Estimation of fire-induced carbon emissions from Equatorial Asia in 2015 using in situ aircraft and ship observations

Yosuke Niwa,Hideki Nara,Yousuke Sawa,Shin-Ichiro Nakaoka,Toshinobu Machida,Yasunori Tohjima,Akihiko Ito,Hidekazu Matsueda,Hiroshi Tanimoto,Taku Umezawa

doi:10.5194/acp-21-9455-2021

Yosuke Niwa, Hideki Nara + Show 8 more

Open Access

https://doi.org/10.5194/acp-21-9455-2021

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Abstract

Abstract. Inverse analysis was used to estimate fire carbon emissions in Equatorial Asia induced by the big El Niño event in 2015. This inverse analysis is unique because it extensively used high-precision atmospheric mole fraction data of carbon dioxide (CO2) from the commercial aircraft observation project CONTRAIL. Through comparisons with independent shipboard observations, especially carbon monoxide (CO) data, the validity of the estimated fire-induced carbon emissions was demonstrated. The best estimate, which used both aircraft and shipboard CO2 observations, indicated 273 Tg C for fire emissions from September–October 2015. This 2-month period accounts for 75 % of the annual total fire emissions and 45 % of the annual total net carbon flux within the region, indicating that fire emissions are a dominant driving force of interannual variations of carbon fluxes in Equatorial Asia. Several sensitivity experiments demonstrated that aircraft observations could measure fire signals, though they showed a certain degree of sensitivity to prior fire-emission data. The inversions coherently estimated smaller fire emissions than the prior data, partially because of the small contribution of peatland fires indicated by enhancement ratios of CO and CO2 observed by the ship. In future warmer climate conditions, Equatorial Asia may experience more severe droughts, which risks releasing a large amount of carbon into the atmosphere. Therefore, the continuation of aircraft and shipboard observations is fruitful for reliable monitoring of carbon fluxes in Equatorial Asia.

Highlights

Equatorial Asia, which includes Indonesia, Malaysia, Papua New Guinea and the surrounding areas (Fig. 1) has experienced extensive biomass burning, especially during drought conditions induced by El Niño and the Indian Ocean dipole (Field et al, 2009)
The prior model estimate showed smaller fire contributions in October than in September (Fig. 4b), the simulated total CO2 mole fractions were comparable to the observations (Fig. 3b), indicating that non-fire emissions had a certain level of contribution during this period
The estimated total net carbon flux amounts to 322 Tg C for September–October (CV_GG), 85 % of which is contributed by fire emissions (Table 3), indicating that flux variations of terrestrial photosynthesis and respiration under severe drought were not as large as those of the biomass burning emissions in 2015

Summary

Introduction

Equatorial Asia, which includes Indonesia, Malaysia, Papua New Guinea and the surrounding areas (Fig. 1) has experienced extensive biomass burning, especially during drought conditions induced by El Niño and the Indian Ocean dipole (Field et al, 2009). This biomass burning has emitted a significant amount of carbon, mainly in the form of carbon dioxide (CO2), into the atmosphere (Page et al, 2002; Patra et al, 2005; van der Werf et al, 2008). This was one of biggest El Niño events in the last 30 years, rivalling the well-known major El Niño in 1997/1998 (L’Heureux et al, 2017; Santoso et al, 2017). Page et al (2002) estimated that the biomass burning in 1997 emitted a massive amount of carbon into the atmosphere, ranging between 810 and 2570 Tg C

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