# How much methane does alternate wetting and drying cut in rice, and how do I show it to a buyer?

Canonical: https://senseible.earth/answers/awd-rice-methane-reduction-calculation

Under IPCC 2019 Refinement defaults, fields drained several times in a season emit 55% of the methane of continuously flooded fields, a 45% cut. A single drainage gives a 29% cut. Multiply your baseline methane per hectare by that cut and by verified AWD hectares, subtract any nitrous oxide increase, and back it with field water records.

## The scaling factors

Table 5.12 of the IPCC 2019 Refinement, Volume 4, Chapter 5, scales the continuously flooded methane rate by 1.00 for continuous flooding, 0.71 for a single drainage period and 0.55 for multiple drainage periods. Alternate wetting and drying, done properly, is the multiple drainage case. A field that is drained once at mid-season is the single drainage case, not AWD.

## The formula

1. Baseline methane per hectare = daily rate under continuous flooding x days of cultivation, using a regional IPCC default or measured data.
2. AWD methane = baseline x 0.55.
3. Reduction per hectare = baseline x 0.45, converted with a named GWP.
4. Subtract the extra nitrous oxide: drained soils emit more N2O, and the 2019 Refinement (Volume 4, Chapter 11) uses a direct N2O factor of 0.005 kg N2O-N per kg N for rice with single or multiple drainage against 0.003 for continuous flooding.
5. Multiply by hectares where AWD was actually practised, not hectares enrolled.

## Evidence a buyer can rely on

- Field water tube readings with dates, showing water falling below the soil surface and re-flooding, for a sample of plots each season.
- Drainage and irrigation logs by plot, and photos with location and date.
- Farmer lists with plot areas and crop calendars.
- Who checked the records, and how many plots were visited.

## How the buyer can use it

A buyer can count the lower methane in its Scope 3 Category 1 for the rice it bought from those fields, if the reduction is traced to its supply. If the same reduction is sold as a carbon credit to someone else, the buyer should not also claim it, so agree in writing who claims what.

## Illustrative example: 500 hectares under AWD

- Baseline: 0.85 kg CH4 per ha per day (IPCC 2019 Refinement default for South Asia, continuously flooded, no organic amendments) x 120 days (assumed season) = 102 kg CH4 per ha
- AWD: 102 x 0.55 = 56.1 kg CH4 per ha; reduction 45.9 kg CH4 per ha
- In CO2e at AR5 GWP 28: 45.9 x 28 = 1,285.2 kg CO2e per ha
- Extra N2O: 120 kg N (assumed) x (0.005 minus 0.003) = 0.24 kg N2O-N x 44/28 = 0.377 kg N2O x 265 = 99.9 kg CO2e per ha
- Net: 1,285.2 minus 99.9 = 1,185.3 kg CO2e per ha; x 500 ha = 592,650 kg, about 593 t CO2e
- Per tonne of paddy at an assumed 4.0 t per ha: 1,185.3 / 4.0 = 296 kg CO2e less

Season length, nitrogen rate and yield are assumptions; measured baselines or organic amendments change the result. AR5 GWPs are used throughout.

## What Senseible does here

Senseible reads the mill's own electricity bills and fuel invoices into a fingerprinted Scope 1 and 2 record, the processing part of the rice footprint. Field water records for AWD are kept by the farmer programme.

- [Rice procurement Scope 3 emissions](https://senseible.earth/answers/rice-procurement-scope-3-emissions)
- [Sustainable Rice Platform GHG requirements](https://senseible.earth/answers/sustainable-rice-platform-ghg-requirements)
- [Regenerative agriculture Scope 3 claims](https://senseible.earth/answers/regenerative-agriculture-scope-3-claims)

Sources: [2019 Refinement to the 2006 IPCC Guidelines, Volume 4: Chapter 5, Tables 5.11 and 5.12 (rice methane); Chapter 11, Table 11.1 (direct N2O)](https://www.ipcc.ch), [GHG Protocol Corporate Value Chain (Scope 3) Standard](https://ghgprotocol.org/corporate-value-chain-scope-3-standard)

Last reviewed 2026-10-19. Buyer programmes may set their own evidence rules for AWD claims; check the buyer's current requirements.