Towards a process-based estimation of global lake methane emissions using LAKE2.6

Abstract. While lakes play an important role in global methane (CH₄) budget, the present meta-analysis based global estimates produce large uncertainties (16.5 to 185 Tg CH₄ yr^-1), which were often due to lacking sufficient geographical and spatio-temporal representations. Here, we applied a one-dimensional process-based CH₄ emission model (LAKE2.6) to simulate global lake CH₄ emissions. We first calibrated the model in 10 boreal and temperate lakes and 5 tropical (24 °S–24 °N) lakes with continuous flux observations spanning 2 months to 8 years, and subsequently proposed a novel parameterization scheme for global lake CH₄ simulation based on these site-level calibrations. For global model validation, flux observations in 155 lakes from boreal and temperate regions and 21 lakes from tropical regions were collected, ranging in depth from 0.1 to 572 m and in size from 6 m² to 67,075 km². We found that simulated CH₄ fluxes in 85 % of boreal and temperate lakes and 38 % of tropical lakes were consistent with observations, with relative biases within ±50 %. Based on these model calibration and validation results, we established a global parameterization framework and applied it to simulate global CH₄ simulations. Our estimates show that global lakes (>10 ha) emitted 17.7–20.1 Tg CH₄ yr^-1 during the period 1979–2023. This approach improves the reliability of model extrapolations from site-level measurements to the global-scale, thus strengthening our ability to assess historical and future changes in global lake CH₄ emissions.