Metrics to indicate wildfire likelihood and severity are common worldwide; however, a growing body of research suggests that more nuanced approaches may be necessary.

The Canadian Forest Fire Weather Index launched by the Canadian Forest Service in the 1960s is now adapted for use in numerous regions, including parts of Australia, Europe and Asia. The United Kingdom also uses the index, but does not have a fire danger rating system akin to other nations.

Most decision support systems based on fire weather–fire relationships have primarily been developed in fire-prone regions that have a long history of experiencing large and extreme wildfires (Canada, Southern Europe, Australia, United States) and then adapted for use in emerging fire-prone regions that have smaller fires, many of which are not detected by satellite.

The Canada Index’s essential metrics, including humidity, temperature, precipitation, and wind speed, may not be good enough alone to predict fire occurrence in places such as the UK, according to a recently published paper. The study explored using another metric, specifically extreme atmospheric blocking events, alongside the index’s other measurements, that may better help forecast wildfires throughout the UK.

Atmospheric blocking occurs when a high-pressure system remains nearly stationary and effectively blocks airflow, causing dry conditions and high surface temperatures that promote vegetation fires, according to the paper. Tracking persistent positive anomalies, or PPAs, of the blocking events may act as a better warning system than relying on the usual fire weather indicators.

“Because of their long-development phase and slow-moving nature, (PPAs) tend to be more predictable in the medium-range of up to two weeks, compared to surface fire weather indicators that are more locally variable and get challenging to forecast beyond the short-term,” lead author and University of Birmingham researcher Kerryn Little told WildfireToday. “Considering synoptic indicators of fire weather like PPAs in addition to surface fire weather indicators may help us to get an early warning of elevated fire weather conditions to aid fire preparedness and management decision-making.”

Using PPA events and other similar indicators of fire danger periods would provide significant benefits for fire preparedness regions like the UK, which have had to rely on general fire danger assessments, rather than region-specific, tailored forecasts.

“Our research does show (like others have) that certain fire weather indicators don’t perform well where there is a strong phenological control on when fires occur. Many of our fires in the UK (and in other temperate regions of Europe) occur during spring. High temperatures and long dry periods are not necessarily needed for these fires, as live fuel moisture can be very low prior to new vegetation growth and so those indicators based on weather variables alone don’t capture this risk. To capture the spring fire season, other indicators that incorporate this phenological control are needed.”

Read the full paper Extreme blocking ridges are associated with vegetation fire occurrence in England in the International Journal of Wildland Fire. In assessing the Canadian FWI for UK use, lead author Kerryn Little and University of Birmingham colleague Nicholas Kettridge, were assisted by contributing Canadian writers Dante Castellanos-Asuna and Mike Flannigan from Thompson Rivers University, and Piyush Jain from Canada Forest Service.