In general, it is good practice to document and archive all information required to produce the national inventory estimates. For Tier 1, inventory compilers should document activity data trends and uncertainties for croplands. Key activities include land-use change, use of mineral fertilizers, agroforestry practices, organic amendments, tillage management, cropping rotations, residue management (including burning), irrigation practices, extent of mixed cropping systems, water management in rice systems, and land-use change.
It is good practice to archive actual databases, such as agricultural census data, and procedures used to process the data (e.g., statistical programs); definitions used to categorize or aggregate activity data; and procedures used to stratify activity data by climate regions and soil types (for Tier 1 and Tier 2). The worksheets or inventory software should be archived with input/output files that were generated to produce the results.
In cases where activity data are not available directly from databases or multiple data sets were combined, the information, assumptions and procedures that were used to derive the activity data should be described. This documentation should include the frequency of data collection and estimation, and uncertainty. Use of expert knowledge should be documented and correspondences archived.
It is good practice to document and explain trends in biomass and soil C stocks, as well as biomass burning in terms of the land-use and management activity. Changes in biomass stocks should be linked directly to land use or changes in agroforestry practices, while trends in soil C stocks may be due to land use or shifts in key management activities, as described above. Biomass burning emissions from residues will depend on the extent to which burning is used to prepare fields for planting. Significant fluctuations in emissions between years should be explained.
Countries need to include documentation on completeness of their inventory, issues related to time series consistency or lack thereof, and a summary of Quality Assurance/Quality Control measures and results.
In addition to the Tier 1 considerations, inventory compilers should document the underlying basis for country-specific C stock change factors, reference soil C stocks, residue estimated (fuel loads), combustion and emission factors for biomass burning, management system classifications, climate regions and/or soil types. Furthermore, it is good practice to archive metadata and data sources for information used to estimate country-specific values.
Reporting documentation should include the country-specific factors (i.e., means and uncertainties). It is good practice to include a discussion in the inventory report about differences between country-specific factors and Tier 1 defaults as well as Tier 2 factors from regions with similar circumstances as the reporting country. If different emission factors, parameters and methods are used for different years, the reasons for these changes should be explained and documented. In addition, inventory agencies should describe country-specific classifications of management, climate and/or soil types, and it is recommended that improvements in the inventory methods based on the new classifications be documented. For example, tillage management practices may be subdivided into additional categories beyond the Tier 1 classes (i.e., reduced, no-till and full tillage), but further subdivisions will only improve inventory estimates if the stock change or emission factors differ significantly among the new categories.
When discussing trends in emissions and removals, a distinction should be made between changes in activity levels and changes in methods from year to year, and the reasons for these changes need to be documented.
Tier 3 inventory will need similar documentation about activity data and emission/removal trends as lower tier approaches, but additional documentation should be included to explain the underlying basis and framework of the country-specific estimation system. With measurement-based inventories, it is good practice to document the sampling design, laboratory procedures and data analysis techniques. Measurement data should be archived, along with results from data analyses. For Tier 3 approaches that use models, it is good practice to document the model version and provide a model description, as well as permanently archive copies of all model input files, source code and executable programs.
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