Rice Methane Reduction

Methane (CH₄) is a potent greenhouse gas (GHG) with a 100-year global warming potential (GWP) 27.9 times that of carbon dioxide¹, making it a critical focus for near-term climate mitigation. Rice cultivation is one of the largest sources of methane, responsible for approximately 8% of total human-generated methane emissions; effectively 30 million tonnes of methane per year (equivalent to 840 million tonnes of CO₂e annually)². With over 170 million hectares of rice harvested worldwide each year, the scale of this emission source—and the corresponding mitigation opportunity—is substantial.

Alternate wetting and drying (AWD) is a water management practice that introduces one or more controlled drainage events during the rice growing season, temporarily lowering the water table and allowing the soil to aerate periodically, thus interrupting the anaerobic conditions that sustain methane creation. Current research consistently demonstrates that non-continuous flooding practices reduce methane emissions by 40–50% on average, with the magnitude of reduction depending on drainage frequency, duration, soil type, organic amendment practices, and climate conditions^3,4. Critically, when implemented according to established agronomic guidelines—including maintaining the field water level ≤ 15 cm below the soil surface and timing drainage to avoid moisture-sensitive crop growth stages—AWD maintains or improves rice yields while simultaneously reducing water consumption by 15–30%^5,6.

This Protocol establishes the requirements and standards for quantifying, reporting, and verifying greenhouse gas emission reductions achieved through the adoption of alternative water management practices in irrigated rice cultivation. It provides a consistent framework for Projects seeking to generate high-integrity Credits for methane emission reductions, ensuring that credited reductions are real, additional, independently verified, and conservatively quantified. To that end, this Protocol describes how Projects must establish baselines, monitor water management practices, measure or estimate methane and nitrous oxide fluxes, and account for project life-cycle emissions to make a full accounting of the climate benefits. This Protocol also defines project eligibility, stratification, and emission factor determination requirements, drainage verification procedures, and uncertainty quantification.

This Protocol supports Projects at varying scales, from smallholder farmer aggregation programmes covering hundreds of hectares to large-scale irrigation district interventions. It incorporates a flexible quantification approach that balances measurement precision with practical feasibility: direct field measurement via the closed-chamber method provides the highest accuracy for Projects with dedicated measurement infrastructure, while country-specific emission factors and IPCC default values enable participation by Projects in regions where direct measurement capacity is limited. This approach is designed to be inclusive without compromising scientific rigour, applying progressively larger uncertainty deductions to lower-tier quantification methods to maintain conservative crediting across all project types.

This Protocol relies on and is intended to be compliant with the following standards and protocols:

• The Isometric Standard
• ISO 14064-2: 2019 Greenhouse Gases Part 2: Specification with guidance at the project-level for quantification, monitoring, and reporting of greenhouse gas emission reductions or removal enhancements

Additional reference standards that inform the requirements and overall practices incorporated in this Protocol include:

• ISO 14064-3: 2019 Greenhouse Gases Part 3: Specification with Guidance for the Verification and Validation of greenhouse gas statements
• ISO 14040: 2006 Environmental Management Lifecycle Assessment Principles & Framework
• ISO 14044: 2006 Environmental Management Lifecycle Assessment Requirements & Guidelines

Protocols and Methodologies that were assessed as part of a literature review during the development of this Protocol include:

• Methane Emission Reduction by adjusted Water management practice in rice cultivation, v2.1, Gold Standard, 2025
• Methane Emission Reduction by Water Management in Rice Paddy Fields, Japan-Philippines Joint Crediting Mechanism Approved Methodology PHAM004, v1.0
• VM0051 Improved Management in Rice Production Systems, v1.0, Verra, 2025
• GHR005 Methodology for Assessing Emission Reductions from Rice Cultivation, v1.0, Global Heat Reduction, 2025
• Rice Cultivation Project Protocol, v1.1, Climate Action Reserve, 2013

This Protocol was developed based on the current state-of-the-art, publicly available science regarding reducing GHG’s in rice cultivation. This Protocol aims to be scientifically stringent and robust. We recognize that some requirements may exceed the status quo in the market and that there are numerous opportunities to improve the rigor of this Protocol. Key future improvements to the Protocol are outlined in Appendix B.

Additionally, this Protocol will be reviewed when there is an update to published scientific literature, government policies, or legal requirements that would affect net emissions quantification or the monitoring guidelines outlined in this Protocol, or at a minimum of every 2 years.

To qualify for crediting under this Protocol, a Project must meet all of the following conditions.

This Protocol is globally applicable to rice cultivation projects on irrigated, lowland rice fields.

Project rice fields must be equipped with controlled irrigation facilities such that, in both dry and wet seasons, the Project Proponent can establish the appropriate dry and flooded conditions required by the project activity.

Rice cultivation in the project area must be predominantly characterized by irrigated, flooded fields for an extended period during the growing season. Fields whose water regimes are classified as upland, rainfed, or deep water are not eligible under this Protocol.

The baseline on-season water regime scenario must correspond to one of the following conditions:

• Continuously flooded rice cultivation: The baseline water management practice is continuously flooded during the rice growing season, which is the predominant practice in the project region.
• Single drainage with continuous flooding: In regions where a single mid-season drainage event is already standard practice, the baseline may reflect this existing practice. In such cases, only the incremental change from single drainage to multiple drainage (AWD) is eligible for crediting.

Projects must indicate which scenario best describes the baseline conditions that reflect Business As Usual (BAU).

• In addition to the on-season water regime, the description of the baseline scenario must also include pre-season water management, organic amendment practices, the typical number of growing seasons, and rice variety selection.
• The baseline on-season water regime must be demonstrated using a credible source, which may include representative surveys, national or sub-national data, peer-reviewed literature, or project-level records.

To be eligible for crediting, each enrolled field must provide evidence that the field was under active rice cultivation with an eligible baseline on-season water regime. Under this protocol a field is defined as the smallest unit across which management if homogeneous. A single credible evidence source is sufficient. At minimum, the following must be evidenced:

• The field was cultivated under one of the eligible baseline conditions within five years immediately preceding the initiation of the project activity.
• The baseline condition must be different than the proposed activities.
• The number of seasons per year the field was cultivated for rice was consistent with the baseline period or with regional practices.
• The project area must not have been cleared of native ecosystems within the 10 years immediately preceding the project start date.

Acceptable forms of evidence include, but are not limited to:

• remote sensing data (e.g., SAR imagery for flooding patterns, vegetation indices for crop cycles);
• field-level management records, where available;
• farmer or community attestation referencing the specific field; and/or
• if none of the above are available, national or subnational assessments of common practice.

Isometric retains the right to use historical remote sensing data to confirm that the baseline scenario and historical land use have been accurately described.

Where a project activity involves the introduction of a rice cultivar that has not previously been cultivated in the project region, the Project Proponent must demonstrate that the newly introduced cultivar does not necessitate material changes to existing land management practices beyond those required by the eligible project activity itself.

A Project must involve one or more of the following activities that reduce anaerobic decomposition of organic matter during rice cultivation and thereby reduce methane generation:

• Single or multiple drainages: Changing the water regime during the rice cultivation period from continuously flooded practices to intermittently flooded conditions through one or more controlled drainage and re-flooding cycles, including alternate wetting and drying (AWD).
• Transition from transplanted to dry direct-seeded rice (DSR): Switching from transplanted rice cultivation with continuously flooded fields to dry direct-seeded rice, where the reduced flooding period arises from the non-flooded conditions required after sowing until seedling establishment.

A drainage event is defined as a period during which the field water level falls to between 5 and 15 cm below the soil surface (or between -10 and -20 kPa if using digital water sensors) before re-flooding is initiated. Only drainages that were not present in the baseline are considered additional.

During the project period, each field must maintain the same number of rice cultivation seasons per year as was practiced during the baseline period.

• Any change to the crop rotation or number of growing seasons per year under project activities must be justified by factors other than Carbon Finance and must remain consistent with common agricultural practices in the region.

All fields implementing drainage-based project activities must monitor water levels during each drainage event to evidence that the project activity has occurred and to ensure that drainage does not exceed the threshold at which yield loss and associated leakage emissions become a material risk⁷.

For each drainage event, the field must record the water level below the soil surface at its lowest point before re-flooding. Two measurement methods are acceptable:

1. Field water tube: a perforated pipe installed vertically in the field that allows observation of the water table relative to the soil surface^8,9. The pipe should be graduated or marked at regular intervals (e.g., every centimetre) to allow accurate reading of the water depth below the soil surface.
2. Digital water-level sensor: an automated sensor installed in the field that continuously logs either (a) water table depth relative to the soil surface, or (b) soil water potential. Where soil water potential is measured, a threshold of -20 kPa shall be used as the re-flooding trigger, consistent with the widely cited safe AWD threshold for avoiding yield-limiting water stress^6,10.

Readings must be taken at the lowest point reached before re-flooding for each drainage event and recorded alongside the date, time, and unique field ID. Projects must also submit geotagged photos of the field water tube measurement at this lowest point for all drainage events for at least 5% of fields in the Reporting Period.

• If the recorded water level at the point of re-flooding exceeds 15 cm below the soil surface or below -20 kPa, at any drainage event during a Reporting Period, Projects must evidence that the yield of the affected field did not decrease by more than 3% than anticipated. If yield loss exceeds 3% or cannot be evidenced, that field is ineligible for crediting.
• Exemptions for drainages exceeding 15 cm below the soil surface or below -20 kPa may be granted if Projects evidence that such drydowns do not negatively affect yields and is approved by a national agronomist.

Documentation requirements for water level monitoring are specified in the monitoring provisions in Section 9.3 of this Protocol.

The application of soil amendments can reduce the methane potential of rice paddies in addition to water-saving irrigation practices. Biochar reduces CH₄ dynamics by altering soil aeration, microbial community composition, and organic carbon dynamics^11,12. Methanotrophs are a novel intervention involving the application of methane-oxidizing bacteria that enhance CH₄ oxidation in the soil¹³. Application of methane-reducing amendments such as biochar or methanotrophs is permitted when co-deployed with eligible activities described in Section 4.2. When these amendments are applied in treated fields, quantification of the Project's methane reduction using default emission factors will under-count the effective reduction; direct measurements will be subject to the uncertainty screening in Section 8.6.2, so total Credits issued remain conservative.

Where biochar or methanotrophic bacteria are applied as a project activity, the Project Proponent must disclose the use of such amendments when describing project activities, and must stratify the project area to distinguish areas that receive these amendments from areas that do not, as set out in the Alternative Application conditional stratification criterion in Section 7.2.

The following topics are covered briefly in this Protocol due to their inclusion in the Isometric Standard, which governs all Isometric Protocols. See in-text references to the Isometric Standard for further guidance.

For each specific Project to be evaluated under this Protocol, the Project Proponent must document project characteristics in a Project Design Document (PDD) as outlined in Section 3.2 of the Isometric Standard. The PDD will form the basis for project verification and evaluation in accordance with this Protocol, and must include consideration of processes unique to each Project, such as:

• a description of the baseline conditions as described in Section 4.1.1;
• a description of the stakeholder engagement plan in adherence with Section 6.2.1; including a description of the training and technical support provided
• a description of the mitigation plan according to the environmental and social risk assessment in adherence with Section 6.1, including an accompanying robust monitoring plan to ensure efficacy;
• a description of the quantification strategy for gross CO₂e reduction following Section 8.3.1; and
• a description of all measurements and methods used to quantify processes relevant to the calculation of net CO₂e reduction.

Projects must be validated and net CO₂e removals verified by an independent third party, consistent with the requirements described in this Protocol as well as in the Isometric Standard.

The VVB must adhere to these requisite components:

• Verify that the Project is compliant with requirements outlined in the Isometric Standard.
• Verify that the Environmental & Social Safeguards outlined in Section 6 are met.
• Verify that the quantification approach adheres to the requirements of Section 8, including the demonstration of required records.

The threshold for Materiality, considering the totality of all omissions, errors, and mis-statements, is 5%, in accordance with the Isometric Standard.

Verifiers should also verify the documentation of uncertainty of the GHG statement as required by the Isometric Standard.

Qualitative Materiality issues may also be identified and documented, such as:

• control issues that erode the verifier’s confidence in the reported data;
• poorly managed documented information;
• difficulty in locating requested information;
• noncompliance with regulations indirectly related to GHG emissions and reductions.

Project Validation and Verification must incorporate site visits to project facilities, namely rice paddies, in accordance with the requirements of ISO 14064-3, 6.1.4.2. This is to include, at a minimum, site visits to the project site during Validation and initial Verification. Validators should, whenever possible, observe project operations to ensure full documentation of process inputs and outputs through visual observation (see the Isometric Standard).

Additional site visits may be required if there are substantial changes to field operations over the course of the Validation period or if deemed necessary by Isometric or the Validation and Verification Bodies (VVBs). Site visit plans are to be determined according to the VVB’s internal assessment, in consultation with Isometric.

Verifiers and validators must comply with the requirements defined in the Isometric Standard. In addition, VVB teams must maintain and demonstrate expertise associated with the specific technologies of interest.

All VVBs are approved by Isometric independently and impartially based on alignment with Conflict of Interest policies, rotation of VVB policies, oversight on quality and the following requirements:

• VVBs must be able to demonstrate accreditation from one of the following:
  • an International Accreditation Forum member against ISO 14065 or other relevant International Standards Organization (ISO), including but not limited to ISO 14034, ISO 17020, ISO 17029; or
  • a relevant governmental or intergovernmental regulatory body.
• Alternatively, VVBs may be approved on a case-by-case basis if they are able to demonstrate to Isometric that they satisfy all required Verification needs and competencies required for the relevant Protocol and follow the guidelines of ISO 19011 or other relevant standards.

Greenhouse gas reduction or avoidance can often be a result of a multi-step process, with activities in each step managed and operated by a different operator, company, or owner. When there are multiple parties involved in the process, and to avoid double-counting of net CO₂e reductions, a single Project Proponent must be specified contractually as the sole owner of Credits. Contracts must comply with all requirements defined in the Isometric Standard.

The Project Proponent must be able to demonstrate additionality through compliance with the Isometric Standard. The counterfactual scenarios and baselines utilized to assess additionality must be project-specific, and are described in Section 7.3 of this Protocol.

Additionality determinations must be reviewed and completed at project validation, as well as in the event that significant changes to project operating conditions, such as the following:

• regulatory requirements or other legal obligations for project implementation change or new requirements are implemented;
• project financials indicate Carbon Finance is no longer required, potentially due to, for example:
• sale of co-products that make the project activities viable without Carbon Finance;
• reduced rates for capital access.
• Any review and change in the determination of additionality will not affect the availability of Carbon Finance and Credits for the current or past Crediting Periods, but if the review indicates the Project has become non-additional, this will make the Project ineligible for future Credits.

Rice methane reduction activities—particularly alternate wetting and drying (AWD) and dry seeding—generate co-benefits beyond greenhouse gas mitigation, such as substantial reductions in irrigation water use^10,14. Such co-benefits may qualify for separate payments under agricultural conservation or water stewardship schemes¹⁵. Payments for multiple ecosystem services resulting from a single management practice is known as stacking^16,17.

Projects must disclose any expected or received stacked payments made to the Project Proponent or the landowner from additional ecosystem services provided as a result of project activities at Validation and all Verifications.

• Stacked services must be a distinct, separate ecosystem benefit and does not constitute a Removal or Reduction that may be double-counted as defined in the Isometric Standard.

Should such alternative funding streams arising from project activities make Carbon Finance no longer necessary to perform the Removal or Reduction activity, the Project will no longer be considered additional (Section 5.4) and thus will not be eligible for Credits.

The Project Proponent must demonstrate that without Carbon Finance the project activity is not Common Practice, in accordance with the requirements defined in the Isometric Standard.

The analysis must be conducted at the state or provincial level (or equivalent second-order administrative jurisdiction) in the country where the Project is being developed. Where data is unavailable at this level, the analysis may be conducted at the national level with justification. Where the Project spans multiple jurisdictions, the analysis must be conducted separately for each, and the penetration rate threshold must be satisfied in every jurisdiction in which the Project operates. All adoption is counted regardless of whether the adopting fields are registered under a carbon crediting programme.

Evidence must be drawn from publicly available information, including but not limited to:

• agricultural census or government survey data;
• peer-reviewed scientific literature;
• independent research data;
• grower surveys conducted within the project region;
• reports or assessments from industry associations; and/or
• remote sensing datasets.

As defined by the Isometric Standard, the proposed project activity is considered to demonstrate Common Practice additionality where the market penetration rate is below or equal to 20% of similar activities conducted without Carbon Finance.

The uncertainty in the overall estimate of net CO₂e impact as a result of the Project must be accounted for. The total net CO₂e impact for a specific Reporting Period must be conservatively determined, and Projects must conduct an uncertainty analysis for the net CO₂e impact calculation in compliance with requirements outlined in the Isometric Standard.

Projects must report a list of all key variables used in the net CO₂e removal calculation and their uncertainties, as well as a description of the uncertainty analysis approach, including:

• required measurements used for net CO₂e calculation;
• emission factors utilized, as published in public and other databases used;
• estimations generated from the use of gas or flux chambers;
• laboratory analyses.

The uncertainty information should at least include the minimum and maximum values of each variable that goes into the net CO₂e calculation (see Section 8.2 for more details). More detailed uncertainty information should be provided if available, as outlined in the Isometric Standard.

In addition, a sensitivity analysis that demonstrates the impact of each input parameter’s uncertainty on the final CO₂e uncertainty must be provided. Details of the sensitivity analysis method must be provided such that a third party can reproduce the results. Input variables may be omitted from an uncertainty analysis if they contribute to a 1% change in the net CO₂e removal. For all other parameters, information about uncertainty must be specified.

In accordance with the Isometric Standard, all evidence and data related to the underlying quantification of net CO₂e removal and environmental monitoring will be available to the public through Isometric’s Science Platform. That includes:

• Project Design Document
• GHG Statement
• Measurements taken
• Model specifications and output
• Emission factors used
• Scientific literature used

The Project Proponent can request certain information to be restricted (only available to authorized Buyers, the Registry and VVB) where it is subject to confidentiality. However, that does not apply to any numerical data produced or used as part of the quantification of net CO₂e impact.

In addition, in compliance with FAIR Principles, the Project Proponent should publicly disseminate deployment data that is relevant to scientific research, such as through open data repositories.

Following the Isometric Standard, Credits issued under this Protocol are contingent on the implementation, transparent reporting, and independent verification of comprehensive safeguards. Isometric takes a holistic approach to Environmental and Social Safeguarding (ESS). Risks associated with project activities must be weighed alongside risks of climate change to support responsible innovation.

Environmental and Social Safeguards must include, but are not limited to, the following Integrity Council for the Voluntary Carbon Market (ICVCM) Core Carbon Principles:

• Compliance: The introduced cultivation practices, including specific technologies and crop protection products, must comply with all national and local laws, regulations, and policies.
• Risk Identification: Project Proponents must assess the potential environmental and social risks of project activities, in adherence with the Isometric Standard. Risk identification, impact assessment and mitigation plans must include, at a minimum, a discussion of ownership disputes over land or carbon rights, labor rights and working conditions, land acquisition and involuntary resettlement, land abandonment, and environmental and social justice, including human rights and indigenous land rights.
• Impact Assessment and Mitigation: Project Proponents must conduct an impact assessment and strategy for mitigation for each risk identified above. The impact of potential harms must be considered along with the positive climate benefit and potential co-benefits of projects. Impact assessments may be qualitative or quantitative.
• Monitoring and Adaptive Management: Implementation of risk mitigation measures must also be accompanied by a robust monitoring plan to ensure efficacy. Project Proponents must preemptively develop a remediation plan in the case that the identified risks occur and result in harm to the environment or society.

In accordance with the Isometric Standard, Project Proponents must demonstrate active stakeholder engagement throughout project planning and operation, ensuring that all risk mitigation strategies contribute to sustainable project outcomes. Local stakeholders may contribute an in-depth understanding of the project area and operations, and provide invaluable insights and recommendations on potential risks, necessary safeguards, and specific monitoring needs.

Projects must develop a Stakeholder Engagement Plan in accordance with the requirements outlined in the Isometric Standard. The plan and supporting documentation, including evidence of meetings or other forms of engagement, must be submitted in the PDD.

The Project Proponent or participants must demonstrate legitimate legal tenure or right of use over all lands included in the project area, in addition to demonstrating the eligible baseline conditions for each field (see Section 4.1.1). This requirement ensures that the Project Proponent or participants have the authority to implement project activities, make cultivation management decisions, and claim the resulting emission reductions. Acceptable forms of evidence and the verification process are specified in Section 9.2.1.

A field may change ownership, tenant occupancy, or management during a Reporting Period and remain eligible for crediting if:

• the participation contract is transferred from the outgoing to the incoming project participant;
• the Project Proponent informs Isometric of the change in ownership before issuing Credits;
• the incoming project participant has been provided training and technical support (see Section 6.2.1.3); and
• implementation of the project activity continues without change until the end of the Reporting Period.

Where any of these criteria are not met, the field forfeits the opportunity to generate Credits for the Reporting Period during which the change occurs.

Projects must document the enrollment of each participating farmer or project participant. Required documentation and the verification process are specified in Section 9.2.2.

Ensuring that participating farmers receive a fair and transparent share of the financial benefits generated from carbon Credits is essential to the integrity and long-term sustainability of the Project.

Projects must describe the benefit-sharing mechanism with enrolled farmers. This should include:

• the basis for farmer compensation (e.g., per-hectare payment, per-credit share, in-kind support, or a combination thereof); and
• how benefits are distributed.

Projects must provide training and technical support to all participating farmers, covering field preparation, irrigation and drainage management, and water level monitoring.

• Training must be documented so that it may be verified (e.g., attendance records, on-site visit logs, photographic evidence).
• Projects must ensure that farmers are equipped, through direct capability or experienced assistance, to monitor water levels and re-flood fields at the appropriate time to prevent potential reductions in rice yields (Section 7.4).
• Training should include a description of any risks associated with the Project.

The scope of this Protocol includes GHG sources, sinks and reservoirs (SSRs) associated with a Rice Methane Reduction Project.

A cradle-to-grave GHG Statement must be prepared encompassing the GHG emissions relating to the activities outlined within the system boundary.

GHG emissions and reductions associated with the Project may be direct emissions from a process, or indirect emissions from combustion of fuels, electricity generation, or other sources. Emissions must include all GHG SSRs within the system boundary, from the construction or manufacturing of each physical site and associated equipment, closure and disposal of each site and associated equipment, and operation of each process, including embodied emissions of equipment and consumables used in the Project. The Project Proponent is responsible for identifying all sources of emissions directly or indirectly related to project activities.

As noted in Section 7.3, the baseline scenario assumes continuous flooding of irrigated rice paddies in the absence of any project activities, producing methane through anaerobic decomposition of organic matter.

Any emissions from sub-processes or process changes that would not have taken place without the Project must be fully considered in the system boundary. Any activity that ultimately leads to the issuance of Credits should be included in the system boundary.

The system boundary must include all relevant GHG SSRs controlled and related to the Project, including but not limited to the SSRs set out in Table 1. If any GHG SSRs within Table 1 are deemed not appropriate to include in the system boundary, they may be excluded provided that robust justification and appropriate evidence are provided in the PDD.

Table 1 System Boundary

The system boundary accounts for emissions that are additional in the project scenario relative to the baseline scenario. Where an SSR exists in both the baseline and project scenarios, only the incremental change in emissions attributable to the project activity must be quantified. For example, land preparation activities that occur at the same frequency and intensity under both continuous flooding and AWD regimes do not generate additional emissions and need not be separately quantified, provided the Project Proponent demonstrates that no material change has occurred. Conversely, drainage and re-irrigation pumping represents a new or intensified activity under AWD that would not occur at the same level under continuous flooding, and the associated emissions must be fully accounted for. The Project Proponent must justify any determination that an SSR is materially unchanged between the baseline and project scenarios.

Where the Project Proponent claims an SSR is materially unchanged between the baseline and project scenarios, the following evidence must be provided in the PDD:

• evidence that the activity associated with the SSR was occurring as part of routine cultivation operations prior to Project activities. Where the baseline practice associated with the SSR is already documented under Section 4.1.1, that documentation satisfies this requirement. Otherwise, the Project Proponent must provide either:
  • historic records documenting the activity prior to the project start date (e.g., farmer logbooks, management records, applicator invoices, equipment-use records, or equivalent documentation); or
  • a signed affidavit from the relevant operator (e.g., the farmer, land manager, contractor, or applicator) confirming the activity was part of routine cultivation operations prior to the Project; and
• in all cases, a signed affidavit from the relevant operator confirming that the scope, frequency, equipment, route, payload, and intensity of the activity are not materially altered as a result of project activities, and that the activity would have continued at a comparable level absent the Project.

Miscellaneous GHG emissions are those that cannot be categorized by the GHG SSR categories provided in Table 1. The Project Proponent is responsible for identifying all sources of emissions directly or indirectly related to project activities and must report any outside of the SSR categories identified as miscellaneous emissions.

In line with the GHG Accounting Module v1.1, the Project must:

• Consider all GHGs associated with SSRs, in alignment with the United States Environmental Protection Agency’s definition of GHGs, which includes: carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and fluorinated gases such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6), and nitrogen trifluoride (NF₃). For CO₂ stored, only CO₂ must be included as part of the quantification. For all other activities, all GHGs must be considered. For example, the release of CO₂, CH₄, and N₂O is expected during diesel consumption;
• Quantify emissions in tonnes CO₂ equivalent (t CO₂e) using the 100-year Global Warming Potential (GWP) for the GHG of interest, based on the most recent volume of the IPCC Assessment Report (currently the Sixth Assessment Report); and
• Consider Materiality of SSRs in line with Isometric requirements.

AWD practices may lead to minor losses of soil organic carbon (SOC) due to accelerated aerobic decomposition during drying phases. When fields are drained during AWD cycles, oxygen penetration enables aerobic respiration, which can proceed at substantially higher rates, as evidenced by CO₂ emission pulses observed during drainage events. However, the magnitude of this SOC loss is small, estimated at approximately 0.6-1.3% per year¹⁸, and is generally lower under Safe AWD practices compared to more severe drying regimes. Critically, any SOC loss associated with AWD is minor relative to the climate benefit achieved through methane emission reductions, given the substantially higher global warming potential of CH₄. For these reasons, this methodology acknowledges SOC loss as a potential trade-off of AWD implementation but does not require its explicit quantification as a separate line item. Instead, the effect is conservatively accounted for within the overall uncertainty discount applied to credited emission reductions, ensuring that net climate benefits are not overstated.

Black carbon (BC) is a short-lived climate pollutant emitted during the incomplete combustion of biomass, including the open burning of rice straw and other crop residues. BC absorbs solar radiation and contributes to atmospheric warming, with a GWP100 estimated at 342¹⁹. This represents a substantial downward revision from earlier estimates (e.g., 900 in Bond et al., 2013²⁰), reflecting advances in the understanding of BC's atmospheric lifetime, rapid adjustments to radiative forcing, and aerosol-cloud interactions. BC emissions from biomass burning are excluded from the project boundary under this protocol.

BC's climate impact remains highly uncertain. The total effective radiative forcing of BC, inclusive of aerosol-radiation interactions, aerosol-cloud interactions, rapid adjustments, and deposition on snow and ice, is estimated at 0.11 W/m² with a range of 0.20 to 0.42 W/m²¹⁹. This range includes both warming and cooling outcomes. The GWP100 for BC has been revised downward in each successive assessment since Bond et al. (2013)²⁰, from 900 to 658²¹ to 342¹⁹. The magnitude and direction of this uncertainty do not support inclusion of BC in Isometric's emission reduction accounting at this time.

Additionally, open biomass burning emits BC alongside organic carbon and sulfate aerosols, both of which exert a cooling effect by scattering incoming solar radiation. The net radiative impact of a change in burning practice depends on the ratio of warming to cooling species in the smoke, which varies with combustion conditions, moisture content, and fuel type. Rice straw burning is characterised by relatively high smoldering fractions, producing elevated organic carbon to black carbon ratios. The net aerosol radiative effect of avoided biomass burning in rice systems is therefore ambiguous and potentially close to zero^22,23,24.

This exclusion is conservative. Omitting BC from the project boundary results in a lower estimate of the project's total climate benefit than would be obtained by including it, and therefore does not risk over-crediting. Should future scientific assessments materially revise BC's effective radiative forcing upward, this exclusion may be revisited in subsequent protocol versions.

The Project Proponent must stratify the project area into distinct strata that are internally homogeneous with respect to the criteria defined in this section. Stratification ensures that emission factors used for baseline estimation and crediting calculations are representative of the conditions within each stratum, and that within-stratum variability does not systematically bias the quantification of emission reductions.

Each stratum must be defined by a unique combination of the mandatory criteria listed below. Additional stratification by conditional and optional criteria is required or recommended as described below. Data source guidance and stratum documentation requirements are specified in Section 9.1.1.1.

Required Stratification Criteria
All Projects must stratify by the following criteria. These criteria correspond directly to the scaling factors in the 2019 IPCC²⁵ emission factor equation for CH₄ emissions from rice cultivation:

• Water regime (on-season): The project area must be stratified by the water management regime practiced during the cultivation season. The on-season water regime is the primary determinant of anaerobic conditions and CH₄ production. Because drainage interventions directly modify this parameter, changes in water regime classification between the baseline and project scenario are the principal mechanism through which emission reductions are generated.
• Water regime (pre-season): The project area must be stratified by the duration of flooding prior to the cultivation season. Categories must align with the pre-season water management classifications in IPCC 2019 Refinement²⁵, Table 5.13: flooded for more than 30 days, non-flooded for fewer than 180 days prior to cultivation (short drainage), or non-flooded for 180 days or more prior to cultivation (long drainage). The 180-day threshold is intended to distinguish single-cropping systems from double-cropping systems.
• Organic amendment: The project area must be stratified by the type of organic amendment applied to paddy soils. Types must be classified using the approved conversion factors for organic amendments ($CFOA_a$) (see Appendix A). The following categories must be distinguished: straw incorporated shortly before cultivation (on-season), straw incorporated long before cultivation (off-season), green manure, farmyard manure, compost, and/or no organic amendment. Only projects using these amendment types are eligible.
• Organic amendment rate: The project area must be stratified by the application rate of organic amendments. Because the relationship between application rate and emissions is non-linear, grouping fields with materially different application rates within a single stratum will systematically bias the emission estimate. Where multiple application rates exist within a stratum, the Project Proponent must apply the most conservative (lowest) rate to the entire stratum.
• Cultivation period: All fields within any given stratum must be of a similar cultivation period length. If the Reporting Period spans multiple cropping seasons, all fields within a stratum must be cultivated for the same seasons.

Conditional Stratification Criteria
The following criteria must be applied as stratification parameters when the specified conditions are met. Where the conditions are not present, these criteria are not required.

• Soil type (taxonomy): Projects located in regions known to contain Histosols, Andosols, or Thionic (acid sulfate) soils must screen the project area for the presence of these soil types and maintain separate strata for any areas classified under these taxonomic groups. These soil types have emission dynamics that are not fully captured by other stratification criteria: Histosols contain very high organic matter, leading to elevated substrate availability; Thionic soils exhibit sulfate-mediated methanogenesis suppression; and Andosols have unique water retention properties that affect redox dynamics. Where the screening confirms the absence of these soil types within and immediately adjacent to the project boundary, the Project Proponent must document this finding but no additional stratification is required.
• Other methane mitigation amendments: Where biochar or methanotrophic bacteria are applied as a project activity, the project area must be stratified to distinguish areas that receive alternative amendments from areas that do not.

Recommended Stratification Criteria
It is recommended that the Project Proponent further stratify the project area using the following criteria. Additional stratification may improve the accuracy of emission estimates by reducing within-stratum variability.

• Soil pH: It is recommended that the project area be stratified into strongly acidic (4.5), moderately acidic (4.5-5.5), or near-neutral to alkaline (5.5) soil. Soil pH influences microbial community composition and methanogenesis rates. Stratification by pH is particularly recommended for Projects operating on strongly acidic soils where methanogenesis dynamics differ materially from near-neutral soils. If a Project includes liming soils, this should also be considered as part of stratifying the project area by soil pH.
• Soil organic carbon (SOC): It is recommended that the project area be stratified into low (1%), moderate (1-3%), or high (3%) SOC stocks. Higher SOC provides greater substrate for methanogens and is associated with elevated baseline CH₄ emissions.
• Soil texture: It is recommended that the project area be stratified by proportion of soil clay content, as clay influences the mineral-associated organic carbon pools and methanotroph abundance²⁶. Furthermore, texture affects water retention and hydraulic conductivity, influencing the degree and duration of anaerobic conditions. It is recommended that Projects stratify areas with < 20%, between 20% and 50%, and > 50% clay content.
• Climate: Projects should stratify the project area on climate using the 2nd level 1990-2020 Köppen-Geiger climate classification maps (version 3)²⁷. The Köppen-Geiger system classifies climate based on temperature and precipitation regimes, both of which influence soil methanogenesis rates in flooded rice systems.

Where a project area spans multiple potential sub-categories within a stratum but monitoring data cannot distinguish between them, the most conservative parameter values must be applied (i.e., the combination of parameters that would produce the lowest net reductions). The lowest value is the most conservative, as that minimizes the potential expected emissions that may be reduced. Specifically:

• For the organic amendment type, where multiple types of amendments are used within a stratum, the stratum is classified as the amendment with the lowest $CFOA_a$ to conservatively estimate the potential emissions and their reduction.
• For the organic amendment rate, where multiple rates are present within a stratum, the lowest rate must be used to calculate the organic amendment scaling factor for the entire stratum.
• For the water regime, where baseline water management practices vary within a stratum but cannot be resolved, the water regime associated with the lowest baseline emissions must be applied.
• For any continuous variable used as an optional stratification criterion, within-stratum values should be reasonably homogeneous. Where significant heterogeneity exists, the Project Proponent should either create additional strata or apply the most conservative value.

Strata definitions must be reviewed at each Crediting Period renewal. If management practices or site conditions have changed such that a stratum is no longer internally homogeneous with respect to the mandatory criteria, the Project Proponent must update the stratification and document the changes.

The baseline scenario represents the business-as-usual condition, describing the expected methane flux that would occur in the absence of the Project. Under this Protocol, the baseline must correspond to one of the following conditions:

• Irrigated, continuously flooded rice cultivation throughout the growing season, with end-of-season drainage only; or
• In regions where single drainage is demonstrably the established practice, single drainage with continuous flooding, with appropriate adjustment to baseline emission factors.

The eligibility requirements for baseline conditions are defined in Section 4.1.1.

The baseline quantification accounts for CH₄ emissions from methanogenesis in soil only. Under continuously flooded conditions, rice soils remain persistently anaerobic, suppressing nitrification and limiting N₂O production to limiting levels. All other GHG sources are accounted for entirely as project-side emissions, where only the additional or incremental emissions attributable to the project activity are quantified (see Section 8.4).

Leakage emissions occur when project activities cause a secondary effect leading to increased GHG emissions that occur outside the system boundary of Projects. Reductions in rice production yield as a result of the project activities would result in a reduction of the supply of rice. Changes to the supply and demand equilibrium cause other market actors to shift their activities, leading to potential land conversion. This type of leakage is known as market or “indirect” leakage because its effects cannot be isolated and measured directly. Quantifying the likelihood and potential magnitude of market leakage is complex and relies heavily on modeling and available literature.

Under the project eligibility conditions on water levels outlined in Section 4.2.1, there are negligible risks to yield impacts^10,28,²⁹. Isometric deems leakage risks to be de minimis so long as these conditions are met.

The Reporting Period, $RP$, represents an interval of time over which reductions are calculated and reported for verification. The total net CO₂e reduction is calculated using a series of measurements for a specified Reporting Period.

GHG emission calculations must include all emissions related to the project activities that occur within the Reporting Period. This includes:

• any emissions associated with project establishment allocated to the Reporting Period,
• any emissions that occur within the Reporting Period, and
• any anticipated emissions that would occur after the Reporting Period that have been allocated to the Reporting Period.

Projects must confirm the length of their Reporting Period as either a single cropping season, multiple cropping seasons, or 12 consecutive months.

• Reporting Periods should not exceed 12 consecutive months.
• When selecting the Reporting Period based on season(s), Projects must describe the expected months relevant for the season(s). Seasons, and thus Reporting Periods, may be of different lengths so long as they span the full anticipated cropping season.
• Seasons still growing at the beginning or end of a Reporting Period are not eligible for crediting in that Reporting Period.
• Reporting Periods may span multiple cropping seasons within 12 consecutive months.

Net CO₂e reduction from a Rice Methane Reduction Project for each Reporting Period, $RP$, must be calculated conservatively so as to give high confidence that the estimated net CO₂e was reduced. The net CO₂e reduction equation is:

$CO_2e_{Reduction,RP} =CO_2e_{Baseline,RP}-CO_2e_{Project,RP}$

(Equation 1)

Where:

• $CO_2e_{Reduction,RP}$ represents the net CO₂e reduction for the Reporting Period, $RP$, in tonnes of CO₂e.
• $CO_2e_{Baseline,RP}$ represents the net CO₂e emissions which would have occurred in the absence of the Project, over the Reporting Period, $RP$, in tonnes of CO₂e.
• $CO_2e_{Project,RP}$ represents the net CO₂e emissions from the associated project activities and Life Cycle Analysis (LCA) over the Reporting Period, $RP$, in tonnes of CO₂e.

Baseline emissions are summed across all strata within the Reporting Period using the following equation:

$CO_2e_{Baseline,RP}= \sum\limits_g (EF_{BL,g} \times A_g \times 10^{-3} \times GWP_{CH_4})$

(Equation 2)

Where:

• $EF_{BL,g}$ represents the baseline emission factor for stratum $g$ in kg CH₄/ha.
• $A_g$ represents the area of project fields in stratum g in season s, in hectares.
• $10^{-3}$ represent the conversion factor from kg CH₄ to tonnes CH₄.
• $GWP_{CH_4}$ represents the 100-year global warming potential of CH₄, 27.9¹.
• $g$ represents each individual stratum.

Emission factors must be determined for each stratum using one of the following approved methods. A project may employ different approaches for different strata, provided the requirements of each approach are met.

Method 1: Default Emission Factors

Projects may calculate methane emissions using default or country-specific parameters in combination with default scaling factors^25,30 (Appendix A). Note that emissions reductions determined using this Method will be subject to an additional uncertainty deduction outlined in Section 8.6.1.

The emission factor is calculated as:

$EF_g = EF_c \times SF_w \times SF_p \times SF_o \times t$

(Equation 3)

Where:

• $EF_g$ represents the emission factor for stratum $g$ in kg CH₄/ha.
• $EF_c$ represents the country-specific emission factor for continuously flooded fields without organic amendments, in kg CH₄/ha/day.
• $SF_w$ represents the scaling factor for the water regime during the cultivation period ($SF_w$ is 1.0 for continuous flooding).
• $SF_p$ represents the scaling factor for the pre-season water regime.
• $SF_o$ represents the scaling factor for organic amendments.
• $t$ represents the cultivation period for stratum $g$, in days.

The organic amendment scaling factor, $SF_o$, is calculated as follows:

$SF_o = (1+\sum \limits_a ROA_a \times CFOA_a)^{0.59}$

(Equation 4)

Where:

• $ROA_a$ represents the application rate of organic amendment type $a$, in dry weight for straw and fresh weight for others, in tonnes/ha.
• $CFOA_a$ represents the conversion factor for organic amendment type $a$.

If no organic amendments are applied, the value of $SF_o$ is 1.

If it is not possible to delineate the application rates for mixed amendment types, $ROA_a$ and $CFOA_a$ must be set to the lowest value to conservatively limit the potential methane that may be reduced (see Section 7.2.1).

Method 2: Direct Measurement

Instead of using default emissions factors that represent average estimates, Project Proponents may instead wish to directly measure emissions within the Project. Direct measurements impose a higher operational cost for Projects, but provide a higher confidence in their results and thus are subject to a different uncertainty deduction (see Section 8.6.2).

When directly measuring the methane flux within a stratum, Project Proponents establish one or more measurement clusters to directly quantify CH₄ emissions. In this Protocol, a measurement cluster is defined as the collection of fields and measurement locations that are targeted at quantifying methane reductions and uncertainty on a stratum level. Each measurement cluster consists of at least three reference fields, maintained under the baseline water management regime and three paired treatment areas. Both the reference fields and paired treatment areas must be located within the same stratum and must be representative of the conditions within that stratum or conservatively set with respect to all mandatory stratification criteria (see Section 7.2).

The following requirements apply when taking direct measurements:

• Measurements should be taken at matched time points between 08:00 and 12:00 across the reference fields and treatment areas so as to be comparable with most published estimates^31,32. Isometric will review any measurements taken outside of this window for material effects on measured emissions.
• Measurements must span a full cultivation season to capture temporal variability in CH₄ fluxes.

The seasonally integrated emission factor is calculated as the arithmetic mean of the reference field measurements collected over the growing season. The measurement methodology, equipment, calibration procedures, and data quality assurance protocols must be specified in the PDD and must follow the requirements set out in Section 9.4.

Every stratum over 10,000 ha should have at least one measurement cluster. For strata exceeding 25,000 hectares, one additional measurement cluster should be included for each additional 25,000 ha (or fraction thereof). Measurement clusters must be selected to capture the central tendency and variability of conditions within the stratum. The Project Proponent must document the rationale for cluster placement in the PDD.

Method 3: Transformed Measurement

Due to operational limitations, it may not be possible to measure CH₄ emissions in all strata within a Project. In such scenarios, Project Proponents may extrapolate their measurements to unmeasured strata with the same organic amendment instead of default emission factors (described in Method 1). Doing so may lead to uncertainty more reflective of field conditions.

This Method is only eligible for an unmeasured stratum, $u$, that shares the same organic amendment but differs in application rate, with at least one other stratum, $m$, that has been directly measured using Method 2. The measured baseline emission factor from the measured stratum is transformed to the unmeasured stratum using the ratio of scaling factors:

$EF_u = EF_m \times \frac{SF_{o,u}}{SF_{o,m}}$

(Equation 5)

Where:

• $EF_u$ represents the transformed emission factor for the unmeasured stratum, $u$, in kg CH₄/ha.
• $EF_m$ represents the measured baseline emission factor from Method 2 for the measured stratum, $m$, in kg CH₄/ha.
• $SF_{o,u}$ represents the organic amendment scaling factor evaluated for the application rate in stratum, $u$.
• $SF_{o,m}$ represents the organic amendment scaling factor evaluated for the application rate in stratum, $m$.

When a stratum, $u$, uses a blend of organic amendments, stratum $m$ must correspond with the most conservative classification as described in Section 7.2.1.

$CO_2e_{Project,RP}$ is the Project’s total GHG emissions within a Reporting Period, $RP$. This can be calculated as:

$CO_2e_{Project,RP}=CO_2e_{Rice,RP}+CO_2e_{Establishment,RP}+CO_2e_{Operations,RP}+CO_2e_{End-of-Life,RP}$

(Equation 6)

Where:

• $CO_2e_{Rice,RP}$ represents the total GHG emissions associated with either the residual CH₄ emissions or from increased N₂O that are part of the biogeochemical soil flux, represented for the Reporting Period, $RP$, in tonnes of CO₂e (see Section 8.4.1).
• $CO_2e_{Establishment,RP}$ represents the GHG emissions associated with project establishment, represented for the Reporting Period, $RP$, in tonnes of CO₂e (see Section 8.4.2).
• $CO_2e_{Operations,RP}$ represents the total GHG emissions associated with operational processes for a Reporting Period, $RP$, in tonnes of CO₂e (see Section 8.4.3).
• $CO_2e_{End-of-Life,RP}$ represents GHG emissions that occur after the Reporting Period and are allocated to a Reporting Period, $RP$, in tonnes of CO₂e (see Section 8.4.4).

$CO_2e_{Rice,RP}$ is presented as a distinct component from $CO_2e_{Operations,RP}$ because it represents the primary GHG fluxes that the project activity is designed to modify, i.e., residual methane from soil methanogenesis and the associated increase in nitrous oxide emissions resulting from the change in water regime. These emissions are mechanistically distinct from operational emissions (e.g., fuel consumption for pumping, land preparation, and monitoring activities) and are quantified using emission factor approaches specific to rice paddy biogeochemistry.

$CO_2e_{Rice,RP}$ is the total GHG emissions associated with a Reporting Period, $RP$. This can be calculated as:

$CO_2e_{Rice,RP}=CO_2e_{Rice,CH_4,RP}+CO_2e_{Rice,N_2O,RP}$

(Equation 7)

Where:

• $CO_2e_{Rice,CH_4,RP}$ represents the total residual CH₄ emissions from biogeochemical processes under project intervention, represented for the Reporting Period, $RP$, in tonnes of CO₂e (see Section 8.4.1.1).
• $CO_2e_{Rice,N_2O,RP}$ represents the total increased N₂O emissions due to changing water regime in the project intervention, represented for the Reporting Period, $RP$, in tonnes of CO₂e (see Section 8.4.1.2).

$CO_2e_{Rice,CH_4,RP}$ is calculated as:

$CO_2e_{Rice,CH_4,RP}=\sum\limits_g(EF_{P,g}\times A_g \times 10^{-3} \times GWP_{CH_4})$

(Equation 8)

Where:

• $EF_{P,g}$ represents the project emission factor for stratum $g$ in kg CH₄/ha determined using the same approach as the baseline emission factor (see Section 8.3.1).
• $A_g$ represents the area of project fields in stratum g, in hectares.
• $GWP_{CH_4}$ represents the 100-year global warming potential of CH₄ 27.9¹.
• $10^{-3}$ represent the conversion factor from kg CH₄ to tonnes CH₄.
• $g$ represents each individual stratum

Project activities that transition rice fields from continuous flooding to drained conditions result in increases in nitrous oxide (N₂O) emissions. Under continuous flooding, rice soils remain persistently anaerobic, suppressing nitrification and limiting N₂O production. When a field transitions to AWD, periodic drainage introduces aerobic conditions during dry-down periods. During these aerobic windows, ammonium (NH₄) in the soil is oxidized to nitrate (NO₃⁻) through nitrification. When the field is subsequently re-flooded, the resulting anaerobic conditions drive denitrification of this nitrate pool, producing N₂O as a by-product. This mechanism occurs regardless of whether nitrogen fertilizer application rates change, as it is driven by the shift in soil redox conditions.

Projects must calculate the difference in N₂O emissions between the baseline water regime and the project water regime and deduct the total from the net emission reductions.

N₂O emissions from the water regime change must be calculated as follows:

$CO_2e_{Rice,N_2O,RP}=\sum\limits_g(Q_{N,g,RP} \times A_g) \times EF_{AWD} \times 10^{-3} \times GWP_{N_2O}$

(Equation 9 )

Where:

• $Q_{N,g,RP}$ represents the total application rate of nitrogen inputs in the project scenario for field group g, in kg N per hectare over the Reporting Period, $RP$. Nitrogen inputs include synthetic fertilizers, organic amendments (e.g., manure, compost, green manure), and crop residue nitrogen returned to the soil.
• $A_g$ represents the area of project fields in field group g, in hectares.
• $EF_{AWD}$ represents the emission factor for N₂O increase due to the change in water regime, in kg N₂O per kg N-input (see Section 8.4.1.2.1) .
• $10^{-3}$ represent the conversion factor from kg N₂O to tonnes N₂O.
• $GWP_{N_2O}$ represents the 100-year global warming potential of N₂O. This term must be determined based on the most recent IPCC Assessment Report.

Country specific N₂O emission factors for rice cultivation under AWD are available for very few countries. Most Projects are therefore expected to apply IPCC default emission factors, which represent the best available data for contexts where country-specific data does not exist. Where peer-reviewed country- or region-specific data or direct field measurement capacity are available, Projects must apply the higher tier in accordance with the hierarchy set out below.

The emission factors $EF_{AWD}$ and $EF_{fert}$ must be selected according to the following tiered hierarchy. The Project Proponent must use the highest tier for which adequate data are available.

Tier 3: Direct Field Measurement

Where the Project has the capacity to conduct direct field measurement of N₂O fluxes using closed chamber methods with gas chromatograph–electron capture detector (GC-ECD) analysis, site-specific emission factors may be derived from these measurements. Tier 3 provides the highest accuracy and is the preferred approach where feasible.

Direct measurement requires sampling throughout the rice growing season at representative locations within each stratum, covering both flooded and drained periods. Measurement protocols must follow established guidelines for chamber-based N₂O flux measurement from rice paddy fields. N₂O fluxes are concentrated around hydrological transitions, with substantial pulses occurring during drainage and re-flooding events. Sampling protocols should be designed to capture these emission windows, for example, by increasing sampling frequency around drainage and re-flooding events. The measurement design, including sampling locations, frequency, and timing relative to hydrological transitions, must be documented in the PDD.

Use of Tier 3 is not mandatory. N₂O fluxes are episodic and highly variable in both space and time, requiring high sampling frequency and specialist laboratory equipment that may not be available in all project contexts.

Tier 2: Country-Specific or Regional Emission Factors

Where peer-reviewed, published emission factors specific to the project country or region are available, these must be used in preference to global defaults. Country-specific factors must be derived from field studies conducted under conditions comparable to the Project, including similar climate, soil type, water management regime, and nitrogen application practices.

The derivation of Tier 2 emission factors must follow the guidance provided in Chapter 11, Section 11.2.1.1³³ of Volume 4 of the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Tier 2 emission factors must be sourced from peer-reviewed scientific literature or from national greenhouse gas inventory reports submitted to the UNFCCC. The data sources, selection criteria, and statistical methods used to derive the emission factor must be documented in the Project Design Document.

Where adequate Tier 2 data are not available, the Project must use Tier 1 emission factors.

Tier 1: IPCC Default Emission Factors

Where neither Tier 3 nor Tier 2 data are available, the Project must use default emission factors derived from the IPCC 2019 Refinement to the 2006 Guidelines for National Greenhouse Gas Inventories (Table 11.1, Chapter 11, Volume 4)³³. Due to the limited availability of country-specific N₂O data for rice systems globally, most projects are expected to use Tier 1 (see Section 12.2 for reference values).

GHG emissions associated with project establishment should include all historic emissions incurred as a result of project establishment, including but not limited to the SSRs set out in Table 1. For rice methane reduction projects, this includes the manufacture, transport and installation of equipment and materials for water level tubes, bunds, drainage channels, and monitoring equipment.

Project establishment emissions occur from the point of project inception up until the first Reporting Period. Establishment emissions may be accounted for in the following ways, with the allocation method selected and justified by the Project Proponent:

• as a one-time deduction from the first verification, or
• amortized over the first Crediting Period (or less) as annual emissions.

GHG emissions associated with $CO_2e_{Operations,RP}$ must include all emissions associated with operational activities, including but not limited to the SSRs set out in Table 1 (Section 7.1).

$CO_2e_{Operations,RP}$ emissions occur over the Reporting Period for the deployment being credited and are applicable to the current deployment only. $CO_2e_{Operations,RP}$ emissions must be attributed to the Reporting Period in which they occur.

When the Project involves higher nitrogen application rates than the baseline, the additional nitrogen provides further substrate for nitrification and denitrification under drained conditions. Because this nitrogen enters a drained soil environment, it produces N₂O at the full emission rate applicable to drained rice fields.

Where the nitrogen application rate in the project scenario exceeds that of the baseline, additional N₂O emissions must be calculated as follows:

$CO_2e_{Fert,N_2O,RP}=\sum\limits_g(\Delta Q_{N,g} \times A_g)\times EF_{Fert}\times10^{-3}\times GWP_{N_2O}$

(Equation 10)

Where:

• $CO_2e_{Fert,N_2O,RP}$ represents the project emissions of N₂O from additional nitrogen application over the Reporting Period, $RP$, in tonnes CO₂e .
• $\Delta Q_{N,g}$ represents the incremental nitrogen application rate (project N-input minus baseline N-input) for field group $g$, where positive; zero otherwise, in kg N per hectare. This includes increases in nitrogen from synthetic fertilizers, organic amendments, or crop residue nitrogen
• $EF_{Fert}$ represents the emission factor for N₂O from additional nitrogen under drained conditions, in kg N₂O per kg N-input (see Section 8.4.1.2.1).
• $10^{-3}$ represent the conversion factor from kg N₂O to tonnes N₂O.
• $GWP_{N_2O}$ represents the 100-year global warming potential of N₂O. This term must be determined based on the most recent IPCC Assessment Report.

$CO_2e_{End-of-Life,RP}$ includes all emissions associated with activities that are anticipated to occur after the Reporting Period, but are directly or indirectly related to the Reporting Period. For example, this could include end-of-life emissions for project equipment (indirectly related to all deployments).

GHG emissions associated with $CO_2e_{End-of-Life,RP}$ may occur from the end of the Reporting Period onwards, and typically through to completion of project site deconstruction and any other end-of-life activities.

GHG emissions associated with activities that are indirectly related to all deployments may be allocated in the same ways as set out in $CO_2e_{Establishment,RP}$.

Project Proponents must use the most representative, accurate, and plausible data that is available at the time of assessment in the GHG Statement. Activity data used to inform GHG accounting may be primary data or secondary data. Project Proponents must strive to use primary data in GHG accounting, but secondary data may be used where primary data is either not available or not practical. More details on data requirements can be found in Section 3 of the GHG Accounting Module v1.1.

Project Proponents may exclude any SSRs included in Table 1 from the final net reduction quantification if these are demonstrated to be negligible. Negligible SSRs are those that fall below a Materiality threshold based on an environmental significance of less than 1% of net CO₂e reduction in any given Reporting Period. The sum of negligible SSRs must not be equal to or more than 1% of the net reduction.

To demonstrate this, Project Proponents may utilize an economic input-output (EEIO) approach as a preliminary screening test, estimating emissions based on project financial data (e.g., CAPEX data) combined with EEIO emission factors. If this screening demonstrates that emissions are below the Materiality threshold, emissions can be excluded or can be estimated using high-level estimations if included. See Section 5.0 of the Isometric GHG Accounting Module v1.1 for more details on the approach and example libraries.

Alternatively, where financial data is unavailable, Project Proponents may use other benchmarks to estimate emissions. For example, proponents may rely on physical benchmarks from industry-standard life cycle inventory databases based on activity-level parameters relevant to sectors similar to rice cultivation.

Ancillary activities, such as supplementary research and development activities and corporate administrative activities, that are associated with a Project but are not directly or indirectly related to the issuance of Credits can be excluded from the system boundary.

This section sets out specific requirements relating to the quantification of energy use as part of the GHG Statement. Emissions associated with energy usage result from the consumption of electricity or fuel for:

• Drainage and irrigation pumps
• Monitoring equipment operation
• Machinery used for land preparation.

Electricity

The following calculation approach must be used to estimate emissions from the project’s electricity consumption:

$CO_2e_{EC,PJ,RP}=EC_{grid,RP} \times EF_{grid,RP} \times (1 + f_{TDP-losses,RP}) + (EC_{generator,RP} \times EF_{generator,RP})*10^{-3}$

(Equation 11)

Where:

• $CO_2e_{EC,PJ,RP}$ represents total emissions from the project’s electricity consumption over the Reporting Period, $RP$, in tonnes CO₂e
• $EC_{grid,RP}$ represents the total electricity consumed from the grid over the Reporting Period, $RP$, in kWh
• $EF_{grid,RP}$ represents the emission intensity of the electricity grid over the Reporting Period, $RP$, in kg CO₂e/kWh
• $f_{TDP-losses,RP}$ represents the transmission and distribution grid losses factor
• $EC_{generator,RP}$ represents the total electricity consumed from a non-grid generator over the Reporting Period, $RP$, in kWh
• $EF_{generator,RP}$ represents the emission factor associated with the non-grid generator, in kg CO₂e/kWh
• $10^{-3}$ represents the conversion from kg to tonne.

Project Proponents may determine the emission intensity of the electricity grid, $EF_{grid,RP}$, using the following hierarchy:

1. Projects may use Combined Margin (CM) emission factors from a reputable source. The suitability and technical rigor of the selected CM factor and its source will be evaluated by Isometric on a case-by-case basis during project validation.
2. If appropriate CM factors are not available for the location of The Project, Project Proponent must apply one of the following default values for $EF_{grid,RP}$, based on the share of renewable and nuclear energy in the electric grid:

• 1.3 kg CO₂e/kWh if the share of renewables and nuclear is less or equal 33%;
• 0.87 kg CO₂e/kWh if the share of renewables and nuclear is between 33% and 67%;
• 0.44 kg CO₂e/kWh if the share of renewables and nuclear exceeds 67%.

If the generation source is a captive fossil fuel-fired power plant, Projects should make every attempt to gather information on the emission intensity of the technology generating the electricity. Where a specific emission intensity is not available, Projects must apply a default of 1.3 kg CO₂e/kWh.

Projects may determine the transmission and distribution grid losses factor, $f_{TD-losses,RP}$, using the following hierarchy:

1. Projects may use transmission and distribution grid losses factors from a reputable source;
2. If transmission and distribution grid losses factors are not available for the location of the Project, $f_{TD-losses,RP}$ is set at 25% for all Projects.

Fuels

Section 6 of the Energy Use Accounting Module v1.3 provides requirements on how fuel-related emissions must be calculated in a Project.

This section sets out specific requirements relating to the quantification of embodied emissions as part of the GHG Statement. Embodied emissions are those related to energy use or other emissions during the manufacture of equipment and materials used in a process.

Examples of project-specific materials and equipment that must be considered as part of the embodied emission calculation include, but are not limited to:

• water level observation tubes and AWD field tubes;
• drainage channel liners and bund construction materials;
• monitoring equipment (chambers, gas chromatographs, data loggers); and
• any materials used for repair, maintenance, or retrofits.

The GHG Accounting Module v1.1 sets out the approach to be followed to account for embodied emissions, including life cycle stages to be considered (Section 4.1), and data sources and emission factors (Section 3.3).

Section 4.2 of the GHG Accounting Module v1.1 provides requirements on how transportation-related emissions must be calculated in a Project.

Uncertainty deductions are applied to account for measurement and model uncertainties in the emission reduction calculation. Additionally, uncertainty deductions are used when regional emission factors are used for quantification. The applicable deduction depends on the emission factor determination method.

When estimating emissions using Method 1 (Section 8.3.1), a default uncertainty deduction of 15% must be applied to the emission reduction. This deduction reflects the inherent uncertainty in default emission and scaling factors that have not been validated by site-specific measurements.

Projects quantifying CH₄ emissions under Method 2 or Method 3 (Section 8.3.1) must compare the measured (or transformed) emission reduction distribution against the expected emission reduction derived from IPCC Tier 2 emission factors for the relevant country.

The Tier 2 expected baseline emission factor for each stratum is calculated using Equation 3 with the values provided in Appendix A. The Tier 2 expected emission reduction is the difference between the Tier 2 baseline and project emission factors for that stratum. The Tier 2 expected reduction includes an associated uncertainty range, derived from the minimum and maximum of the 95% confidence interval of the project intervention on-season water regime scaling factors (see Appendix A).

The 40^th percentile of the measured (or transformed) emission reduction distribution is compared against the Tier 2 expected reduction range to determine the credited emission reduction for the stratum:

• Where the 40^th percentile of the measured reduction distribution falls within the range of the Tier 2 expected reduction, measured reductions are consistent with country-level expectations. The credited emission reduction is the 40^th percentile of the measured reduction distribution.
• Where the 40^th percentile of the measured reduction distribution falls below the range of the Tier 2 expected reduction, measured reductions are unusually low relative to expectations but may reflect atypical local conditions. The credited emission reduction is the 40^th percentile of the measured reduction distribution.
• Where the 40^th percentile of the measured reduction distribution exceeds the upper bound of the Tier 2 expected reduction range, measured reductions are unusually high relative to country-level expectations and may indicate measurement error or unrepresentative site selection. The credited emission reduction is the greater of (a) the 16^th percentile of the measured reduction distribution, and (b) the upper bound of the Tier 2 expected reduction range.

This formulation ensures that the credited emission reduction is monotonically non-decreasing with respect to the measured reduction distribution, meaning a project whose measurements indicate larger reductions will never receive fewer Credits than an otherwise identical project with smaller measured reductions. The Tier 2 upper bound serves as a floor in the above-range case, reflecting that country-level evidence supports reductions at least that large, even where the measurement uncertainty penalty would otherwise reduce the credited quantity below the Tier 2 expectation.

Example Uncertainty Range Calculation

A Project in India is implementing multiple drainage (AWD) on fields that were previously continuously flooded in the baseline. The fields have a pre-season water regime that was non-flooded for < 180 days, apply 5 tons/ha of straw on-season as an organic amendment, and the cultivation period is 120 days. The uncertainty screening calculation would be as follows:

$SF_o = (1 + 5 × 1.00)^{0.59} = 2.878$

$EF_{Baseline} = 0.85 \times 1.00 \times 1.00 \times 2.878 \times 120 = 293.6\ \text{kg CH₄/ha}$

$EF_{ProjectLowerBound} = 0.85 \times 0.72 \times 1.00 \times 2.878 \times 120 = 211.4\ \text{kg CH₄/ha}$

$EF_{ProjectUpperBound} = 0.85 \times 0.41 \times 1.00 \times 2.878 \times 120 = 120.4\ \text{kg CH₄/ha}$

Table 2. Example expected range of methane reduction used for screening direct measurements to determine the uncertainty deductions.

This section establishes monitoring and documentation requirements necessary to ensure the accuracy, completeness, and credibility of rice methane reduction projects.

Requirements are grouped based the following:

• Rice Paddy Fields (project and reference)
• Farmer Training and Compliance Records
• Water Level Monitoring System
• GHG Quantification

Requirements are further organised into two categories:

• Validation requirements include evidence and documentation required at initial project registration.
• Verification requirements include ongoing evidence to be submitted for each Reporting Period.

Requirements are grounded in the following principles:

• Measurement Accuracy: CH₄ and N₂O quantities must be measured with sufficient precision to support credible emission reduction claims. Given the high GWP¹ of CH₄ (27.9) and N₂O (273), even small measurement errors can translate to significant over- or under-crediting.
• Field eligibility: All enrolled fields and farmers must be eligible, active, and appropriately documented.
• Drainage Verification: Water management changes must be independently verifiable through water level records and geotagged photographic evidence to confirm that drainage events occurred as claimed.

Validation Requirements

Projects must provide the geographic boundary of the project area, including GPS coordinates or geospatial boundary files for all project fields.

Projects must describe the baseline cultivation practices for each stratum, covering water regime, organic amendments, fertiliser type and rate, and rice varieties.

Acceptable evidence includes:

• a representative farmer survey;
• national or sub-national agricultural statistics; and/or
• regional extension-service records.

Projects must describe the planned project activity, including the target water management regime, the expected drainage schedule, and whether any other methane mitigation amendments are used.

Projects must confirm that the project fields are irrigated with controlled irrigation and drainage facilities.

For each enrolled field, Projects must demonstrate baseline eligibility evidence per Section 4.1.1, including:

• the project area is predominantly characterized by irrigated, flooded rice cultivation (fields classified as upland, rainfed, or deep water are not eligible);

• the baseline on-season water regime corresponds to one of the eligible conditions and is different from the proposed prohect activities (unless only implementing dry direct-seeded rice);

• the field was cultivated under an eligible baseline condition within the five years immediately preceding the initiation of the project activity;

• the number of seasons per year the field was cultivated for rice is consistent with the baseline period or with regional practices; and

• the project area has not been cleared of native ecosystems within the 10 years immediately preceding the project start date.

Where the project activity involves the introduction of a rice cultivar that has not previously been cultivated in the project region, the Project Proponent must demonstrate in the PDD that the newly introduced cultivar does not necessitate material changes to existing land management practices beyond those required by the eligible project activity itself (see Section 4.1.2).

Verification Requirements

For each Reporting Period, the following must be reported per field or per stratum:

• field identification (unique ID, GPS coordinates, area in hectares);
• rice variety planted and cultivation period (sowing/transplanting date, harvest date);
• water regime classification (baseline and project);
• organic amendment type and application rate, including synthetic N-fertiliser type and application rate if applicable; and
• dates of sowing and harvesting.

The Project Proponent must document, for each enrolled field, that the number of rice cultivation seasons per year maintained during the project period is the same as that practised during the baseline period.

• Where there is any change to the crop rotation or number of growing seasons per year under Project activities relative to the baseline, the Project Proponent must justify the change by factors other than Carbon Finance and demonstrate that the change remains consistent with common agricultural practices in the region (see Section 4.2).

The Project Proponent must stratify the project area per the criteria defined in Section 7.2. Each Reporting Period, project fields must be assigned to a stratum. Stratification may change between seasons to accommodate changes in organic amendment application. This section sets out the documentation requirements for stratification, the data sources used to assign values to each criterion, and the deliverables required for each stratum.

Validation Requirements

For each stratum, the PDD must include:

• a unique stratum identifier;

• the total area of the stratum;

• the values or designation assigned for each mandatory stratification criterion;

• where applicable, the values assigned for each conditional and optional criterion; and

• the data source and method used to determine each assigned value.

Data source requirements differ by criterion type:

• Dynamic criteria (water regime, organic amendments) must be determined from project-specific field management records or direct farmer reporting. Where project management records are not available for the baseline period, the Project Proponent must describe the method used to characterize baseline management practices and justify the representativeness of the data used.
• Static criteria (soil type, soil pH, SOC, soil texture, climate) may be determined from direct field measurement or from publicly available soil and climate databases. Acceptable databases include ISRIC SoilGrids³⁴, the Harmonized World Soil Database v2.0 (2023)³⁵, the World Reference Base for Soil Resources (2006)³⁴, national soil surveys, and the Köppen-Geiger climate maps²⁷. Where publicly available databases are used, the Project Proponent should validate the database values against field samples.

Stratum-level verification at each Reporting Period is addressed in Section 9.5.

When quantifying methane emissions with direct measurements, the following requirements apply:

Validation Requirements

Each measurement cluster must contain at least three reference fields for baseline measurements and at least three for project measurements.

• Reference fields should be located close to the project fields.

• Reference fields must share the same stratum classification (pre-season regime, organic amendments) as the project fields they represent.

• Baseline reference fields must maintain baseline conditions throughout the growing season. Project reference fields must implement the defined project activities.

Verification Requirements

At Verification, Projects must provide:

• Records confirming that reference fields maintained the intended water regime throughout the monitoring season.
• Water level records from reference fields at the same frequency as project fields.
• Confirmation that reference field management (fertiliser, organic amendments, rice variety) matched the corresponding stratum conditions.

Validation Requirements

For each enrolled field, Projects must provide one or more of the following forms of evidence:

• a land title, certificate of ownership, land use right certificate, or equivalent government-issued instrument;
• a written lease, tenancy, or sharecropping agreement that grants the participant the right to make cultivation management decisions;
• written confirmation from a recognised local authority, traditional governance body, cooperative, or farmer organisation attesting to the participant's right to cultivate the enrolled fields; or
• a signed farmer attestation of tenure (which may be recorded digitally), supported by at least one form of corroborating evidence such as: satellite imagery, historical cultivation, tax or agricultural subsidy records, input purchase or rice sales receipts, or a statement from an agricultural extension officer or neighbouring farmer.

Isometric may cross-reference official land registry records with satellite imagery and GIS data, where available.

Verification Requirements

Projects must confirm whether any changes in field ownership, tenancy, or management control occurred during the Reporting Period. Where a change occurred, projects must demonstrate for each affected field that the four conditions in Section 6.2.1.1 are met:

• the participation contract was transferred from the outgoing to the incoming project participant;
• the Project Proponent informed Isometric of the change in ownership before issuing Credits;
• the incoming project participant received training and technical support per Section 6.2.1.3; and
• implementation of the Project activity continued without interruption until the end of the Reporting Period.

Validation Requirements

For each participant at enrollment, Projects must provide:

• Identification of all fields under the participant's management control, with cross-references to GIS/KML boundary files.
• A signed participation agreement or contract between the farmer or land manager and the Project Proponent, specifying the terms of enrollment, rights and obligations, and the duration of participation.

Verification Requirements

Projects must provide an updated participant register for each Reporting Period, identifying additions and removals relative to the prior period.

• For new participants, the validation documentation above must be provided.
• For removed participants, Projects must confirm that the associated fields are excluded from emission reduction calculations.

Validation Requirements

The Project Proponent must describe the training program for farmers participating in the project, covering AWD principles and drainage scheduling, water level observation procedures, fertilizer management, and record-keeping obligations.

Training must be documented through attendance registers, training materials, and photographic evidence.

Projects must describe the benefit-sharing mechanism with enrolled farmers. This should include:

• the basis for farmer compensation (e.g., per-hectare payment, per-credit share, in-kind support, or a combination thereof); and
• how benefits are distributed.

Verification Requirements

Training records must be updated each Reporting Period with evidence of training any newly enrolled farmers.

As part of ensuring compliance and for quantification of emissions reduction, farmers must submit logbooks or digital records documenting:

• irrigation and drainage events;
• fertilizer/organic amendment application dates, types, and rates; and
• dates of sowing and harvesting.

Water level monitoring is required for fields implementing drainage-based project activities (see Section 4.2.1). This section sets out the validation and verification deliverables for monitoring methods, recording procedures, and field records. The eligibility threshold (15 cm below the soil surface, or -20 kPa for fields monitored by digital sensor measuring soil water potential) and the exemption mechanism (national agronomist approval) are specified in Section 4.2.1.

Validation Requirements

The Project Proponent must describe the water level observation method, including placement, observation frequency, and data-capture format. Acceptable methods include: perforated observation tubes (field water tubes) installed at designated monitoring points within each field, or automated water level sensors with data logging capability.

• The location of water tubes or sensors should be at least 1 m away from the bund and in a location that is representative of the soil level of the field (not within a depression or elevated patch)⁷.

Verification Requirements

Projects must submit water level records for each monitored field or monitoring point, including:

• water level measurements (cm relative to soil surface, or kPa where soil water potential is measured);
• height of re-flooding (if applicable); and
• observer name and affiliation.

At least 5% of fields must have a geotagged photo of the water level measurement at the point of re-flooding for each drainage event.

• Projects must also submit precipitation records for the project area during the Reporting Period (from local weather stations or reliable meteorological services).

Validation Requirements

Projects must describe the intended quantification method per Section 8.3.1.

When quantifying methane emissions with direct measurements, Projects must describe the closed-chamber measurement protocol, which must comply with the following minimum standards:

• Chambers must be deployed in each of the three reference fields and project fields per measured stratum.

• Strata over 10,000 ha should have at least one measurement cluster and strata exceeding 25,000 hectares should have one additional measurement cluster for each additional 25,000 ha (or fraction thereof). Projects must document the rationale for cluster placement in the PDD.

• Chamber design and installation must minimize disturbance to the soil and water surface.

• Gas sampling must be conducted at a minimum every two weeks throughout the entire growing season (from transplanting/sowing to harvest). It is recommended to sample weekly during times of larger expected fluxes.

• At each sampling event, a minimum of three gas samples must be collected per chamber at regular intervals during a 20–30 minute enclosure period (e.g., at 0, 10, 20 and 30 minutes).

• Measurements should be taken at matched time points between 08:00 and 12:00 across the reference fields and treatment areas to be comparable with most published estimates

Gas analysis must use methods capable of detecting CH₄ and N₂O (where applicable) at concentrations relevant to field flux measurements, with demonstrated precision and accuracy traceable to certified reference standards. Suitable methods include, but are not limited to, gas chromatography (e.g., FID for CH₄, ECD for N₂O) and laser-based absorption spectroscopy (e.g., CRDS, OA-ICOS).

• The laboratory must hold ISO 17025 accreditation or demonstrate equivalent quality assurance as approved by Isometric. Method blanks, laboratory control samples, and matrix spike samples must be analyzed with each batch.

Verification Requirements

When applicable, field measurements must be conducted at least every two weeks to sufficiently capture changes over a season. For each measurement campaign, the following must be reported:

• chamber placement map;
• gas concentration data for each time point (ppm);
• calculated flux rates (mg CH₄/m²/hr) and seasonal cumulative emissions (kg CH₄/ha/season);
• the time of day measurement was taken;
• temperature, and water depth at time of measurement;
• laboratory analysis reports with QA/QC documentation.

Emission factors derived from field measurements must be accompanied by uncertainty estimates (standard error, 95% confidence intervals).

To ensure consistency and accuracy, the following reconciliation checks must be performed at each verification:

• Total project area claimed must reconcile with the sum of individual field areas, verified against geospatial records.
• The participant register must reconcile with the number of fields claimed, land tenure evidence, and verified against GIS/KML boundary files.
• Training records must be consistent with the participant register (i.e. all enrolled farmers accounted for).
• The number and timing of drainage events claimed per field must be consistent with water level monitoring records.
• Emission factors applied must correspond to the correct stratum classification for each field.
• Fertilizer and organic amendment data must be consistent across farmer records and stratum classification.

Discrepancies exceeding 5% in area or emission factor assignment must require corrective action and justification before credits can be issued.

Isometric would like to thank the following external contributors to this protocol:

• Katie Kaku, Ph.D

All emission factors and scaling factors are those developed by Wang et al. (2018)³⁰ using 1,089 field measurements and used in the IPCC 2019 Refinement²⁵.

Project proponents may substitute alternative emission factors or scaling factors where these are derived from peer-reviewed (or equally rigorous) publications, provided they are applicable to the project's region, climate, and management conditions, and approved in consultation with Isometric.

Baseline emission factors (EF) for continuously flooded fields with no organic amendment and a pre-season water regime that was non-flooded for < 180 days before cultivation for use in Equation 3. EFs and confidence interval are reported in kg CH₄ ha⁻¹ day⁻¹.

Table A1. Country-Specific Baseline Emission Factors

For countries not listed, the global EF of 1.19 kg CH₄ ha⁻¹ d⁻¹ may be used.

Scaling factors are relative to continuously flooded conditions (= 1.00). Multiply the baseline EF by $SF_w$ in Equation 3 to adjust for the water regime during the crop growing season. The upper and lower CI values are used in for determining the expected range as part of the Tier 2 screening for uncertainty (see Section 8.6.2).

Table A2. Scaling Factors for Water Regime During Growing Season ($SF_w$)

Mean CH₄ fluxes and relative emission factors by pre-season water regime. Relative flux is expressed in relation to < 180 of non-flooded conditions before cultivation (= 1.00). Figure A1 provides a visual description of the eligble categories of pre-season water regimes.

Figure A1. Diagram of pre-season water conditions adapted from Table 5.13 in the 2019 IPCC Refinement²⁵.

Table A4. Pre-Season Water Regime Conversion Factors (SF_p)

*Detailed definitions of pre-season water regime conditions may be found in Wang et al. (2018)³⁰.

Mean CH₄ fluxes and relative emission factors by organic amendment type. Relative flux is expressed relative to straw applied on-season (= 1.00). The upper and lower CI values are used in for determining the expected range as part of the Tier 2 screening for uncertainty (see Section 8.6.2).

Table A3. Relative Emission Factors by Organic Amendment Type

The 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories provides a Tier 1 methodology for estimating nitrous oxide (N₂O) emissions from managed cropland soils, relying on default emission factors applied to various nitrogen inputs.

The emission factor for the water regime change (EF_AWD) is derived from the difference between the IPCC disaggregated EF_1FR values for continuously flooded rice fields and rice fields with single or multiple drainage.

This factor must be applied to the total nitrogen input in the project scenario for all fields switching from continuous flooding to AWD, regardless of whether nitrogen application rates change.

Where the project scenario involves nitrogen application rates exceeding those of the baseline, the emission factor for the additional nitrogen ($EF_{Fert}$) is the full IPCC EF_1FR for drained rice fields, converted from N₂O-N to N₂O.

EF_Fert is higher than EF_AWD because it represents the full N₂O emission rate under drained conditions for nitrogen that was not present in the baseline scenario, rather than the incremental difference between water regimes. This factor must be applied only to the incremental nitrogen (project N-input minus baseline N-input, where positive).

This Protocol was developed based on the current state of the art, publicly available science regarding rice methane reduction. This Protocol will be updated in future versions as the science underlying alternative rice agricultural techniques evolves and the overall body of knowledge and data across all processes is increased.

The following topics present future areas for expansion of this Protocol:

• Process-based models of methane emissions, including the use of machine learning
• Use of remote sensing for quantification and verification of project activities
• More precise estimations of nitrous oxide emissions
• Additional eligible cultivation techniques such as furrow-irrigated rice
• Improved stratification guidance

This Protocol will be reviewed when there is an update to published scientific literature, government policies, or legal requirements that would affect net emissions quantification or the monitoring guidelines outlined in this Protocol, or at a minimum of every 2 years.

1. IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report (AR6). ↩ ↩² ↩³ ↩⁴

2. Saunois, M. et al. (2020). The Global Methane Budget 2000–2017. Earth System Science Data, 12, 1561–1623. https://doi.org/10.5194/essd-12-1561-2020 ↩

3. Jiang, Y., Carrijo, D., Huang, S., Chen, J., Balaine, N., Zhang, W., van Groenigen, K.J., & Linquist, B. (2019). Water management to mitigate the global warming potential of rice systems: A global meta-analysis. Field Crops Research, 234, 47–54. https://doi.org/10.1016/j.fcr.2019.02.010 ↩

4. Qian, H., Zhu, X., Huang, S., Linquist, B., Kuzyakov, Y., Wassmann, R., ... & Jiang, Y. (2023). Greenhouse gas emissions and mitigation in rice agriculture. Nature Reviews Earth & Environment, 4(10), 716-732. https://doi.org/10.1038/s43017-023-00482-1 ↩

5. Carrijo, D. R., Lundy, M. E., & Linquist, B. A. (2017). Rice yields and water use under alternate wetting and drying irrigation: A meta-analysis. Field Crops Research, 203, 173-180. https://doi.org/10.1016/j.fcr.2016.12.002 ↩

6. Bouman, B.A.M., Humphreys, E., Tuong, T.P., & Barker, R. (2007). Rice and Water. Advances in Agronomy, 92, 187–237. https://doi.org/10.1016/S0065-2113(04)92004-4 ↩ ↩²

7. Bouman, B.A.M., Lampayan, R. M., and Tuong, T. P. (2007). Water Management in Irrigated Rice: Coping with Water Scarcity. International Rice Research Institute, Los Baños, Philippines. ↩ ↩²

8. Lampayan, R. M., Rejesus, R. M., Singleton, G. R., & Bouman, B. A. (2015). Adoption and economics of alternate wetting and drying water management for irrigated lowland rice. Field Crops Research, 170, 95-108. https://doi.org/10.1016/j.fcr.2014.10.013 ↩

9. Prithwiraj, D. (2017). Smart water management in rice by IRRI’s cost effective pani-pipe method for sustainable and climate smart rice development-A short communication. International Journal of Agriculture Sciences, ISSN, 0975-3710. ↩

10. Carrijo, D. R., Lundy, M. E., & Linquist, B. A. (2017). Rice yields and water use under alternate wetting and drying irrigation: A meta-analysis. Field Crops Research, 203, 173-180. https://doi.org/10.1016/j.fcr.2016.12.002 ↩ ↩² ↩³

11. Singh, C., Tiwari, S., Boudh, S., & Singh, J. S. (2017). Biochar application in management of paddy crop production and methane mitigation. In Agro-Environmental Sustainability: Volume 2: Managing Environmental Pollution (pp. 123-145). Springer International Publishing. ↩

12. He, H., Li, D., Wu, Z., Wu, Z., Hu, Z., & Yang, S. (2024). Assessment of the straw and biochar application on greenhouse gas emissions and yield in paddy fields under intermittent and controlled irrigation patterns. Agriculture, Ecosystems & Environment, 359, 108745. https://doi.org/10.1016/j.agee.2023.108745 ↩

13. Ume, C., Kalu, U. F., Ezeibe, A. B. C., Ume, C. S., Ugwuoke, C. O., Onah, O., & Joseph, D. C. (2025). Critical perspectives on the use of methanotrophs in rice farming: Advances in microbial climate mitigation. Cleaner Food Systems, 2, 100005. https://doi.org/10.1016/j.clfs.2025.100005 ↩

14. Ishfaq, M., Farooq, M., Zulfiqar, U., Hussain, S., Akbar, N., Nawaz, A., & Anjum, S. A. (2020). Alternate wetting and drying: A water-saving and ecofriendly rice production system. Agricultural Water Management, 241, 106363. https://doi.org/10.1016/j.agwat.2020.106363 ↩

15. World Resources Institute, LimnoTech, Bluerisk, Bonneville Environmental Foundation. 2025. “Volumetric Water Benefit Accounting 2.0: Guidance for implementing, evaluating, and claiming volumetric water benefits of water stewardship projects.” Guidebook. Washington, DC: World Resources Institute. Available online at: https://doi.org/10.46830/wrigb.23.00112. ↩

16. Cooley, D., and L. Olander. 2011 Stacking Ecosystem Services Payments: Risk and Solutions. NI WP 11-04. Durham, NC: Nicholas Institute for Environmental Policy Solutions, Duke University. ↩

17. Robertson, M., BenDor, T. K., Lave, R., Riggsbee, A., Ruhl, J. B., & Doyle, M. (2014). Stacking ecosystem services. Frontiers in Ecology and the Environment, 12(3), 186-193. https://doi.org/10.1890/110292 ↩

18. Rafy, A.U., Mohammed, M., Bohlen, J.S., & Banongwie, R. (2025). Long-term Effects of Water-Saving Irrigation on Soil Organic Carbon, Microbial Biomass, and Soil Structure in Paddy Fields: A Meta-Analysis. European Journal of Ecology, Biology and Agriculture, 2(6), 60-68. https://doi.org/10.59324/ejeba.2025.2(6).07 ↩

19. Samset, B. H., Wilcox, L. J., Lund, M. T., Iles, C., Stjern, C. W., & Nordling, K. (2023,). Near-term precipitation change highly sensitive to black carbon emissions. In EGU General Assembly Conference Abstracts (pp. EGU-3152). 10.5194/egusphere-egu23-3152 ↩ ↩² ↩³

20. Bond, T. C., Doherty, S. J., Fahey, D. W., Forster, P. M., Berntsen, T., DeAngelo, B. J., ... & Zender, C. S. (2013). Bounding the role of black carbon in the climate system: A scientific assessment. Journal of Geophysical Research: Atmospheres, 118(11), 5380-5552. https://doi.org/10.1002/jgrd.50171 ↩ ↩²

21. IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp, doi:10.1017/CBO9781107415324 ↩

22. Denjean, C., Brito, J., Libois, Q., Mallet, M., Bourrianne, T., Burnet, F., Dupuy, R., Flamant, C., & Knippertz, P. (2020). Unexpected biomass burning aerosol absorption enhancement explained by black carbon mixing state. Geophysical Research Letters, 47, e2020GL089055. https://doi.org/10.1029/2020GL089055 ↩

23. Doherty, S. J., Saide, P. E., Zuidema, P., Shinozuka, Y., Ferrada, G. A., Gordon, H., Mallet, M., Meyer, K., Painemal, D., Howell, S.G., Freitag, S., Dobracki, A., Podolske, J.R., Burton, S.P., Ferrare, R.A., Howes, C., Nabat, P., Carmichael, G.R., da Silva, A., Pistone, K., Chang, I., Gao, L., Wood, R., & Redemann, J. (2021). Modeled and observed properties related to the direct aerosol radiative effect of biomass burning aerosol over the Southeast Atlantic. Atmospheric Chemistry and Physics Discussions, 2021, 1-88. https://doi.org/10.5194/acp-22-1-2022 ↩

24. Giuffrida, E., Johnson, K., Tatro, T., Zuidema, P., & Gordon, H. (2025). Biomass burning aerosol radiative effects in the Southeast Atlantic depend strongly on meteorological forcing method. Atmospheric Chemistry and Physics, 25(21), 1487914879-1487914907. https://doi.org/10.5194/acp-25-14879-2025 ↩

25. IPCC, 2019: Chapter 5: Cropland. In: 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Vol. 4, Agriculture, Forestry and Other Land Use [Calvo Buendia, E., Tanabe, K., Kranjc, A., Jamsranjav, B., Brown, S., et al. (eds.)]. ↩ ↩² ↩³ ↩⁴ ↩⁵

26. Xiao, D., Ye, C., Ma, H., Xu, Y., Tao, Y., Zhu, J., Liao, W., Chen, S., Chu, G., Liu, Y., Yu, K., Xu, C., & Wang, D. (2025). Soil texture drives rice methane emissions at tillering stage via carbon fractions, nutrients and microbial abundance. Journal of Integrative Agriculture. https://doi.org/10.1016/j.jia.2025.12.049 ↩

27. Beck, H. E., Zimmermann, N. E., McVicar, T. R., Vergopolan, N., Berg, A., & Wood, E. F. (2018). Present and future Köppen-Geiger climate classification maps at 1-km resolution. Scientific Data, 5(1), 180214. https://doi.org/10.1038/sdata.2018.214 ↩ ↩²

28. Yu Jiang, Daniela Carrijo, Shan Huang, Ji Chen, Nimlesh Balaine, Weijian Zhang, Kees Jan van Groenigen, Bruce Linquist, Water management to mitigate the global warming potential of rice systems: A global meta-analysis, Field Crops Research, Volume 234, 2019, Pages 47-54, ISSN 0378-4290. https://doi.org/10.1016/j.fcr.2019.02.010. ↩

29. Bo, Y., Wang, X., van Groenigen, K.J. et al. Improved alternate wetting and drying irrigation increases global water productivity. Nature Food 5, 1005–1013 (2024). https://doi.org/10.1038/s43016-024-01081-z ↩

30. Wang, J., Akiyama, H., Yagi, K., & Yan, X. (2018). Controlling variables and emission factors of methane from global rice fields. Atmospheric Chemistry and Physics, 18(14), 10419-10431. https://doi.org/10.5194/acp-18-10419-2018 ↩ ↩² ↩³

31. Neue, H. U., Wassmann, R., Kludze, H. K., Bujun, W., & Lantin, R. S. (1997). Factors and processes controlling methane emissions from rice fields. Nutrient Cycling in Agroecosystems, 49(1), 111-117. https://doi.org/10.1023/A:1009714526204 ↩

32. Sander, B. O., & Wassmann, R. (2014). Common practices for manual greenhouse gas sampling in rice production: a literature study on sampling modalities of the closed chamber method. Greenhouse Gas Measurement and Management, 4(1), 1-13. https://doi.org/10.1080/20430779.2014.892807 ↩

33. IPCC, 2019: Chapter 11: N₂O Emissions from Managed Soils, and Emissions from Lime and Urea Application. In: 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories [Calvo Buendia, E., Tanabe, K., Kranjc, A., Jamsranjav, B., Brown, S., Meijide, A., et al. (eds.)]. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷

34. IUSS Working Group WRB (2006), World Reference Base for Soil Resources 2006. A Framework for International Classification, Correlation and Communication, 2nd ed., World Soil Resources Reports No. 103, FAO, Rome. Available at https://soilgrids.org/ ↩ ↩²

35. FAO & IIASA. 2023. Harmonized World Soil Database Version 2.0. Rome and Laxenburg. https://doi.org/10.4060/cc3823en ↩