A Comparison of Fire Service IRS and MODIS-Detected Vegetation Fires in Scotland

Incident Recording System (IRS) data for Scotland over four financial years, 2009/10–2012/13, show that 80% of ‘IRS-based wildfires’ (vegetation fires meeting 2013 Scottish Wildfire Operational Guidance IRS-based criteria) occurred in spring. Similarly, 92% of vegetation fire hotspots detected by MODIS thermal sensors on Terra and Aqua satellites also occurred in spring (data from NASA’s FIRMS Web Fire Mapper). Both occurred mainly in the Highlands and Islands. Attempts to match these datasets revealed that MODIS detected only 1 in 10 (53) of IRS-based wildfires because of cloud cover, timing of satellite overpasses, fire size and intensity. Approximately 47% (206) of MODIS vegetation hotspots had near-matches to IRS-based wildfires. The mismatch occurs partly because MODIS detects active fire fronts, with >1 detection for large or long-lasting fires, whereas IRS records the ignition or fire service rendezvous point, sometimes several kilometres away. Matching would be easier if IRS recorded fire perimeters, especially since cloud means that very few MODIS Burned Area perimeters are available. The remaining 53% of MODIS hotspots may not be real fires (although those on non-vegetated land cover were excluded), or were real, unreported fires. Both datasets therefore have different benefits and limitations as tools for monitoring wildfires in Scotland.