Climate regions are classified in order to apply emission and stock change factors for estimating biomass, dead organic matter and soil C stock changes. The default climate classification is provided in Figure 3A.5.1 and can be derived using the classification scheme in Figure 3A.5.2. This classification should be used for Tier 1 methods because the default emission and stock change factors were derived using this scheme. Note that climate regions are further subdivided into ecological zones to apply the Tier 1 method for estimating biomass C stock changes (see Table 4.1, Chapter 4). Inventory compilers have the option of developing a country-specific climate classification if using Tier 2 and 3 methods, along with country-specific emission and stock change factors. It is good practice to apply the same classification, either default or country-specific, across all land-use types. Thus, stock change and emission factors are assigned to each pool in a national inventory using a uniform classification of climate.
Soils are classified in order to apply reference C stocks and stock change factors for estimation of soil C stock changes, as well as the soil N2O emissions (i.e., organic soils must be classified to estimate N2O emissions following drainage). Organic soils are found in wetlands or have been drained and converted to other land-use types (e.g., Forest Land, Cropland, Grassland, Settlements). Organic soils are identified on the basis of criteria 1 and 2, or 1 and 3 listed below (FAO 1998):
1. Thickness of organic horizon greater than or equal to 10 cm. A horizon of less than 20 cm must have 12 percent or more organic carbon when mixed to a depth of 20 cm.
2. Soils that are never saturated with water for more than a few days must contain more than 20 percent organic carbon by weight (i.e., about 35 percent organic matter).
3. Soils are subject to water saturation episodes and has either:
a. At least 12 percent organic carbon by weight (i.e., about 20 percent organic matter) if the soil has no clay; or b. At least 18 percent organic carbon by weight (i.e., about 30 percent organic matter) if the soil has 60% or more clay; or c. An intermediate, proportional amount of organic carbon for intermediate amounts of clay.
All other types of soils are classified as mineral. A default mineral soil classification is provided in Figure 3A.5.3 for categorizing soil types based on the USDA taxonomy (USDA, 1999) and Figure 3A.5.4 for the World Reference Base for Soil Resources Classification (FAO, 1998) (Note: Both classifications produce the same default IPCC soil types). The default mineral soil classification should be used with Tier 1 methods because default reference C stock and stock change factors were derived according to these soil types. Inventory compilers have the option of developing a country-specific classification for mineral and/or organic if applying Tiers 2 and 3 methods, in combination with developing country-specific reference C stocks and stock change factors (or emission factors in the case of organic soils). It is good practice to use the same classification of soils across all land-use types.
Figure 3A.5.1 Delineation of major climate zones, updated from the 1996 IPCC Guidelines.
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