| 28 Mar 2025
A new biogeochemical modelling framework (FLaMe v1.0) for lake methane emissions on the regional scale: Development and application to the European domain
Abstract. This study presents a new physical-biogeochemical modelling framework for simulating lake methane (CH4) emissions at regional scales. The new model, FLaMe v1.0 (Fluxes of Lake Methane), rests on an innovative, computationally efficient lake clustering approach that enables the simulation of CH4 emissions across a large number of lakes. Building on the Canadian Small Lake Model (CSLM) that simulates the lake physics, we develop a suite of biogeochemical modules to simulate transient dynamics of organic Carbon (C), Oxygen (O2), and CH4 cycling. We first test the performance of FLaMe by analyzing physical and biogeochemical processes in two representative lakes (an oligotrophic, deep lake driven by cold climate versus a trophic, shallow lake driven by warm climate). Next, we evaluate the model by comparing simulated and observed timeseries of CH4 emissions in four well-surveyed lakes. We then apply FLaMe at the European scale to evaluate simulated diffusive and ebullitive lake CH4 fluxes against in-situ measurements in both boreal and central European regions. Finally, we provide a first assessment of the spatio-temporal variability in CH4 emissions from European lakes smaller than 1000 km2 (n=108407, total area = 1.33x105 km2), indicating a total emission of 0.97±0.23 Tg CH4 yr-1, with the uncertainty constrained by combining FLaMe and machine learning techniques. Moreover, 30 % and 70 % of these CH4 emissions are through diffusive and ebullitive pathways, respectively. Annually averaged CH4 emission rates per unit lake area during 2010–2016 have a South-to-North decreasing gradient, resulting in a mean over the European domain as 7.39 g CH4 m-2 yr-1. Our simulations reveal a strong seasonality in European lake CH4 emissions, with late summer emissions nearly ten times higher than winter values. This pronounced seasonal variation highlights the importance of accounting for the sub-annual variability in CH4 emissions to accurately constrain regional CH4 budgets. In the future, FLaMe could be embedded into Earth System Models to investigate the feedback between climate warming and global lake CH4 emissions.
