A multi-scale comparison of modeled and observed seasonal methane emissions in northern wetlands

• Published in: Biogeosciences
• Main Authors: X. Xu, W. J. Riley, C. D. Koven, D. P. Billesbach, R. Y.-W. Chang, R. Commane, E. S. Euskirchen, S. Hartery, Y. Harazono, H. Iwata, K. C. McDonald, C. E. Miller, W. C. Oechel, B. Poulter, N. Raz-Yaseef, C. Sweeney, M. Torn, S. C. Wofsy, Z. Zhang, D. Zona
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2016
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Arctic
• Online Access: https://doi.org/10.5194/bg-13-5043-2016; https://doaj.org/article/0903b4730cdc4fc581fac89ec77a5401

Wetlands are the largest global natural methane (CH 4 ) source, and emissions between 50 and 70° N latitude contribute 10–30 % to this source. Predictive capability of land models for northern wetland CH 4 emissions is still low due to limited site measurements, strong spatial and temporal variability in emissions, and complex hydrological and biogeochemical dynamics. To explore this issue, we compare wetland CH 4 emission predictions from the Community Land Model 4.5 (CLM4.5-BGC) with site- to regional-scale observations. A comparison of the CH 4 fluxes with eddy flux data highlighted needed changes to the model's estimate of aerenchyma area, which we implemented and tested. The model modification substantially reduced biases in CH 4 emissions when compared with CarbonTracker CH 4 predictions. CLM4.5 CH 4 emission predictions agree well with growing season (May–September) CarbonTracker Alaskan regional-level CH 4 predictions and site-level observations. However, CLM4.5 underestimated CH 4 emissions in the cold season (October–April). The monthly atmospheric CH 4 mole fraction enhancements due to wetland emissions are also assessed using the Weather Research and Forecasting-Stochastic Time-Inverted Lagrangian Transport (WRF-STILT) model coupled with daily emissions from CLM4.5 and compared with aircraft CH 4 mole fraction measurements from the Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) campaign. Both the tower and aircraft analyses confirm the underestimate of cold-season CH 4 emissions by CLM4.5. The greatest uncertainties in predicting the seasonal CH 4 cycle are from the wetland extent, cold-season CH 4 production and CH 4 transport processes. We recommend more cold-season experimental studies in high-latitude systems, which could improve the understanding and parameterization of ecosystem structure and function during this period. Predicted CH 4 emissions remain uncertain, but we show here that benchmarking against observations across spatial scales can inform model structural and parameter ...