There are about 304 million lakes in the world. Lakes can be classified into four major types according to their stratification: 1. Amictic Lakes which are always covered by ice (Antarctica and Arctic regions, very high altitude lakes); 2. Monomictic Lakes which have one turnover per year (Arctic and high altitude lakes and lower temperate region lakes); 3. Dimictic Lakes that turnover in spring and fall, and are covered by ice in winter (lakes in temperate regions); and 4. Polymictic Lakes that have multiple turnovers/mixings (shallower lakes from tropical region to high latitude region). This diversity of lake types is strongly linked to different climate and weather conditions and different types have different feedbacks to the climate and weather system. Natural lakes are dominated in area by a large number of small to medium lakes. These small to medium lakes are not resolvable in most of NWP/NCP models, and their effects are either ignored or crudely parameterized. As increasing computer power allows for increased model horizontal resolution, lakes become resolved features and inclusion of their effects become more important. The fresh water lake “FLAKE” model, proposed by Dmitrii Mironov (2008, DWD), is in use in regional (COSMO, HIRLAM), and global (UKMO, ECMWF) models. FLAKE is a two-layer model for fresh lakes that includes 1) a mixed-layer & thermocline, 2) temperature & energy budget calculations, 3) a sediment module, and 4) a snow-ice modules. It requires user-specified depth and turbidity, and it uses atmospheric forcing inputs. FLAKE has recently been coupled with the latest version of the Global Forecast System (GFSv15) at NCEP/EMC. In this study, sensitivity tests are conducted to test and evaluate lake effects in the model. Primary results show that the coupling improves the performance of the GFS.
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