Anthropogenic and natural methane fluxes in Switzerland synthesized within a spatially explicit inventory

We present the first high-resolution (500m x 500m) gridded methane (CH4) emission inventory for Switzerland, which integrates 90% of the national emission totals reported to the United Nations Framework Convention on Climate Change (UNFCCC) and recent CH4 flux studies conducted by research groups across Switzerland. In addition to anthropogenic emissions, we also include natural and semi-natural CH4 fluxes, i.e., emissions from lakes and reservoirs, wetlands, wild animals as well as uptake by forest soils. National CH4 emissions were disaggregated using detailed geostatistical information on source locations and their spatial extent and process-or area-specific emission factors. In Switzerland, the highest CH4 emissions in 2011 originated from the agricultural sector (150 GgCH(4) yr(-1)), mainly produced by ruminants and manure management, followed by emissions from waste management (15 GgCH(4) yr(-1)) mainly from landfills and the energy sector (12 GgCH(4) yr(-1)), which was dominated by emissions from natural gas distribution. Compared with the anthropogenic sources, emissions from natural and semi-natural sources were relatively small (6 GgCH(4) yr(-1)), making up only 3% of the total emissions in Switzerland. CH4 fluxes from agricultural soils were estimated to be not significantly different from zero (between -1.5 and 0 GgCH(4) yr(-1)), while forest soils are a CH4 sink (approx. -2.8 GgCH(4) yr(-1)), partially offsetting other natural emissions. Estimates of uncertainties are provided for the different sources, including an estimate of spatial disaggregation errors deduced from a comparison with a global (EDGAR v4.2) and an European (TNO/MACC) CH4 inventory. This new spatially explicit emission inventory for Switzerland will provide valuable input for regional-scale atmospheric modeling and inverse source estimation.