Rain-fed pulses of methane from East Africa during 2018–2019 contributed to atmospheric growth rate

Mark F Lunt,Tobias Borsdorff,Hartmut Boesch,Robert J Parker,Alba Lorente,Paul I Palmer,Jochen Landgraf

doi:10.1088/1748-9326/abd8fa

Abstract

East Africa is a key location for wetland emissions of methane (CH4), driven by variations in rainfall that are in turn influenced by sea-surface temperature gradients over the Indian Ocean. Using satellite observations of CH4 and an atmospheric chemistry-transport model, we quantified East African CH4 emissions during 2018 and 2019 when there was 3-σ anomalous rainfall during the long rains (March–May) in 2018 and the short rains (October–December) in 2019. These rainfall anomalies resulted in CH4 emissions of 6.2 ± 0.3 Tg CH4 and 8.6 ± 0.3 Tg CH4, in each three month period, respectively, and represent a 10% and 37% increase compared to the equivalent season in the opposite year, when rainfall was close to the long-term seasonal mean. We find the additional short rains emissions were equivalent to over a quarter of the growth in global emissions in 2019, highlighting the disproportionate role of East Africa in the global CH4 budget.

Highlights

Introduction ceAc ptThe atmospheric concentration of methane (CH4 ), an important greenhouse gas, has continued to rise through the 20th century with only a brief respite early this century between 2000 and 2007
Two CH4 satellite datasets are used in this study to examine changes over East Africa: TROPOMI and GOSAT
We find that the largest component of the seasonal OND emissions peak in both years is from wetlands emissions (60%) followed by agriculture (15%), based on the difference between a posteriori emissions in OND and June

Summary

Introduction ce

The atmospheric concentration of methane (CH4 ), an important greenhouse gas, has continued to rise through the 20th century with only a brief respite early this century between 2000 and 2007. The wet seasons in East Africa follow the movement of the inter-tropical convergence zone. Northern regions such as Sudan and northern Ethiopia have one wet season which normally peaks in July–September. March–May (MAM) and October–December (OND) (Herrmann & Mohr 2011) These two wet seasons are termed the long rains and short rains, respectively, and are the focus of this paper. OND that were one of the wettest short rains seasons on record (Wainwright et al 2020) This followed anomalously high precipitation levels during the MAM 2018 long rains (Kilavi et al 2018). We use satellite observations of CH4 from two independent instruments to investigate the impact of these precipitation anomalies on CH4 emissions from East Africa

Satellite data us cri an pte

GEOS-Chem Chemistry Transport model

Emissions estimation

Results

Data availability an