The Sensitivity of High Latitude Wildfires and their impacts on Atmospheric Composition to underlying driving processes in the UK’s Earth System Model (UKESM)

Wildfires have a significant influence on the Earth system through perturbing the carbon cycle and also emitting large quantities of short lived climate forcers (SLCFs) such as aerosol precursors (black and organic carbon) and gases that can lead to ozone formation (carbon monoxide, nitrogen oxides). SLCFs are important as they affect the Earth’s radiative balance, influencing climate, and also can have important impacts on air quality in the near-surface atmosphere. Climate change and human interference also have important effects on the size, magnitude and duration of wildfires, which are important to understand further, particularly in the context of a changing climate. Such influences are potentially important in the northern high latitudes, where wildfires have been increasing in magnitude and frequency over the last few decades. Here, we present an evaluation of the representation of high latitude wildfires in a configuration of UKESM with an interactive fire module (INFERNO) coupled to chemistry, aerosol and radiation schemes.  We also show results from sensitivity studies analysing the influence of model process drivers on high latitude wildfires and their impacts on atmospheric composition over the recent past, including from changes in climate, socio-economic factors and underlying vegetation properties.

The baseline configuration of UKESM coupled with INFERNO shows an underestimation of burnt area from high latitude wildfires over the period 2000 to 2015 compared to that reported by GFED4s. The sensitivity scenarios show that this underestimation is found to be strongly driven by the human suppression factor included within INFERNO. The underestimation in burnt area is also reflected in the emission of SLCFs from high latitude wildfires e.g. CO, with implications for both climate and air quality. The INFERNO fire scheme does not currently include the representation of peat fires, which are important sources in the high latitude. When we include a representation of SLCF emissions from high latitude peat fires, the magnitude and temporal variability of such emissions are much improved in the model and compare better with those in GFED4s. Including this additional source also increases the contribution of wildfires to particulate air pollution and the degradation in surface air quality simulated by the model over the northern high latitudes. The interactive fire model coupled within UKESM is shown to underestimate high latitude wildfires due to missing sources and the representation of human interactions in this region. This has important consequences for regional air quality and climate in an area of the world experiencing rapid changes to its climate.