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

Abstract

Abstract. Wildfires in the United Kingdom (UK) can pose a threat to people, infrastructure and the natural environment (e.g. to the carbon in peat soils), and their simultaneous occurrence within and across UK regions can periodically place considerable stress upon the resources of Fire and Rescue Services. "Fire danger" rating systems (FDRS) attempt to anticipate periods of heightened fire risk, primarily for early-warning 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. MOFSI currently provides operational mapping of landscape fire danger across England and Wales using a simple thresholding of the final FWI component of the Canadian System. Here we explore a climatology of the full set of FWI System components across the entire UK (i.e. extending to Scotland and Northern Ireland), calculated from daily 2 km gridded numerical weather prediction data, supplemented by meteorological station observations. We used this to develop a percentile-based calibration of the FWI System optimised for UK conditions. We find the calibration to be well justified, since for example the values of the "raw" uncalibrated FWI components corresponding to a very "extreme" (99th percentile) fire danger situation can vary by up to an order of magnitude across UK regions. Therefore, simple thresholding of the uncalibrated component values (as is currently applied) may be prone to large errors of omission and commission with respect to identifying periods of significantly elevated fire danger compared to "routine" variability. We evaluate our calibrated approach to UK fire danger rating against records of wildfire occurrence, and find that the Fine Fuel Moisture Code (FFMC), Initial Spread Index (ISI) and final FWI component of the FWI system generally have the greatest predictive skill for landscape fires in 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, and for each of the ten most serious wildfire events that occurred in the 2010–2012 period, at least one FWI component per event was found to surpass the 95th percentile. Overall, we demonstrate the significant advantages of using a calibrated, percentile-based approach for classifying UK fire danger, and believe our findings provide useful insights for any future redevelopment of the current operational UK FDRS.

Living on a flammable planet: interdisciplinary, cross-scalar and varied cultural lessons, prospects and challenges

“…These areas include Northwest Europe, especially the UK, The Netherlands and Germany, and to some extent, the eastern USA and countries such as Sweden, Japan, South Korea and New Zealand. Wildfires occur annually in these areas, but destructive fires are episodic and concentrated during hot, dry and windy weather conditions [83]. This presents the challenge that political awareness is equally sporadic, falling during wet years, whereas fuel loads accumulate and the potential for intense fires increases [84]-a temporal disconnect still largely unrecognized by policy-makers in Northwest Europe.…”

Exploring Forest Fire Dynamics: Fire Danger Mapping in Antalya Region, Türkiye

“…The DMC assesses moisture content in decomposing organic materials located 5-10 cm beneath the layer of organic surface residues and debris, playing a crucial role in evaluating moisture conditions within this specific layer of organic material. DC measures the organic moisture content at a depth of 10-20 cm in the forest floor [38,71]. These three subcomponents collectively describe fuel conditions, ranging The FWI system consists of six distinct subcomponents, with three of them (FFMC, DMC, and DC) specifically associated with fuel moisture codes, while the remaining three (ISI, BUI, and the general index FWI) function as fire behavior indexes [56].…”

“…The DMC assesses moisture content in decomposing organic materials located 5-10 cm beneath the layer of organic surface residues and debris, playing a crucial role in evaluating moisture conditions within this specific layer of organic material. DC measures the organic moisture content at a depth of 10-20 cm in the forest floor [38,71]. These three subcomponents collectively describe fuel conditions, ranging from the surface to deeper soil layers, encompassing litter and organic layers [2].…”

“…Some research studies noted that the combination of FFMCs with a high ISI was more effective in predicting fire occurrences for specific fuel sources compared to the overall FWI [26,72,73]. Since fuel moisture codes integrate the previous day's values, initial values need to be determined; these specific values-85 for FFMC, 6 for DMC and 15 for DC-are documented in the literature [71,74]. It is noted that these calculations may vary under different conditions.…”

Wildfire policy and management in England: an evolving response from Fire and Rescue Services, forestry and cross-sector groups

“…Vegetation fires in the UK are most prevalent in spring, when there are dry fine fuels from dead vegetation after winter freezing and drying, and during hot summers [ 23 , 24 ]. Although wildfires occur annually, the most serious incidents are intermittent, being concentrated in just a few dry years, 1976, 2003, 2006 and 2011, for example [ 25 ].…”