Preprints
https://doi.org/10.5194/nhess-2024-161
https://doi.org/10.5194/nhess-2024-161
27 Sep 2024
 | 27 Sep 2024
Status: this preprint is currently under review for the journal NHESS.

Extreme blocking ridges are associated with large wildfires in England

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

Abstract. Persistent positive anomalies in 500 hPa geopotential heights (PPAs) are an event-based paradigm for tracking specific large scale atmospheric patterns that often correspond to blocking events. PPAs are associated with hot, dry surface weather conditions that promote fuel aridity and wildfire activity. We examine the importance of PPA events for surface fire weather across the UK and wildfires in England, a temperate, emerging fire prone region. Surface fire weather is more extreme under PPAs, characterised by reduced precipitation and anomalously high temperatures. Overall, 34 % of England’s burned area and 16 % of all wildfire events occur during or up to five days following the presence of a PPA event. PPAs are generally more strongly associated with wildfire burned area than ignition frequency. The percentage of PPAs associated with wildfire events increases with increasing fire size, with PPAs being associated with half of wildfire events > 500 ha. PPAs are most important for heathland/moorland (40 % burned area) followed by grassland (30 % burned area) wildfires and are more important during the summer wildfire season. Synoptic-scale indicators of wildfire activity like PPAs may improve longer-term fire weather forecasts beyond surface fire weather indices alone, aiding wildfire preparedness and management decision-making. This is particularly important in emerging fire prone regions where wildfire risk is increasing but established tools for assessing fire danger may not yet exist.

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

Status: open (until 08 Nov 2024)

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

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Short summary
We demonstrate the importance of Persistent Positive Anomalies in 500 hPa Geopotential Heights (PPAs) for fire weather and wildfires in a temperate, emerging fire prone region using comprehensive wildfire occurrence records. PPAs become increasingly important for larger wildfires and are most important for heathland/moorland and grassland wildfires. Our findings demonstrate the potential of synoptic indicators for extending forecasting tools to aid wildfire preparedness and management.
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