Climate Change Impacts on Surface Heat Fluxes in a Deep Monomictic Lake

Abstract

Turbulent and radiative energy exchanges between lakes and the atmosphere play an important role in determining the process of lake-mixing and stratification, including how lakes respond to climate and to climate change. Here we used a one-dimensional hydrodynamic lake model to assess seasonal impacts of climate change on individual surface heat flux components in Lough Feeagh, Ireland, a deep, monomictic lake. We drove the lake model with an ensemble of outputs from four climate models under three future greenhouse gas scenarios from 1976 to 2099. In these experiments, the results showed significant increases in the radiative budget that were largely counteracted by significant increases in the turbulent fluxes. The combined change in the individual surface heat fluxes led to a change in the total surface heat flux that was small, but sufficient to lead to significant changes in the volume-weighted average lake temperature. The largest projected changes in total surface heat fluxes were in spring and autumn. Both spring heating and autumnal cooling significantly decreased under future climate conditions, while changes to total surface heat fluxes in winter and summer were an order of magnitude lower. This led to counter-intuitive results that, in a warming world, there would be less heat not more entering Lough Feeagh during the springtime, and little change in net heating over the summer or winter compared to natural climate conditions, projected increases in the volume-weighted average lake temperature were found to be largely due to reduced heat loss during autumn.