Calibration and evaluation of the Canadian Forest Fire Weather Index (FWI) System for improved wildland fire danger rating in the United Kingdom
Article, Other literature type
Jong, Mark C.
Wooster, Martin J.
McCall, Frank F.
(issn: 1684-9981, eissn: 1684-9981)
Earth and Planetary Sciences(all) | /dk/atira/pure/subjectarea/asjc/1900
Wildfires in the United Kingdom (UK) pose a threat to people, infrastructure
and the natural environment. During periods of particularly fire-prone
weather, wildfires can occur simultaneously across large areas, placing
considerable stress upon the resources of fire and rescue
services. Fire danger rating
systems (FDRSs) attempt to anticipate periods of heightened fire risk,
primarily for early-warning and preparedness purposes. The UK FDRS, termed
the Met Office Fire Severity Index (MOFSI), is based on the Fire Weather
Index (FWI) component of the Canadian Forest FWI System. The MOFSI currently
provides daily operational mapping of landscape fire danger across England
and Wales using a simple thresholding of the final FWI component of the
Canadian FWI System. However, it is known that the system has scope for
improvement. Here we explore a climatology of the six FWI System components
across the UK (i.e. extending to Scotland and Northern Ireland), calculated
from daily 2<mspace width="0.125em" linebreak="nobreak"/>km × 2<mspace linebreak="nobreak" width="0.125em"/>km gridded numerical weather
prediction data and supplemented by long-term meteorological station
observations. We used this climatology to develop a percentile-based
calibration of the FWI System, optimised for UK conditions. We find this
approach to be well justified, as the values of the "raw" uncalibrated FWI
components corresponding to a very "extreme" (99th percentile) fire danger
situation vary by more than an order of magnitude across the country.
Therefore, a simple thresholding of the uncalibrated component values (as is
currently applied in the MOFSI) may incur large errors of omission and
commission with respect to the identification of periods of significantly
elevated fire danger. We evaluate our approach to enhancing UK fire danger
rating using records of wildfire occurrence and find that the Fine Fuel
Moisture Code (FFMC), Initial Spread Index (ISI) and FWI
components of the FWI System generally have the greatest
predictive skill for landscape fire activity across Great Britain, with
performance varying seasonally and by land cover type. At the height of the
most recent severe wildfire period in the UK (2 May 2011), 50 % of all
wildfires occurred in areas where the FWI component exceeded the 99th
percentile. When all wildfire events during the 2010–2012 period are
considered, the 75th, 90th and 99th percentiles of at least one FWI component
were exceeded during 85, 61 and 18 % of all wildfires respectively.
Overall, we demonstrate the significant advantages of using a
percentile-based calibration approach for classifying UK fire danger, and
believe that our findings provide useful insights for future development of
the current operational MOFSI UK FDRS.