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Model-based Estimation of Methane Emission from Rice Fields in Bangladesh

Md. Reaz Uddin Khan
Centre for Climate Change and Environmental Research (C3ER), BRAC University, Dhaka 1212, Bangladesh

Abul Fazal M. Saleh
Institute of Water and Flood Management (IWFM), Bangladesh University of Engineering and Technology (BUET), Dhaka 1000, Bangladesh

Abstract/ Executive Summary:

Methane, a leading heat-trapping greenhouse gas (GHG), is produced primarily as a byproduct of intensive water use in rice cultivation. Though Bangladesh is the fourth-largest rice producing country in the world, its methane emission status has yet to be determined in order to consider future mitigation measures.Hence, this study employed CH4MOD2.5, the most widely-validated computer simulated semi-empirical model and the Intergovernmental Panel on Climate Change (IPCC)proposed simulation model were used in this study for estimation of methane emissions. Three focus group discussions (FGDs)were conducted with farmers of the Gazipur District to collect information for model inputs. Using IPCC methods, the average methane emission of Bangladesh was estimated to reach1071 Gg yr^-1. The rate estimated by theCH4MOD2.5 model was464 Gg yr-1. Cultivar-specific average emissions for BR 11, BRRI dhan 28 and BRRI dhan29 were 20.4×10^-2, 69.9×10^-2 and 96.7×10^-2 kg CH4ha^-1day^-1, respectively. The projected emission values for all types of rice cultivation in Bangladesh conducted by United States Environmental Protection Agency (US-EPA)were 850 and 918 Gg in 2005 and 2010, respectively. Conversely, according to the IPCC methodology and the CH4MOD2.5 model, those figures were respectively estimated at 1087 and 1146 Gg in 2005, and at471 and 496 Gg in 2011. Among the three methods, emission estimation was highest according to the IPCC methodology and lowest according to the CH4MOD2.5 model (45% lower than the US-EPA value). The variation is primarily due to the consideration of field level data as CH4MOD 2.5 model inputs. In the business as usual scenario, Bangladesh’s predicted methane emission is approximately 653 and 906 Gg for 2030 and 2050, respectively.

Keywords: Methane Emission; CH4 MOD2.5 Model; IPCC Model; Climate Change

Location:

Start Date:

End Date:

Program Area: Socio-economic and Policy

Commodity: Rice

Objectives:

The primary goal of this study was to estimate the status of methane emissions from rice fields in Bangladesh.Additionally, the current study also attempts to predict future methane emissions from irrigated rice fields under the business as usual perspective in Bangladesh. A simulation model was used to calculate the total emissions, and results were compared with those of two methods previously applied to the same inventory.Several Participatory Rural Appraisal (PRA) tools and techniques such as FGD and KII (Key Informants Interview) were applied to collect the input values for the simulation model.

Methodology:

Following carbondioxide, methan estemmed from anthropogenic sources is the most effective GHG in the earth’s atmosphere, which contributes approximately 20% of the effects of global warming over the last century. Like other GHGs such as carbon dioxide, nitrous oxide and chlorofluorocarbons, methane has a strong infrared absorption band and traps outgoing long-wave radiation from the surface of the earth, particularly thermal radiation. Though the concentration of methane is less than that of carbon dioxide, methane is a 30 times more competent heat trapper as compared to carbon dioxide. The methane concentration in the atmosphere was estimated at 1.75 parts per million volumes (ppm V) in 2000, and due to anthropogenic activities, the emission rate is increasing at a rate of 1% per year. It is projected that the global average temperature will increase by approximately1°C and 3°C by the years 2025 and 2100, respectively. Consequently, researchers have paid increasing attention to methane emission as it plays a significant role in concurrent climate change issues. In this study, the CH4MOD2.5 estimation model was used to estimate methane emissions from rice fields in Bangladesh. Results are then compared to emission values generated by a model proposed by the IPCC in a 2006 inventory of national greenhouse gases. The two calculated values are then compared to US-EPA estimated and projected values. The CH4MOD2.5 model was also employed to estimate projections of future methane emissions from irrigated rice fields in 2030 and 2050, for the business as usual scenario. A.Calculation of Methane Emission from Rice Fields According to IPCC Methodology An estimation of the methane emissions from rice fields in Bangladesh (both Aman and Boro rice) was calculated for the decade from 2000 to 2009 by employing Eq. (1), below, as prescribed in the Guidelines for National Greenhouse Gas Inventories. IPCC prescribed the value of the harvested area Ai.j.kfor a single cropping pattern, representing the total cultivated area for that particular rice in a given year. However, in Bangladesh, the total cultivable land used for Aman rice in a given year is not identical to the total cultivable land dedicated to Boro rice. Therefore, the specific harvested areas for Aman and Boro rice were collected in a given year, and collectively considered to be the annual harvested area for that particular year.

Source of Information: Journal of Agricultural Engineering and Biotechnology Nov. 2015, Vol. 3 Iss. 4, PP. 125-137

Article Link (Online Journal): DOI: 10.18005/JAEB0304001

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

In this study, an attempt was made to identify the present status of methane emissions from Bangladesh rice fields, as it is one of the leading rice-producing countries in the world. The total harvested area in terms of Aus cultivation is not significant in Bangladesh, so Boro rice and Aman rice from specific water regimes were the only harvested areas considered in this study. BRRI dhan28 and BRRI dhan29 were selected as the Boro rice cultivars and BR 11 was been selected as the Aman rice cultivar for the estimation. The CH4MOD2.5 simulation model was employed to estimate methane emissions from rice fields in Bangladesh. IPCC-prescribed methodology was also used to compare with model results. From the year 2000 to 2009,Bangladesh rice fields emittedan average of 1071 Gg of methane inboth seasons[15]. Variety-specific annual emission rates were calculated for BR 11 (48.3×10^-2 kg CH4 ha^-1day^-1) and for BRRI dhan 28 and BRRI dhan 29 (197.5×10^-² kg CH4 ha^-1day^-1). Furthermore, due to lack of cultivar-specific scaling factors, identical emission rates were observed for BRRI dhan28 and BRRI dhan29. However, the model calculated average annual emission rates to be464 Gg, in which 83% of methane emissions came from Boro rice,and the remaining from Aman rice. The emission rate for BRRI dhan 28 (69.9×10^-2 kg CH4ha^-1day^-1) was 27% lower than that of BRRI dhan 29 (96.7×10^-2 kg CH4 ha^-1day^-1). The lowest emission rate was calculated for BR 11 (20.4×10^-2kg CH4 ha^-1day^-1). According to the IPCC method, the US-EPA tried to project the emission of methane from all sorts of rice cultivars and water regimes in developing countries, which is also taken into consider to compare the values estimated by the other two methods. The projection reported that Bangladesh emitted approximately 850 Gg and 918 Gg of methane in they ears 2005 and 2010, respectively. Conversely, this figure was estimated at 1087 Gg and 471 Gg in 2005 and 1146 Gg and 496 Gg in 2009 according to IPCC 2006 methodology and the CH4MOD2.5 simulation model, respectively. If no intervention is undertaken in the future, the country will emit approximately 653 Gg (213 Gg from BRRI dhan28 and 440 Gg from BRRI dhan29) and 906 Gg (296 Gg from BRRI dhan28 and 610 Gg from BRRI dhan29) of methane from irrigated Boro rice in the years 2030 and 2050, respectively, under the A1B emission scenario. The annual methane emission rate estimated through this study will help Bangladesh to identify its position in GHG emissions from rice cultivation in comparison to other rice-producing countries around the world. However, the on-field gas chamber primary estimation is highly recommended for Bangladesh. The result of future projections will help policy makers, researchers and relevant authorities take initiatives to investigate mitigation measures and create opportunities for carbon trade-offs.

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