Assessing different IPCC Tier Approaches for estimating Methane Emissions in Vietnamese Rice Agriculture

The IPCC provides three distinct protocols (Tier 1-3) that can be used for reporting on greenhouse gas (GHG) emissions under the UNFCCC. While Tier 1 and 2 use relatively straightforward methods based on global and region-specific emission factors, Tier 3 is more complex and uses process models for emission estimation. Although Tier 3 is considered to have higher accuracy potential, its complexity requires expert knowledge and extensive input data, which is often not available, hindering widespread adoption.

This study critically evaluates all three Tier approaches for CH₄ emissions from rice production in Vietnam, using the ecosystem process model LandscapeDNDC for the Tier 3 approach. As a first step, we evaluate all three approaches based on a comprehensive dataset covering 73 cropping seasons from 36 sites across Vietnam. On this basis, we show the extent to which Tier 3 performs better when considering commonly available information, and which information is most important to outperform simpler methods. As a second step, we present national CH₄ emission inventories for each approach and show under which circumstances the approaches differ the most. We also present a web-based tool that improves the accessibility of Tier 3 applications for users who are not familiar with the application of a particular complex process model.

Our findings aim to provide valuable insights into the effectiveness of UNFCCC reporting approaches, particularly the under-researched Tier 3.