Extreme blocking ridges are associated with vegetation fire occurrence in England
Kerryn Little
A * , Dante Castellanos-Acuna B , Nicholas Kettridge A , Mike Flannigan B and Piyush Jain C
A
B
C
Abstract
Persistent positive anomalies (PPAs) in 500 hPa geopotential heights are an event-based paradigm for tracking large scale atmospheric patterns that often correspond to blocking events.
Examine the importance of PPAs for surface fire weather across the United Kingdom (UK) and vegetation fire occurrence in England.
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.
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 5 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.
PPAs are associated with elevated surface fire weather and vegetation fires. They are especially important for larger fires in heathland/moorland and grasslands.
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.
Keywords: atmospheric circulation, burned area, fire weather, high pressure, PPA, synoptic, UK, wildfire.
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