Validation and sensitivity analysis of lake methane dynamics in Energy Exascale Earth System Model
Methane (CH4) is the second most important greenhouse gases just behind carbon dioxide. Recent studies showed that half of global CH4 emissions could come from highly variable aquatic ecosystems, including substantial emissions from lakes. However, lake CH4 dynamics has not yet been represented in Earth system models and thus the feedback between lake methane and climate is largely unknown. In this study, we developed a lake biogeochemical model in Energy Exascale Earth System Model (E3SM) that represents CH4 production, CH4 oxidation and CH4 transport through diffusion and ebullition. We used a surrogate-model based parameter calibration method to analyze the sensitive model parameters and calibrate them simultaneously. The model is validated against a global lake CH4 dataset that is compiled from literature reviews and includes data from over 100 lakes larger than 0.1 km2 across the globe. In addition, site-level model data comparison at sites with detailed CH4 dynamics data is also performed. We also test the possibility to improve the model performance by representing CH4 production in oxic water layers and using alternative algorithms for CH4 oxidation. The developed model may enable realistic predictions of the global CH4 cycle under climate change.