Carbon Inventory Methods for National Greenhouse Gas Inventory

All countries that are signatories to the United Nations Framework Convention on Climate Change (UNFCCC) are expected to prepare national greenhouse gas (GHG) inventories, annually in the case of Annex-1 (industrialized) countries and periodically - once in 3-5 years - in the case of Non-annex-1 (largely the developing) countries. A national GHG inventory requires estimation of GHG emissions by source and removals by sinks from all sectors in a country for a given year or period. All the member countries of the UNFCCC are expected to use the Revised 1996 Guidelines for National GHG Inventory for Land Use Change and Forest Sector (LUCF). The use of Revised 1996 Guidelines for GHG inventory is set out in various decisions and conclusions of the UNFCCC (IPCC 2002). The Revised 1996 IPCC Guidelines stipulate the following sectors for national GHG inventory:

1. Energy

2. Industrial Processes

3. Agriculture

4. Land-Use Change and Forestry (LUCF)

5. Waste

Further, IPCC prepared Good Practice Guidance (IPCC 2003) for Land-Use Land Use Change and Forest Sector (LULUCF) to reduce uncertainty in the inventory estimates. IPCC (2000) defines inventories consistent with good practice as those which contain neither overestimates nor underestimates, so far as can be judged, and in which uncertainties are reduced so far as is practicable. The Good Practice Guidance (IPCC 2003) provides guidelines for carbon inventories for afforestation, reforestation and avoided deforestation projects in addition to those for land-use categories such as forest land, cropland and grassland.

Countries preparing the GHG inventory for submission to the UNFCCC use The Revised 1996 IPCC Guidelines along with the Good Practice Guidance. However, IPCC has further prepared IPCC 2006 GHG Inventory Guidelines based on the experience gained in using The Revised 1996 IPCC Guidelines and improvements in scientific methods for the following sectors:

• Industrial Processes and Products Use

• Agriculture, Forests and Other Land-uses (AFOLU)

Each sector comprises categories and subcategories. Guidelines for the AFOLU sector of IPCC 2006 Guideline attempts to overcome many of the limitations of the earlier IPCC 1996 Guidelines by providing the following:

• Good practice guidance for all GHGs for all land-use categories and carbon pools

• Tiers, which represent differing levels of complexity in methods

• Key category analysis to identify categories that have significant influence on the total inventory for the country

• Default data (improved default data to enable use of new the inventory guidelines)

• Worksheets to calculate emissions and removals

• Uncertainty estimation methods and guidance on reducing uncertainty

• Quality assurance (QA) and quality control (QC) to check and review the estimates for ensuring quality of the estimates

• Reporting framework to report the national inventory estimates

The inventory guideline also provides guidance on ensuring quality at all stages of inventory compilation and aims at enhancing transparency, completeness, consistency, comparability and accuracy. The IPCC 2006 Inventory Guidelines are available for countries to adopt in their preparation of national GHG inventories. Definitions ofterms Some of the terms used in the IPCC GHG inventory guidelines are source, sink, activity data, emission factor and removal factor. Source Any process or activity that releases a GHG (such as CO2 and CH4) into the atmosphere. A carbon pool can be a source of carbon to the atmosphere if less carbon is flowing into it than is flowing out of it.

Sink Any process, activity or mechanism that removes a GHG from the atmosphere. A given pool can be a sink for atmospheric carbon if during a given time interval more carbon flows into it than flows out of it.

Activity data (AD) Data on the magnitude of human activity resulting in emissions/ removals taking place during a given period of time (e.g. data on land area, area afforested, area converted to another land-use and roundwood extraction).

Emission factor (EE) A coefficient that relates the activity data to the amount of chemical compound that is the source of emissions. Emission factors are often based on a sample of measurement data, averaged to develop a representative rate of emission for a given activity level under a given set of operating conditions (e.g. above-ground biomass stock per hectare or soil organic carbon density). Removal factor Rate at which carbon is taken up from the atmosphere by terrestrial systems such as forests and grassland and sequestered in biomass and soil (e.g. above-ground biomass growth rate).

16.1 The Revised 1996 IPCC Guidelines

The Revised 1996 IPCC Guidelines have been extensively used by over 100 countries in preparing the national GHG inventory. The GHG inventories submitted have been compiled and synthesized by UNFCCC. The methodological issues largely relate to the following:

• Lack of compatibility between IPCC land/forest category/vegetation type/systems/formats and national circumstances or classification in most countries

• High uncertainty in inventory estimation

• Lack of clarity in reporting estimates of emissions/removals in managed natural forest

• Lack of consistency in estimating/reporting total biomass or only above-ground biomass

• Reporting total biomass covering either multiple carbon pools or a single pool, such as above-ground biomass; lack of consistency for comparability

• Guidance for below-ground biomass not provided

• Estimation (or differentiation) of managed (anthropogenically impacted) and natural forests

• Lack of methods for savannah/grassland

• Lack of methods for incorporating non-forest areas such as coffee, tea, coconut and cashew nut, as well as ambiguity about agroforestry

• Absence of linkage between biomass and soil carbon

° In Revised 1996 IPCC Guideline changes in stocks of biomass and soil carbon are estimated in different IPCC categories or worksheets and are not linked

16.2 The IPCC 2003 and 2006 Guidelines

The fundamental basis of the methodology of inventory rests upon two linked assumptions: (i) the flux of CO2 to/from the atmosphere is equal to changes in carbon stocks in the existing biomass and soils and (ii) changes in carbon stocks can be estimated by first establishing the rates of change in land-use and the practice used to bring about the change (e.g. burning, clear-cutting, selective cutting, change in silviculture or other management practice). This requires estimation of land use in the inventory year, conversion of forest land or grasslands, and the stocks of carbon in the land-use categories (those that are subjected to change and those that are not).

The unique feature of land-use sector is that it includes emissions as well as removals, unlike in other sectors where only GHG emissions are estimated. This sector encompasses all land-use categories of a country. The key improvements in the IPCC (2003, 2006) Guidelines with respect to GHG inventory for land-use categories over 1996 that are relevant to carbon inventory are summarized below:

• Adoption of six land-use categories forest land, cropland, grassland, wetland, settlements and other land to make the estimates consistent by covering all land-use categories over the years. These land-use categories are further disaggregated to account for the carbon dynamics, especially in the soil, due to land-use change into

° Land remaining in the same category such as forest land remaining forest or grassland remaining grassland (involving no change in land use). ° Land converted to another land-use category such as grassland or cropland converted to forest land.

• Adoption of key source or sink category analysis for different land-use categories, CO2 pools and non-CO2 gases to focus on the dominant land-use categories, GHGs and carbon pools.

• Adoption of three hierarchical tier methods that range from default emission factors and simple equations to the use of country-specific data and models to accommodate national circumstances (see Section 16.8 for details).

• Linking biomass and soil carbon in all land-use categories such as forests and croplands.

• Guidance for all the five carbon pools namely, above-ground biomass, below-ground biomass, deadwood, litter and soil organic carbon.

• Provision of generic methods to account for changes in stocks of carbon in biomass and soil in different land-use categories.

The IPCC (2003, 2006) provides guidance on the following steps for preparing the inventory:

1. Definition of managed land Divide all land into managed and unmanaged land, since GHG inventory is made only for lands subjected to anthropogenic effects, which, in other words, is managed land.

2. Land classification Develop a national land classification system applicable to all six land-use categories (forest land, cropland, grassland, wetland, settlements and other land) and further subdivide by climate, soil type and/or ecological regions appropriate for the country.

3. Compilation of data Compile data on the area and changes in the area in each land-use category and subcategory if available. Categorize land area by specific management systems defined for each land-use category, and by subcategory, if available. This categorization could provide the basis for assigning emission factors and stock-change factors required for calculation of CO2 emissions and removals.

4. Estimation of CO2 emissions and removal Estimate emissions and removals at the appropriate tier level based on key category analysis.

5. Estimation of uncertainties and adoption of quality assurance and quality control (QA/QC) procedures Use methods provided to estimate uncertainty.

6. Calculation oftotal inventory Sum CO2 emissions and removals over the inventory period for each land-use category and subcategory.

7. Reporting of inventory Using reporting tables, convert carbon stock changes to net emission or removals of CO2 by land-use categories.

8. Documentation and archiving Document and archive all information used to produce an inventory, including activity and other input data, emission factors, sources of data and data documentation, methods, description of model and QA/QC procedures and reports in addition to the results for each source category.

16.3 Carbon Inventory Methods for Land-Use Categories

Estimation of CO2 emissions and removals is the dominant component of GHG Inventory Guidelines. The basic principle in estimating CO2 emissions or removals from land-use categories involves combining the information on the extent to which human activity takes place (called activity data or AD) with the coefficients that quantify the emissions or removals per unit of the activity. These coefficients are called emission factors (EF) or removal factors (RF). Examples of activity data are the area of forest or plantations harvested or planted or supplied with fertilizers, and examples of emission or removal factors include growth rate of above-ground biomass, density of soil carbon and quantity of biomass burnt or harvested. The basic equation is as follows:

CO2 emission and removal = AD x EF or RF

Guidance is provided for estimating CO2 emissions and removals from all land-use categories under two conditions due to differing soil carbon dynamics:

• Land remaining in the same land-use category such as forest land remaining forest land

• Land converted to other land-use category such as grassland converted to forest land

Two methods are provided for carbon inventory, namely: (i) 'Gain-Loss' method and (ii) "Stock-Difference" method. Carbon inventory involves estimating the net emissions and removals for each land-use category for a given year, aggregated to all land-use categories.

16.4 What IPCC 2003 and 2006 Inventory Guidelines Provide

The inventory guidelines provide guidance separately for each of the carbon pools and for each of the land-use categories and also separately for the two subcategories, namely: (i) land remaining in the same category and (ii) land converted to other land-use category. The inventory guidelines provide the following information for each carbon pool separately.

Choice of method The approach to be adopted is discussed, particularly the equations to be used for calculating the carbon gain-loss for a given year or stock at different periods. The approach and methods are described for the three tiers, particularly in detail for Tier 1 (refer to Section 16.8). Choice of emission or removal factors The approach to selecting emission or removal factors is presented for the three Tiers.

Choice of activity data Approach to selecting the activity data is presented according to the three Tiers.

Calculation steps Brief steps in estimating carbon gain-loss or stock changes involving activity data and emission or removal factors are given by using a set of equations.

Uncertainty assessment The extent of and approach to estimating uncertainty in the emission or removal factors, activity data and the total estimate of CO2 emissions and removals are covered.

16.5 What IPCC 1996, 2003 and 2006 Inventory Guidelines do not Provide

The IPCC guidelines are meant to assist carbon inventory teams at the national level in calculating carbon emissions and removals and do not provide guidance on the following:

• Methods for estimating carbon stocks Methods for measuring or monitoring carbon in biomass or soil from different land-use categories are not given. The examples of methods are harvest and permanent plot method. The frequency of measurement of changes in carbon pools is not described.

• Methods for estimating growth rates Methods are not described for measurement and calculation of growth rates of biomass and soil carbon pools.

• Sampling methods and procedures Methods of selecting and locating the type, size and number of plots for measurement of carbon pools are not provided.

• Methods for determination of area Methods for estimating the area under a given land-use and marking of the boundary for a given land-use management practice are not given.

• Parameters to bee measured The parameters to be measured or monitored in the field or laboratory for calculating biomass and soil carbon are not given. Examples of parameters are tree DBH (diameter at breast height) and height, soil bulk density, soil organic carbon content and woody biomass density.

• Field and laboratory measurement techniques Methods and techniques for measuring the parameters for estimating biomass and soil carbon are not described. Examples of techniques include those for measuring tree height and DBH, soil bulk density and wood density.

• Calculation procedures Procedure for conversion of parameters (such as height, DBH, soil bulk density) measured into biomass or soil organic carbon density per hectare is not given.

• Models for carbon estimation Estimation or projection of biomass stock changes using models such as CO2FIX, PROCOMAP and CENTURY is not described.

Many countries have forest inventory programmes for monitoring biomass stocks and changes in those stocks. Data from such forest inventories could be used for the national carbon inventory. Guidance on preparing a forest inventory, particularly for above-ground biomass and commercial or merchantable timber is available in literature (Kangas and Maltamo 2006). However, the traditional forest inventory may have the following limitations for the national carbon inventory.

• Cropland, agroforestry and grassland categories are not included in the forest inventory

• Normally, forest inventory provides estimates of above-ground biomass, particularly commercial or merchantable timber, and it may not include estimates for soil organic carbon, below-ground biomass, deadwood and litter pools

• Non-tree biomass is not estimated even for forest lands

• Land-use changes or boundary shifts are not included

Therefore, there is a need for guidance on the methods of estimating activity data and emission factors to improve the estimates included in the national GHG inventory.

16.6 Application of Carbon Inventory Methods to National GHG Inventory

Activity data and emissions and removals factors are critical to a reliable and high-quality GHG inventory. The key activity data on area under different forest and plantation types, cropping systems, grassland and so on are collected in most countries for several purposes of planning and development and thus are often available, although data on changes in area are often limited. Even FAO and other international agencies publish data on the activity data. Thus, availability and quality of activity data are better than emission/removal factors for most countries.

However, the national GHG inventory process, particularly in the developing or tropical countries, is characterized by non-availability of emission and removal factors for different land-use categories, subcategories and land management systems. Even when available, the uncertainty level of the data is high, which makes the estimates in the emission inventory incomplete or characterized by high uncertainty. Majority of the developing countries use a large number of default carbon emission and removal factors provided in the IPCC guidelines, the Emission Factor Data Base (EFDB), FAO publications and other global data sources. The emission and removal factors are highly variable, often location-specific and likely to vary with soil, rainfall, altitude and management systems, even for a given forest type, plantation species, grassland or cropland systems.

Uncertainty in the estimates that make up the carbon inventory is likely to be high when global default values for parameters such as growth rates of above-ground biomass, biomass and soil carbon stocks are used. Developing a database on carbon stocks and growth rates of different carbon pools for various land-use categories (forest, cropland and grassland) and subcategories based on soil, rainfall and other agroclimatic conditions and management systems at subnational level can reduce such uncertainty.

The methods and guidelines provided in this handbook can be used for generating emission and removal factors required for estimating carbon gain-loss or stock changes at the national level for the GHG inventory. Nationally derived emission or removal factors for different land-use categories, subcategories and management systems at disaggregated level will enable a country to reduce uncertainty in the estimates of national GHG inventory. The methods provided in the earlier chapters could be adopted for generating emission and removal factors for different forest and plantation types, grassland management, cropland and agroforestry systems. Some of the key emission and removal factors required for the national CO2 inventory are

(i) Above-ground biomass stock and growth rates

(ii) Below-ground biomass stocks

(iii) Deadwood and litter stocks

(iv) Soil organic carbon stocks and rates of change

(v) Density of woody biomass

(vi) Biomass conversion and expansion factors

16.7 Approach to Generating Carbon Emission and Removal Factors for National GHG Inventories

Preparing a GHG inventory is a long-term and recurring process under the UNFCCC, which is why it is important for all countries to have long-term and definitive institutional arrangements for the process, particularly for land-use sectors. The following approach could be adopted for using carbon inventory methods to improve national GHG inventories.

16.7.1 Tier Definition and Selection for GHG Inventory

A tier represents a level of methodological complexity. A shift from lower tier to higher tier is associated with increased complexity, data requirements and accuracy, ultimately reducing uncertainty of the estimates. IPCC (2003, 2006) inventory guidelines provide three tiers, which implicitly progress from the least to the highest level of certainty in estimates as a function of

- Methodological complexity

- Regional specificity of model parameters

- Spatial resolution and extent of activity data

Tier 1 Tier 1 is the simplest and basic method to use, requiring minimal data. The activity data and emission factors, particularly the latter, are obtained from global data sources, such as FAO reports and websites. National-level activity data are often available but the availability of emission and removal factors is limited. The global or regional data sources are often in the form of aggregated or macro-level averages. Countries using Tier 1 methods usually use the national sources of activity data and default emission and removal factors from IPCC guidelines or the FAO database. Inventory estimates made using Tier 1 methods are associated with high uncertainty. Tier 2 Tier 2 uses the same methods or equations as those used in Tier 1, but the activity data and emission factors are derived from national sources. 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 categories. Country-defined emission factors are more appropriate for the climatic regions, land-use systems and management systems in the given country. Higher temporal and spatial resolution and more disaggregated activity data are typically used in Tier 2 to correspond to country-defined coefficients for specific regions and specialized land-use systems.

Tier 3 Higher-order methods are used in Tier 3, including models and inventory measurement systems tailored to address national circumstances, repeated over time, and driven by high-resolution activity data disaggregated at subnational level. These higher-order methods provide estimates of greater certainty than those obtained from the lower tiers. Such systems may include comprehensive field sampling repeated regularly and/or GIS-based systems of age class, production data, soils data and land-use and management activity data integrating several types of monitoring. A piece of land where a land-use change occurs can usually be tracked over time using remote sensing techniques. Models should undergo quality checks, audits and validations and be thoroughly documented.

Combining the tiers Although it is desirable to adopt higher tiers for all key land-use categories, subcategories and carbon pools, it may not be feasible due to data and resource limitations. The next best approach is to adopt a combination of tiers for increasing the accuracy of the inventory estimates. For example, Tier 2 could be adopted for activity data on a forest plantation and Tier 1 default estimates of mean annual above-ground biomass growth rate for the same land-use category. Further, Tier 2 estimates, based on location-specific studies, can be used for biomass stock and Tier 1 estimates for soil carbon stock for a given forest or plantation category. A combination of tiers, with preference for higher tiers, could be adopted

- For different land-use categories

- Within a given land-use category for different carbon pools

- Within a carbon pool, for activity data and emission factors

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