Methane emissions from rice cultivation in West Africa and compensation options from nature reserve forests.
Rice cultivation is hugely important for global food security. By expanding regional rice cultivation, West Africa aims to become less dependent on rice imports. Due to the associated emissions of the greenhouse gas methane, compensation options are being sought, such as natural forest reserves as natural methane sinks. In the study presented here, Samuel Guug and colleagues investigated for the first time the dynamic interaction between methane emissions from rain-fed rice cultivation and their potential reduction through methane uptake in the forests of the semi-arid savannah region of West Africa. What makes the study unique is that the methane emissions were quantified using the technically complex eddy covariance method. In West Africa, where data is scarce, this is one of the first direct measurements of methane emissions.
The key findings of the study:
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The rice fields studied were a net source of methane at a rate of 2.04 g methane per m2.
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This corresponds to a global warming potential of 171 g CO2eq over a period of 20 years.
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70% of methane emissions were generated during the main growth phase of the rice in August.
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The savannah forest in the nature reserve acted as a methane sink (-0.56 g methane per m2) during the rainy season, with a negative global warming potential of -47 g CO2eq.
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Approximately four times more forest area is needed to offset methane emissions from rice cultivation.
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Site conditions such as soil moisture and ground heat significantly influence the net balance between methane uptake and production.
Contacts:
Reconciling climate protection and food security
Due to rapid population growth and national initiatives to reduce dependence on rice imports, rice cultivation is being intensified in West Africa. However, rice cultivation causes methane emissions into the atmosphere. Methane is an important and powerful greenhouse gas, and its emissions from agricultural activities, particularly rice cultivation, are a significant challenge for mitigating climate change. Methane measurements for this study were taken during the 2023 rainy season at two sites with different land uses, one in rice fields in Janga and the other in a protected forest reserve in Mole National Park. Both sites are located in the savannah region of West Africa in northern Ghana. The average emissions from the rice fields were just over two grams per square metre. With a cultivation area of one square kilometre, this means that more than two tonnes of methane are released into the atmosphere through rice cultivation.
In contrast, the savannah forest in Mole National Park acted as a methane sink. At this location, 0.56 grams of methane per square metre were stored from the land surface. This means that approximately four times more forest area is needed to offset methane emissions from rice cultivation.
Citation:
Guug, S.; Sy, S.; Quansah, E.; Bliefernicht, J.; Neidl, F.; Steinbrecher, R.; Ayamba, M.; Frempong, A.; Davies, P.; Spangenberg, I.; et al. Methane emissions from rice cultivation in West Africa and compensation options from nature reserve forests. Environmental Research Letters 2025, 20 (4), 044050. DOI: 10.1088/1748-9326/adc28c.
Harnessing local potential for greenhouse gas reduction
This study highlights the need to protect savannah forests in West Africa and integrate them into climate protection measures in order to offset the methane released by rice cultivation. Forests can serve as greenhouse gas sinks and should be included in mitigation strategies alongside direct reductions in greenhouse gas emissions. When considering and balancing greenhouse gas emissions, the regional context and local potential for carbon reduction are important. West Africa relies heavily on rain-fed rice cultivation, which has so far had to manage without artificial irrigation.
Therefore, the findings on the conditions under which a forest can absorb and break down particularly large amounts of methane are of great interest for climate protection. The ability of forests to serve as methane sinks also depends heavily on local conditions and the protection of the forest and its ecosystem functions.
Related Articles:
Bliefernicht, J.; Berger, S.; Salack, S.; Guug, S.; Hingerl, L.; Heinzeller, D.; Mauder, M.; Steinbrecher, R.; Steup, G.; Bossa, A. Y.; et al. The WASCAL Hydrometeorological Observatory in the Sudan Savanna of Burkina Faso and Ghana. Vadose Zone Journal 2018, 17 (1), 180065.
Worth knowing
Methane (CH₄) is a much more powerful greenhouse gas than carbon dioxide (CO₂) because it traps more heat from solar radiation in the atmosphere. Over a period of 100 years, methane has a warming effect that is approximately 28 times greater than that of CO₂, and over a period of 20 years, the effect is even 86 times greater. This is due to several factors:
- Heat storage efficiency: Methane absorbs infrared radiation more effectively than CO₂, which means it retains heat more effectively
- Short lifespan: Methane only remains in the atmosphere for around 12 years, while CO₂ can survive for centuries. This means that methane has a much greater impact on global warming in the short term.
- Natural and anthropogenic sources: Methane is released through biological processes in agriculture, such as the digestion of ruminants and rice cultivation. Methane is also frequently released during the extraction of fossil fuels. Man-made global warming is also leading to increased methane emissions from thawing permafrost soils.
