Evaluation of CH4MOD wetland and Terrestrial Ecosystem Model (TEM) used to estimate global CH 4 emissions from natural wetlands

Li, Tingting; Lu, Yanyu; Yu, Lingfei; Sun, Wenjuan; Zhang, Qing; Zhang, Wen; Wang, Guocheng; Qin, Zhangcai; Yu, Lijun; Li, Hailing; Zhang, Ran

Wetlands are the largest and most uncertain natural sources of atmospheric methane (inline-formulaCH4). Several process-based models have been developed to quantify the magnitude and estimate spatial and temporal variations in inline-formulaCH4 emissions from global wetlands. Reliable models are required to estimate global wetland inline-formulaCH4 emissions. This study aimed to test two process-based models, CH4MODinline-formulawetland and Terrestrial Ecosystem Model (TEM), against the inline-formulaCH4 flux measurements of marsh, swamp, peatland and coastal wetland sites across the world; specifically, model accuracy and generality were evaluated for different wetland types and in different continents, and then the global inline-formulaCH4 emissions from 2000 to 2010 were estimated. Both models showed similar high correlations with the observed seasonal/annual total inline-formulaCH4 emissions, and the regression of the observed versus computed total seasonal/annual inline-formulaCH4 emissions resulted in inline-formulaR2 values of 0.81 and 0.68 for CH4MODinline-formulawetland and TEM, respectively. The CH4MODinline-formulawetland produced accurate predictions for marshes, peatlands, swamps and coastal wetlands, with model efficiency (EF) values of 0.22, 0.52, 0.13 and 0.72, respectively. TEM produced good predictions for peatlands and swamps, with EF values of 0.69 and 0.74, respectively, but it could not accurately simulate marshes and coastal wetlands (EF inline-formula<0). There was a good correlation between the simulated inline-formulaCH4 fluxes and the observed values on most continents. However, CH4MODinline-formulawetland showed no correlation with the observed values in South America and Africa. TEM showed no correlation with the observations in Europe. The global inline-formulaCH4 emissions for the period 2000–2010 were estimated to be 105.31 inline-formula± 2.72 Tg yrinline-formula−1 by CH4MODinline-formulawetland and 134.31 inline-formula± 0.84 Tg yrinline-formula−1 by TEM. Both models simulated a similar spatial distribution of inline-formulaCH4 emissions globally and on different continents. Marshes contribute 36 %–39 % of global inline-formulaCH4 emissions. Lakes/rivers and swamps are the second and third greatest contributors, respectively. Other wetland types account for only approximately 20 % of global emissions. Based on the model applicability, if we use the more accurate model, i.e., the one that performs best as evidenced by a higher model efficiency and a lower model bias, to estimate each continent and wetland type, we obtain a new assessment of 116.99–124.74 Tg yrinline-formula−1 for the global inline-formulaCH4 emissions for the period 2000–2010. Our results imply that performance at a global scale may conceal model uncertainty. Efforts should be made to improve model accuracy for different wetland types and regions, particularly hotspot regions, to reduce the uncertainty in global assessments.

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Li, Tingting / Lu, Yanyu / Yu, Lingfei / et al: Evaluation of CH4MODwetland and Terrestrial Ecosystem Model (TEM) used to estimate global CH4 emissions from natural wetlands. 2020. Copernicus Publications.

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