Global lake CH4 emissions (1980-2023) simulated using the process-based model-LAKE2.6

While lakes play an important role in the 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 spatiotemporal representations. To address these uncertainties, 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 temperate lakes and 5 tropical (24 °S–24 °N) lakes with continuous flux observations covering from 2 months to 8 years, and then proposed a new parameterization scheme for global lake CH4 simulation based on site-level calibrations. For global model validation, flux observations in 155 lakes from temperate and boreal 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 85% of temperate and boreal lakes and 38% of tropical lakes exhibited simulated similar CH4 fluxes to observations, with biases of < ±50%. Based on these model calibration and validation results, we developed a global parameterization framework and applied it to simulate global lake CH4 emissions. Our estimates indicate that lakes emitted 17.7–20.1 Tg CH4 yr-1 during the period 1979–2023, showing an increasing trend of 0.02 Tg CH4 yr-2. This approach enhances the reliability of model performance when extrapolating from site-level measurements to global-scale estimates, thereby improving our ability to assess historical and future changes in global lake CH4 emissions.