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Extreme blocking ridges are associated with vegetation fire occurrence in England

Kerryn Little , Dante Castellanos-Acuna, Nicholas Kettridge , Mike Flannigan , Piyush Jain

Abstract

Background: Persistent positive anomalies in 500 hPa geopotential heights (PPAs) are an event-based paradigm for tracking large scale atmospheric patterns that often correspond to blocking events. Aims: Examine the importance of PPAs for surface fire weather across the UK and vegetation fire occurrence in England. Methods: We used linear regression models and lead-lag statistics to analyse relationships between PPAs and gridded surface weather, and we quantified landcover and season-dependent relationships between PPAs and vegetation fire occurrence and size using a comprehensive fire occurrence database. Key results: Surface fire weather is more extreme under PPAs, characterised by reduced precipitation and anomalously high temperatures. Overall, 34% of England’s burned area occurs during or up to five days following the presence of a PPA. The percentage of PPAs associated with vegetation fires increases with increasing fire size, with PPAs being associated with half of fire occurrences > 500 ha. Conclusions: PPAs are associated with elevated surface fire weather and vegetation fires. They are especially important for larger fires in heathland/moorland and grasslands. Implications: Synoptic-scale indicators of fire occurrence like PPAs may improve longer-term fire weather forecasts beyond surface fire weather indices alone, aiding vegetation fire preparedness and management decision-making.

WF25083  Accepted 18 June 2025

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