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Appendix II: Default Values for Calculating Methane Emissions from Rice

Find the rice area harvested from the FAO database for each country you selected. The values in the table give the percent of the area harvested that Irrigated (flooded 100% of the time), Rainfed (intermittently flooded) and upland rice which is not flooded and produces no methane.

The IPCC methodology was developed according to the concept that ideal conditions for methane emission from rice cultivation are those in which flooding is continuous throughout the growing season for the rice. Such continuous flooding is considered to occur only under artificially irrigated conditions. Rainfed rice cultivation is prevalent is some countries but under these conditions, fields typically are subject to intermittent flooding during the growing season. Dryland rice produces no methane. Based on measurements of methane emission from rice fields, the IPCC methodology assumes that methane emission from rice under ideal conditions (continuous flooding under irrigation) is 20 grams of methane per square meter per year (g CH4/m2/yr) and that fields managed under other water regimes (rainfed) produce methane at lower rates. In the calculation, emission factors are associated with water regimes and define the value used to "adjust" the maximum emission value of 20 g CH4/m2/yr. The emission factor for irrigated fields is 1.0 × 20 g CH4/m2/yr. For rainfed rice fields the factor is 0.8 × 20 g CH4/m2/yr if under continuous flooding, 0.4 if under intermittent flooding, and 0.6 if the flooding regime is not specified (undifferentiated).

To calculate the total methane emissions from an area, methane emissions produced under each water regime are calculated and totaled. This total is multiplied by 1×105 to convert from 107 g to 1012 g (teragrams).

Methane Calculation
Methane Total = Methane from Irrigated Fields + Methane from Undifferentiated Rainfed Fields + Methane from Rainfed fields under Continuous Flooding + Methane from Rainfed fields under Intermittent Flooding  
  = (area total × % area irrigated × factor × 20 g CH4/m2) + (area total × % area undifferentiated rainfed × factor × 20 g CH4/m2) + (area total × % area under continuous flooding × factor × 20 g CH4/m2) + (area total × % area under intermittent flooding × factor × 20 g CH4/m2) × 1×105 (to convert to Teragrams)

Example:

Country Area (107 m2) % Dry % Irrigated % Rainfed
North Korea 1200 13% 67% 20%

 

Methane emissions from continuously flooded fields
Methane emissions from continuously flooded fields = Total Area × % Irrigated × Methane Emission Factor × 20 g CH4/m2  
  = 1200 × .67 × 1 × 20 g CH4/m2 × 1×105 = 0.16 Tg

 

Methane emissions from undifferentiated rainfed fields
Methane emissions from undifferentiated rainfed fields = Total Area × % Irrigated × Methane Emission Factor × 20 g CH4/m2  
  = 1200 × .20 × 0.6 × 20 g CH4/m2 x 1×105 = 0.03 Tg

 

Total Methane
Total Methane = Emissions from Continuously Flooded Fields + Emissions from Undifferentiated Rainfed Fields    
  = 0.16 Tg + 0.03 Tg = 0.19 Tg

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