Completeness Time series Quality Assurance Quality Control and Reporting

To achieve completeness, all the major animal categories managed in the country should be considered. In the event that animals are included in the inventory for which default data are not available and for which no guidelines are provided, the emissions estimate should be developed using the same general principles presented in the discussion in Section 10.2.

Care must be taken to use a consistent set of estimates for the CH4 conversion factors over time. In some cases, there may be reasons to modify methane conversion factors over time. These changes may be due to the implementation of explicit greenhouse gas (GHG) mitigation measures, or may be due to changing agricultural practices such as feed conditions or other management factors without regard to GHGs. Regardless of the driver of change, the data and methane conversion factors used to estimate emissions must reflect the change in farm practices. If methane conversion factors over a time series are affected by a change in management practice and/or the implementation of GHG mitigation measures, the inventory compiler should ensure that the inventory data reflect these practices. The inventory text should thoroughly explain how the changes in management practice and/or implementation of mitigation measures has affected the time series of methane conversion factors. For general good practice guidance on developing a consistent time series, see Volume 1, Chapter 5 (Time Series Consistency).

It is good practice to implement quality control checks as outlined in Volume 1, Chapter 6 (Quality

Assurance/Quality Control and Verification). In addition to the guidance in Volume 1, specific procedures of relevance to this source category are outlined below:

Activity data check

• The inventory compiler should review livestock data collection methods, in particular checking that livestock subspecies data were collected and aggregated correctly. The data should be cross-checked with previous years to ensure the data are reasonable and consistent with the expected trend. Inventory compilers should document data collection methods, identify potential areas of bias, and evaluate the representativeness of the data. Population modeling can be used to support this approach.

Review of emission factors

• If using the Tier 2/Tier 3 method, the inventory compiler should cross-check country-specific factors against the IPCC defaults. Significant differences between country-specific factors and default factors should be explained and documented.

External review

• If Tier 2/Tier 3 method is used, the inventory compiler is encouraged to conduct national and international expert review, including from industry, academic institutions, and extension expertise.

• It is important to maintain internal documentation on review results.

To improve transparency, emission estimates from this source category should be reported along with the activity data and emission factors used to determine the estimates.

The following information should be documented:

• All activity data including animal population data by category and region.

• Activity data documentation including:

(i) The sources of all activity data used in the calculations (i.e., complete citation for the statistical database from which data were collected);

(ii) The information and assumptions that were used to develop the activity data, in cases where activity data were not directly available from databases; and

(iii) The frequency of data collection, and estimates of accuracy and precision.

• If Tier 1 method is used, all default emission factors used in the estimation of emissions for the specific animal categories.

(ii) DE values estimated or taken from other studies; and

(iii) Full documentation of the data used including their references.

• For inventories in which country- or region-specific emission factors are used or in which new methods, such as Tier 3 are used, the scientific basis of these emission factors and the principles of the new method should be thoroughly documented. Documentation should include definitions of input parameters and a description of the principle and process by which these emission factors and methods are derived, as well as describing sources and magnitudes of uncertainties.

10.4 METHANE EMISSIONS FROM MANURE MANAGEMENT

This section describes how to estimate CH4 produced during the storage and treatment of manure, and from manure deposited on pasture. The term 'manure' is used here collectively to include both dung and urine (i.e., the solids and the liquids) produced by livestock. The emissions associated with the burning of dung for fuel are to be reported under Volume 2 (Energy), or under Volume 5 (Waste) if burned without energy recovery. The decomposition of manure under anaerobic conditions (i.e., in the absence of oxygen), during storage and treatment, produces CH4. These conditions occur most readily when large numbers of animals are managed in a confined area (e.g., dairy farms, beef feedlots, and swine and poultry farms), and where manure is disposed of in liquid-based systems. Emissions of CH4 related to manure handling and storage are reported under 'Manure Management.'

The main factors affecting CH4 emissions are the amount of manure produced and the portion of the manure that decomposes anaerobically. The former depends on the rate of waste production per animal and the number of animals, and the latter on how the manure is managed. When manure is stored or treated as a liquid (e.g., in lagoons, ponds, tanks, or pits), it decomposes anaerobically and can produce a significant quantity of CH4. The temperature and the retention time of the storage unit greatly affect the amount of methane produced. When manure is handled as a solid (e.g., in stacks or piles) or when it is deposited on pastures and rangelands, it tends to decompose under more aerobic conditions and less CH4 is produced.

10.4.1 Choice of method

There are three tiers to estimate CH4 emissions from livestock manure. Guidance for determining which tier to use is shown in Figure 10.3 decision tree.

Tier 1

A simplified method that only requires livestock population data by animal species/category and climate region or temperature, in combination with IPCC default emission factors, to estimate emissions. Because some emissions from manure management systems are highly temperature dependent, it is good practice to estimate the average annual temperature associated with the locations where manure is managed.

Tier 2

A more complex method for estimating CH4 emissions from manure management should be used where a particular livestock species/category represents a significant share of a country's emissions. This method requires detailed information on animal characteristics and manure management practices, which is used to develop emission factors specific to the conditions of the country.

Tier 3

Some countries for which livestock emissions are particularly important may wish to go beyond the Tier 2 method and develop models for country-specific methodologies or use measurement-based approaches to quantify emission factors.

The method chosen will depend on data availability and national circumstances. Good practice in estimating CH4 emissions from manure management systems entails making every effort to use the Tier 2 method, including calculating emission factors using country-specific information. The Tier 1 method should only be used if all possible avenues to use the Tier 2 method have been exhausted and/or it is determined that the source is not a key category or subcategory.

Regardless of the method chosen, the animal population must first be divided into categories as described in Section 10.2 that reflect the varying amounts of manure produced per animal.

The following four steps are used to estimate CH4 emissions from manure management:

Step 1: Collect population data from the Livestock Population Characterisation (see Section 10.2).

Step 2: Use default values or develop country-specific emission factors for each livestock subcategory in terms of kilograms of methane per animal per year.

Step 3: Multiply the livestock subcategory emission factors by the subcategory populations to estimate subcategory emissions, and sum across the subcategories to estimate total emissions by primary livestock species.

Step 4: Sum emissions from all defined livestock species to determine national emissions.

Figure 1G.3 Decision tree for CH4 emissions from Manure Management

Figure 1G.3 Decision tree for CH4 emissions from Manure Management

Note:

1: 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.

2: As a rule of thumb, a livestock species would be significant if it accounts for 25-30% or more of emissions from the source category.

Equation 10.22 shows how to calculate CH4 emissions from manure management:

Equation 10.22 shows how to calculate CH4 emissions from manure management:

Where:

CH4Manure = CH4 emissions from manure management, for a defined population, Gg CH4 yr-1 EF(T) = emission factor for the defined livestock population, kg CH4 head-1 yr-1 N(T) = the number of head of livestock species/category T in the country T = species/category of livestock

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