Evaluation of two process-based models used to estimate global CH4 emissions from natural wetlands

Abstract

<p>Reliable models are required to estimate global wetland CH<sub>4</sub> emissions. This study aimed to test two process-based models, CH4MOD<sub>wetland</sub> and TEM, against the CH<sub>4</sub> flux measurements of marsh, swamps, 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 CH<sub>4</sub> emissions from 2000 to 2010 were estimated. Both models showed similar high correlations with the observed seasonal CH<sub>4</sub> emissions, and the regression of the observed versus computed total seasonal CH<sub>4</sub> emissions resulted in R<sup>2</sup> values of 0.78 and 0.72 by CH4MOD<sub>wetland</sub> and TEM, respectively. The CH4MOD<sub>wetland</sub> predicted more accurately in marsh, peatland and coastal wetlands, with model efficiency (EF) values of 0.22, 0.55 and 0.72, respectively; however, the model showed poor performance in swamps (EF<0). The TEM model predicted better in peatland and swamp, with EF values of 0.77 and 0.71, respectively, but it could not accurately simulate the marsh and coastal wetland (EF<0). There was a good correlation between the simulated CH<sub>4</sub> fluxes and the observed values on most continents. However, CH4MOD<sub>wetland</sub> showed no correlation with the observed values in South America and Africa. TEM showed no correlation with the observations in Europe. The global CH<sub>4</sub> emissions for the period 2000­­–2010 were estimated to be 105.31±2.72 Tg yr<sup>-1</sup> by CH4MOD<sub>wetland</sub> and 134.31±0.84 Tg yr<sup>-1</sup> by TEM. Both models simulated a similar spatial distribution of CH<sub>4</sub> emissions across the world and among continents. Marsh contributes 36%–39% to global CH<sub>4</sub> emissions. Lakes and rivers and swamp are the second and third contributors, respectively. Other wetland types account for only approximately 20% of global emissions. Based on the models’ generality, if we use the more accurate model to estimate each continent/wetland type, we obtain a new assessment of 116.99–124.74 Tg yr<sup>-1 </sup>for the global CH<sub>4</sub> emissions for the period 2000–2010.</p>