the FWI, data from the modified FWI show spatiotemporal patterns that highlight the impact of wind variability in the fire danger.
Conclusions: High VWC station data mapped with synoptic type suggest the primary factor in determining high VWC is meso- and micro-scale terrain-driven meteorology, not larger synoptic regimes.
Implications: The current fire danger metric, the Fire Weather Index (FWI), does not include wind direction changes for high wind speeds. Therefore, the inclusion of VWC as an additional metric in fire danger calculations in a modified FWI could increase operational understanding of high-danger locations and terrain impacts on extreme and unpredictable fire behaviour.
Keywords: danger, fire behaviour, fire severity, FWI, mesoscale meterology, vector wind change, weather, wildfire risk.
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