WETCHIMP-WSL: Intercomparison of wetland methane emissions models over West Siberia

This article was published as a discussion paper in Biogeosciences Discussions Vol. 12, pp. 1907 - 1973 (2015). See http://hdl.handle.net/10871/17199 in ORE.Open access journalWetlands are the world's largest natural source of methane, a powerful greenhouse gas. The strong sensitivity of methane emissions to environmental factors such as soil temperature and moisture has led to concerns about potential positive feedbacks to climate change. This risk is particularly relevant at high latitudes, which have experienced pronounced warming and where thawing permafrost could potentially liberate large amounts of labile carbon over the next 100 years. However, global models disagree as to the magnitude and spatial distribution of emissions, due to uncertainties in wetland area and emissions per unit area and a scarcity of in situ observations. Recent intensive field campaigns across the West Siberian Lowland (WSL) make this an ideal region over which to assess the performance of large-scale process-based wetland models in a high-latitude environment. Here we present the results of a follow-up to the Wetland and Wetland CH4 Intercomparison of Models Project (WETCHIMP), focused on the West Siberian Lowland (WETCHIMP-WSL). We assessed 21 models and 5 inversions over this domain in terms of total CH4 emissions, simulated wetland areas, and CH4 fluxes per unit wetland area and compared these results to an intensive in situ CH4 flux data set, several wetland maps, and two satellite surface water products. We found that (a) despite the large scatter of individual estimates, 12-year mean estimates of annual total emissions over the WSL from forward models (5.34 ± 0.54 Tg CH4 yrg'1), inversions (6.06 ± 1.22 Tg CH4 yrg'1), and in situ observations (3.91 ± 1.29 Tg CH4 yrg'1) largely agreed; (b) forward models using surface water products alone to estimate wetland areas suffered from severe biases in CH4 emissions; (c) the interannual time series of models that lacked either soil thermal physics appropriate to the high latitudes or realistic emissions from unsaturated peatlands tended to be dominated by a single environmental driver (inundation or air temperature), unlike those of inversions and more sophisticated forward models; (d) differences in biogeochemical schemes across models had relatively smaller influence over performance; and (e) multiyear or multidecade observational records are crucial for evaluating models' responses to long-term climate change.COST Action TERRABITESNASAUS National Science Foundation (NSF) Science, Engineering and Education for Sustainability (SEES) Post-Doctoral Fellowship programNational Science and Engineering Research Council of Canada (NSERC) - visiting Post-Doctoral Fellowship.German Ministry of Education and Research - CarboPerm-ProjectSwiss National Science FoundationEuropean Commission FP7 project Past4FutureERC FP7 project EMBRACEUS National Science FoundationUS Department of EnergyTomsk State University Competitiveness Improvement ProgramEnvironment Research and Technology Development Fund (ERTDF), Ministry of Environment JapanRussian PresidentRussian Foundation for Basic ResearchNatural Environment Research Council (NERC)US Department of Energy under the Regional and Global Climate Modeling (RGCM) Program and the Next-Generation Ecosystem Experiments (NGEE Arctic) projec