Coupling interactive fire with atmospheric composition and climate in the UK Earth System Model

João C Teixeira,Gerd A Folberth,Apostolos Voulgarakis,Fiona M O'Connor,Nadine Unger

doi:10.5194/gmd-14-6515-2021

Abstract

Abstract. Fire constitutes a key process in the Earth system (ES), being driven by climate as well as affecting the climate by changing atmospheric composition and impacting the terrestrial carbon cycle. However, studies on the effects of fires on atmospheric composition, radiative forcing and climate have been limited to date, as the current generation of ES models (ESMs) does not include fully atmosphere–composition–vegetation coupled fires feedbacks. The aim of this work is to develop and evaluate a fully coupled fire–composition–climate ES model. For this, the INteractive Fires and Emissions algoRithm for Natural envirOnments (INFERNO) fire model is coupled to the atmosphere-only configuration of the UK's Earth System Model (UKESM1). This fire–atmosphere interaction through atmospheric chemistry and aerosols allows for fire emissions to influence radiation, clouds and generally weather, which can consequently influence the meteorological drivers of fire. Additionally, INFERNO is updated based on recent developments in the literature to improve the representation of human and/or economic factors in the anthropogenic ignition and suppression of fire. This work presents an assessment of the effects of interactive fire coupling on atmospheric composition and climate compared to the standard UKESM1 configuration that uses prescribed fire emissions. Results show a similar performance when using the fire–atmosphere coupling (the “online” version of the model) when compared to the offline UKESM1 that uses prescribed fire. The model can reproduce observed present-day global fire emissions of carbon monoxide (CO) and aerosols, despite underestimating the global average burnt area. However, at a regional scale, there is an overestimation of fire emissions over Africa due to the misrepresentation of the underlying vegetation types and an underestimation over equatorial Asia due to a lack of representation of peat fires. Despite this, comparing model results with observations of CO column mixing ratio and aerosol optical depth (AOD) show that the fire–atmosphere coupled configuration has a similar performance when compared to UKESM1. In fact, including the interactive biomass burning emissions improves the interannual CO atmospheric column variability and consequently its seasonality over the main biomass burning regions – Africa and South America. Similarly, for aerosols, the AOD results broadly agree with the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Aerosol Robotic Network (AERONET) observations.

Highlights

Fires can exert a substantial forcing on the Earth’s climate by affecting different components of the Earth system (ES) such as the biosphere, atmosphere and cryosphere (Bowman et al, 2009; Daniau et al, 2013)
The root mean squared error (RMSE) is increased from 19.03 ppb in UKESM1 to 28.88 ppb in UKESM1+INFERNO. Both configurations show similar high correlations with TES-AURA (94.89 % and 94.89 % for UKESM1 and UKESM1+INFERNO, respectively). These results show that, despite the large bias caused by the vegetation errors for this region, the UKESM1+INFERNO configuration captures the observed variability of carbon monoxide (CO), representing the two peaks in CO that occur in April and August
The goal of this work was the development and evaluation of the implementation of a coupled fire–climate–composition ES model. This was built on top of the work developed by Mangeon et al (2016), coupling the INFERNO fire model to the atmosphere-only configuration of version 1 of the UK’s Earth System Model (UKESM1)

Summary

Introduction

Fires can exert a substantial forcing on the Earth’s climate by affecting different components of the Earth system (ES) such as the biosphere, atmosphere and cryosphere (Bowman et al, 2009; Daniau et al, 2013). Changes in vegetation cover caused by the fire modifies the regional to localscale surface albedo, soil water holding capacity and surface evaporation, resulting in complex interactions and feedbacks within the climate system (Li et al, 2017; Myhre, 2005). Fire emissions contribute to the global budgets of greenhouse gases (methane, ozone) and aerosol particles (black carbon, organic carbon) Teixeira et al.: Coupling interactive fire with atmospheric composition and climate in UKESM

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