Methane emissions from lakes will increase with climate warming. However, CH4 these emissions are not presently in the surface schemes of Global Climate Models (GCMs). Because climate projections depend on future atmospheric CH4 concentrations, a positive feedback loop is not simulated. To address this issue, a one-dimensional model was developed to simulate future CH4 diffusive and ebullitive fluxes from four Alaskan lakes. The model was hindcast for validation (1976-2005) and forecast for prediction (2071-2100) with one-way coupling to raw meteorological data from the CanESM2 ensemble GCM. Three climate warming scenarios (RCPs 2.6, 4.5 and 8.5) simulated bottom water to warm by up to 2.24{degree sign}C, increasing the CH4 flux from the lakes by 38 - 129%. However, RCP 2.6 and 4.5 led to stabilized temperatures and CH4 emissions by 2100, at levels of 0.63 - 1.21{degree sign}C and 38 - 67%, respectively, above the 1976-2005 averages. The CH4 diffusion parameterization was transferable between the four lakes; however, different ebullition parameterizations were required for the two deeper lakes (~6-7 m mean depth) versus the two shallower lakes (~1-3 m mean depth). Relative to using observed meteorological forcing, which had a cold bias (-0.15 to -0.63 {degree sign}C) and RMSE of 0.38 to 0.90 {degree sign}C, the GCM-forced models had a warm bias (+0.96 to +3.13{degree sign}C) and marginally higher RMSE (1.03 to 3.50{degree sign}C) compared to observations. The results support continued efforts to couple CH4 lake-emission models to GCMs without downscaling meteorological data, allowing feedback between CH4 dynamics and future climates to be modelled.

Inter-basin exchange of water and dissolved substances in lakes is often limited by topographic constrictions leading to spatially heterogeneous distributions of nutrients and plankton. Here, we identify the main factors controlling inter-basin exchange on seasonal and inter-annual time scales and investigate the impact of changes in climate and hydrology focusing mainly on the exchange between two basins of Lower Lake Constance (LLC). The analysis is based on multi-annual simulations of LLC, a sensitivity analysis, and numerical tracer experiments with a coupled 3-D hydrodynamic ice model (AEM3D). The seasonal course of water exchange is predominantly determined by the seasonal change in the current speed across the sill, vS, but also by changes in the area of the cross-section above the sill resulting from water level changes. The seasonal pattern of vS is linked to the presence of ice cover, the seasonal change in stratification and in water level. The impact of climate warming and hydrological change on water exchange therefore varies seasonally. Climate warming results in reduced ice cover and an earlier onset and longer duration of stratification, leading to enhanced inter-basin exchange especially during winter and spring, but not in summer. In contrast, increased water levels enhance inter-basin exchange especially in summer, because the increase in cross-sectional area associated with increased water levels coincides then with high vS. Finally, the fraction of water from Upper Lake Constance reaching the rather secluded basin Gnadensee increases with climate warming, implying a larger influence of the upstream conditions on Gnadensee.