Calibration and evaluation of the Canadian Forest Fire Weather Index (FWI) System for improved wildland fire danger rating in the United Kingdom

Abstract

Abstract. 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 earlywarning 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 km × 2 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.

Drought-Forest Fire Relationships

“…Canadian FWI system is one of the most commonly used fire weather indices all over the world thanks to its success in determining the fire risk and flexibility although it was originally developed for Canada [38][39][40]. Beside this, six components forming the system can individually estimate the fire risk in a succesful way in different conditions.…”

“…It was stated by Viegas et al [10] in France that ISI (Initial Spread Index), as a FWI component, is successful under extreme fire conditions. Jong et al [11] state that the 75, 90 and 99% uses of at least one of the FWI components for the UK is of a significant advantage in calibration studies. Bedia et al [12] emphasized DSR (Daily Severity Ratio) and FWIP90 as FWI components for a better understanding of the spatial and temporal distribution of fires in Spain and identified an increase in the amount of burned areas.…”

Development of a national index for the purpose of forest fire risk assessments on the example of southern Serbia

“…Since the data of daily measurements are presented in the Meteorological Yearbook of the Republic Hydrometeorological Service of Serbia, the issue of the possible use of the Canadian Forest FWI has become increasingly pronounced. Its application is hindered by distinct orographic characteristics of the area of Serbia which require very extensive research in order to develop correction parameters [12] and a different risk scale. Therefore, we have developed a modified Angstrom index which provides a simpler way of determining the degree of forest fire vulnerability [13].…”

Regional variation in fire weather controls the reported occurrence of Scottish wildfires

“…A critical part of any response system for managing wildfire is the need to be able to plan for periods of significant wildfire activity and safely complete managed burning activities. Substantial research has therefore been focused on the assessment of global (e.g., Scholze et al, 2006), national (e.g., Tanskanen & Venäläinen, 2008; de Jong et al, 2016) and regional (e.g., Dimitrakopoulos, Bemmerzouk & Mitsopoulos, 2011; Beccari et al, 2015) assessments of climatic drivers of wildfire activity. Modeling wildfire activity remains challenging both due to the quality of historical fire data available from documentary records and satellite data (Murphy et al, 2000; Krawchuk & Moritz, 2014), and the statistical challenges involved (e.g., Andrews, Loftsgaarden & Bradshaw, 2003; Eastaugh, Arpaci & Vacik, 2012; de Jong et al, 2016).…”

“…A limited system currently exists in the form of the Met Office Fire Severity Index (MOFSI; Kitchen et al, 2006) developed for England and Wales in response to the CROW Act. MOFSI is based on the FWI system which recent research suggests has promise for detecting variation in fire risk across the UK despite important regional variation in temporal patterns in FWI system codes/indices (de Jong et al, 2016). MOFSI’s single five-point index is not sufficient to capture variation in weather and fuel conditions that are of interest to those who work with vegetation fires in the UK or who are responsible for responding to wildfire events.…”