Spatio-temporal patters of fire in humid-Atlantic Europe: is vegetation phenology rather than fire weather the key driver? 

Abstract

Fire weather indices are used widely as predictors for landscape fire potential. However, for the United Kingdom (UK: England, N-Ireland, Scotland and Wales) and comparable regions of humid-Atlantic Europe, they do not correlate well with fire occurrence. Here we explore the role of vegetation phenology as a key driver for fire occurrence in the UK. We mapped satellite-derived fire occurrence and phenology climatology for 2012-2023 onto main fire-affected vegetation cover types within distinct precipitation regions for the UK. This enabled fire occurrence for fuels in different phenological phases to be explored across distinct ‘fuel’ types and regions. Semi-natural grassland and dwarf shrub-dominated land emerged as the prominent fire affected ecosystems across much of the UK. We found that, critically, fire occurrence for vegetation at its maximum greenness were reduced by a factor of five to six compared to dormant vegetation, despite higher fire weather indices being typically associated with the former. In contrast to most regions of the world that exhibit more extreme fire weather, fire activity in the UK’s humid Atlantic climate therefore seems strongly governed by vegetation phenology. This suggests that incorporating vegetation phenology is la critical step in the development of robust fire risk and behaviour prediction systems for regions with similar climate. It should be noted, however, that we also found evidence of that this fire-suppressing phenology barrier can be broken during extreme summer heat/drought events, which are likely to increase in frequency and severity under changing climate.  Hence fire weather indices remain critical predictors during the currently still rare extreme summer heat/drought events.