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

• Published in: Biogeosciences
• Main Authors: Xu, X, Riley, WJ, Koven, CD, Billesbach, DP, Chang, RYW, Commane, R, Euskirchen, ES, Hartery, S, Harazono, Y, Iwata, H, McDonald, KC, Miller, CE, Oechel, WC, Poulter, B, Raz-Yaseef, N, Sweeney, C, Torn, M, Wofsy, SC, Zhang, Z, Zona, D
• Format: Article in Journal/Newspaper
• Language: English
• Published: eScholarship, University of California 2016
• Subjects: Arctic
• Online Access: http://www.escholarship.org/uc/item/7bw6g6wg

© Author(s) 2016. Wetlands are the largest global natural methane (CH4/ source, and emissions between 50 and 70° N latitude contribute 10-30% to this source. Predictive capability of land models for northern wetland CH4emissions 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 CH4emission predictions from the Community Land Model 4.5 (CLM4.5-BGC) with siteto regional-scale observations. A comparison of the CH4fluxes 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 CH4emissions when compared with CarbonTracker CH4predictions. CLM4.5 CH4emission predictions agree well with growing season (May-September) CarbonTracker Alaskan regional-level CH4predictions and sitelevel observations. However, CLM4.5 underestimated CH4emissions in the cold season (October-April). The monthly atmospheric CH4mole 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 CH4mole fraction measurements from the Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) campaign. Both the tower and aircraft analyses confirm the underestimate of cold-season CH4emissions by CLM4.5. The greatest uncertainties in predicting the seasonal CH4cycle are from the wetland extent, coldseason CH4production and CH4transport processes. We recommend more cold-season experimental studies in highlatitude systems, which could improve the understanding and parameterization of ecosystem structure and function during this period. Predicted CH4emissions remain uncertain, but we show here that benchmarking against observations across spatial scales can inform model structural and parameter improvements.