Heatwaves and firewaves: the drivers of urban wildfires in London in the summer of 2022

Abstract In the summer of 2022, a series of heatwaves caused an unprecedented wave of wildfires across the UK. London, in particular, was badly affected. Its green spaces wilted, and the drying vegetation provided the fuel for wildfires. The London Fire Brigade (LFB), one of the largest firefighting organisations in the world, was overwhelmed. On 19th July 2022, it experienced its busiest day since World War II. Our work represents a first attempt to examine and quantify the link between heatwaves and wildfires in a city. We combine fire incident data from the LFB and meteorological data from the Met Office, from 2009–2022, identifying vapour pressure deficit (VPD) as a key driver of wildfires in the urban habitants of Greater London. Wildfire activity is characterised using the number of recorded wildfires, and the time spent at incidents by the LFB’s fire pumps. We find that VPD is able to explain up to 61% of the variation in number of London wildfires. Relative humidity, and maximum daily temperature are only able to explain 44% and 42% of the variation respectively. We find that the Met Office’s definition of a heatwave – defined for the purpose of public health – is unsuited to describe the process of vegetation drying, and propose a new definition using data from the Met Office, based on vapour pressure deficit. Further, using the time spent at incidents by the LFB’s pumps, we define and identify the concept of a ‘firewave’ for London, in order to quantify the severity of a day of wildfires for the LFB. It is hoped that the results will be of operational value to the LFB, and lay the foundation for further work investigating the role of heatwaves and VPD in increasing wildfire risk in cities and other urban environments.