Wildfire threat analysis in the forest-urban interface – a scoping study for the Swinley forest area

Manchester University and Forestry Commission England undertook a 6-month, NERC-funded scoping study of Wildfire Threat Analysis (WTA) for the UK. WTA was developed in Canada and applied nationally in New Zealand. Threat is seen as a combination of three GIS modules: Risk of Ignition (RoI) of vegetation fires; Hazard of fire spread (head fire intensity, rate of spread); and Values at Risk (VaR, assets potentially affected). RoI and VaR modules were successfully developed for a 11x12 km forest-urban interface area centred on Crowthorne Wood/Swinley Forest, where a severe wildfire occurred in April-May 2011. Guided by expert knowledge from two stakeholder workshops, we adapted New Zealand’s map layers (causal factors) to produce a data catalogue of > 90 mostly publically-available, map layers. Layers were ‘scored’ using stakeholder knowledge and geo-locations of Incident Recording System (IRS) vegetation fires; e.g. each land cover type was given a relative risk of ignition score (as a proxy for fuel and land use). The Hazard module was limited by the (then) lack of fire climate data. Using expert opinion, weighted combinations of layers yielded 25m cell size RoI map and three VaR maps; social vulnerability, infrastructure and ecosystem services. Taken together, hotspots requiring management were identified.