Identification of key categories

The background discussion on the approach and methods for key category analysis are given in Volume 1 Chapter 4 (Methodological Choice and Identification of Key Categories). This chapter describes the approach to key category analysis for AFOLU. A key source/sink category is defined in Volume 1 Chapter 4 as one that is prioritised within the national inventory system because its estimate has a significant influence on a country's total inventory of greenhouse gases in terms of the absolute level, the trend, or the uncertainty in emissions and removals. Key category analysis helps a country to achieve the most reliable inventory given the resources available. Key category analysis is required to identify the following:

• which land-use and management activities are significant;

• which land-use or livestock (sub)category is significant;

• which CO2 emissions or removals by sinks from various carbon pools are significant;

• which non-CO2 gases and from what categories are significant; and

• which tier is required for reporting.

4 No default methodology exists for estimation of CH4 removals in aerobic soils because of limited studies addressing land-use and management impacts on methane oxidation. Countries that wish to estimate and report CH4 removals should develop, validate and document an appropriate national methodology for estimating CH4 removals, including analysis of uncertainty. It is good practice for countries reporting CH4 removals to also ensure symmetry by including all emissions of CH4 on lands were CH4 removals are reported.

Box 1.1

Framework of tier structure for AFOLU methods

Tier 1 methods are designed to be the simplest to use, for which equations and default parameter values (e.g., emission and stock change factors) are provided in this volume. Country-specific activity data are needed, but for Tier 1 there are often globally available sources of activity data estimates (e.g., deforestation rates, agricultural production statistics, global land cover maps, fertilizer use, livestock population data, etc.), although these data are usually spatially coarse.

Tier 2 can use the same methodological approach as Tier 1 but applies emission and stock change factors that are based on country- or region-specific data, for the most important land-use or livestock categories. Country-defined emission factors are more appropriate for the climatic regions, land-use systems and livestock categories in that country. Higher temporal and spatial resolution and more disaggregated activity data are typically used in Tier 2 to correspond with country-defined coefficients for specific regions and specialized land-use or livestock categories.

At Tier 3, higher order methods are used, including models and inventory measurement systems tailored to address national circumstances, repeated over time, and driven by high-resolution activity data and disaggregated at sub-national level. These higher order methods provide estimates of greater certainty than lower tiers. Such systems may include comprehensive field sampling repeated at regular time intervals and/or GIS-based systems of age, class/production data, soils data, and land-use and management activity data, integrating several types of monitoring. Pieces of land where a land-use change occurs can usually be tracked over time, at least statistically. In most cases these systems have a climate dependency, and thus provide source estimates with interannual variability. Detailed disaggregation of livestock population according to animal type, age, body weight etc., can be used. Models should undergo quality checks, audits, and validations and be thoroughly documented.

The following chapters provide methodologies covering a broad array of source/sink categories in AFOLU. Not all categories are expected to be key and hence simple default methods (Tier 1) are provided to enable a complete inventory of AFOLU without requiring large investments of resources in relatively minor categories.

The analysis should be performed at the level of IPCC source or sink categories as suggested in Table 4.1 of Volume 1. The analysis should be performed using CO2-equivalent emissions estimated using the global warming potentials for each gas. The key category evaluation should be performed for each of these gases separately because the methods, emission factors and related uncertainties differ for each gas, pool and category. Source categories that use the same emission factors based on common assumptions should be aggregated before analysis. For each key category, the inventory agency should determine if certain sub-categories represent a significant share of the emissions. In the case of CH4 emissions from enteric fermentation in domestic livestock, for example, emissions from particular species (e.g., cattle, buffalo or sheep) are likely to represent the major share of emissions (GPG2000, Chapter 7). In the case of CO2 emissions/removals, a certain land category (e.g., Land Converted to Forest Land) and further a certain carbon pool (e.g., above-ground biomass) may contribute to a dominant share of net CO2 emissions/removals.

The level of aggregation or disaggregation of different land-use (see Chapter 3) and livestock categories (see Chapter 10) depends on the share of a given land-use or livestock system within a country's greenhouse gas inventory and on the level of resources available in the country for inventory activities. Disaggregation of land and livestock categories helps in reducing the uncertainty; however it increases the cost of the inventory process. Thus, there is a need for balance between level of disaggregation and the resources available for inventory.

Once identified, the key sources are used for methodological choice via decision trees as shown below. Those for the AFOLU include:

• decision tree for identification of appropriate tier level for land remaining in the same land-use category (Figure 1.2), for e.g., Forest Land Remaining Forest Land;

• decision tree for identification of appropriate tier level for land converted to another land-use category (Figure 1.3), for e.g., other Land Converted to Forest Land; and

• decision trees for enteric fermentation and manure management which are provided in the relevant sectoral chapter (see Chapter 10).

Figure 1.2 Decision tree for identification of appropriate tier level for land remaining in the same land-use category, using Forest Land Remaining Forest Land as an example.

Repeat for each land-use category:

- FF-Forest land remaining Forest land

- CC-Cropland remaining Cropland

- GG-Grassland remaining Grassland

- WW-Wetland remaining Wetlands

- SS-Settlement remaining Settlements

- OO-Other land remaining Other land

Repeat for each gas

Report "Not

1 w

Occurring".

Figure 1.2 Decision tree for identification of appropriate tier level for land remaining in the same land-use category, using Forest Land Remaining Forest Land as an example.

Note:

1: The use of 20 years, as a threshold, is consistent with the defaults contained in IPCC Guidelines. Countries may use different periods where appropriate to national circumstances (see Chapter 2).

2: See Volume 1 Chapter 4, "Methodological Choice and Identification of Key Categories" (noting section 4.1.2 on limited resources), for discussion of key categories and use of decision trees. 3: See Table 1.2 for the characterisation of subcategories.

4: A subcategory is significant if it accounts for 25-30% of emissions/removals for the overall category. 5: See Box 1.1 for definition of Tier levels.

6: Data availability refers to both data needed for developing country-specific emission factors and data on land use and management practices (activity data).

* If a country reports harvested wood products (HWP) as a separate pool, it should be treated as a subcategory.

Figure 1.3 Decision tree for identification of appropriate Tier level for land converted to another land-use category, using Land Converted to Forest Land as an example.

Figure 1.3 Decision tree for identification of appropriate Tier level for land converted to another land-use category, using Land Converted to Forest Land as an example.

Note:

1: The use of 20 years, as a threshold, is consistent with the defaults contained in IPCC Guidelines. Countries may use different periods where appropriate to national circumstances (see Chapter 2).

2: See Volume 1 Chapter 4, "Methodological Choice and Identification of Key Categories" (noting section 4.1.2 on limited resources), for discussion of key categories and use of decision trees. 3: See Table 1.2 for the characterisation of subcategories.

4: A subcategory is significant if it accounts for 25-30% of emissions/removals for the overall category. 5: See Box 1. 1 for definition of Tier levels.

6: Data availability refers to both data needed for developing country-specific emission factors and data on land use and management practices (activity data)

* If a country reports harvested wood products (HWP) as a separate pool, it should be treated as a subcategory.

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