Choice of Emission Factors. Tier 1 Emission factors for CH4 via diffusion and ebullition from the reservoir surface, EFCH4 age>20,j in the six aggregated climate zones are provided in Table 7.9. The emission factors integrate both spatial and temporal variations and have been derived from the application of empirical models to a large number of reservoirs (>6000) with a worldwide distribution and are averaged per climate zone. See Annex 7.1 for details of how default emissions factors were derived. TABLE 7.9 (NEW) CH4 EMISSION FACTORS FOR RESERVOIRS OLDER THAN 20 YEARS (> 20 YEARS) – Flooded Land Remaining Flooded Land Aggregated Climate Zone CH4 Emission Factors EFCH4 age>20,j (kg CH4 ha-1 year-1) j Average Lower and upper 95% CI of mean N Boreal 1 13.6 7.3-19.9 96 Cool Temperate 2 54.0 48.3-59.5 1879 Warm temperate/dry 3 150.9 133.3-168.1 578 Warm temperate/moist 4 80.3 74.0-86.0 1946 Tropical dry/montane 5 283.7 261.9-305.8 710 Tropical moist/wet 6 141.1 131.1-152.7 805
Choice of Emission Factors. Tier 1 Tier 1 emission factors for agriculture and aquaculture ponds, and from canals and ditches, are provided in Table 7.12. Emissions from ponds are separated into Freshwater Ponds with water column salinity < 18 ppt and Saline Ponds with salinity of > 18 ppt, consistent with the 2013 Wetlands Supplement (Chapter 4, Annex 4A.1 salinity- based definitions). At present, available data are not sufficient to derive emission factors for any category by climate zone, or to disaggregate emissions from canals, drainage channels and ditches, which are therefore considered as a single Tier 1 category. Disaggregation by surrounding land-use, nutrient loading and/or yield is also not currently possible at Tier 1. For ditches in organic soils, the Tier 1 emissions factors presented in Table 2.4 of the 2013 Wetlands Supplement may be used. TABLE 7.12 (NEW) CH4 EMISSION FACTORS FOR OTHER CONSTRUCTED WATERBODIES (FRESHWATER PONDS, SALINE PONDS, CANALS, DRAINAGE CHANNELS AND DITCHES) Waterbody type w Climate zone EFCH4 a (kg CH4 ha-1 yr-1) 95% confidence intervalsb (kg CH4 ha-1 yr-1) No. of sites Saline ponds 1 All 00 00-00 00 Freshwater and brackish ponds 2 All 183 118-228 68 Canals and ditchesc 3 All 000 000-000 24d a Emissions factors for each category were calculated from the mean of log10-transformed values, because untransformed observations showed a positively skewed distribution in all cases b 95% confidence intervals shown are derived from standard errors, and thus represent the uncertainty in the mean emission factor rather than the variability of the original measurements. c For Emission Factor for ditches in organic soils refer to Table 2.4, 2013 Wetlands Supplement. dDitch data are mostly aggregated to study level, where studies reported multiple measurements from the same ditch network or from sites in close proximity; therefore the total number of individual ditches used to derive the emission factor exceeds the number shown. References. Saline ponds: (Xxxxxxx et al. 2016), (Xxxxxxxx et al. 2017), (Xxxx et al. 2015), (Xxx et al. 2013), (Xxxxxxxxxx et al. 2008), (Xxxxxxx et al. 2016), (Xxxx et al. 2015). Xxxxxxxxxx and xxxxxxxx ponds: (Xxxxx-Xxxxxxx et al. 1977), (Xxxxxx et al. 2000), (Grinham 2018), (Xx et al. 2016), (Xxxxx 2016), (Xxx et al. 2017), (Xxxxxxx et al. 1996), (Xxxxxxxxxxx et al. 2014), (Xxxxxx et al. 2014), (Xxxxxxxx & Xxxxxxxxxx 2005), (xxx Xxxxxx 2015), (Xxxxx et al. 2000), (Xxxxx et al. 2017), (Xxxx et al. 2017), (Xxx et al. 2016). Canals ...
