## 2.12.1. Vertical Discretization[¶](#vertical-discretization "Permalink to this headline")
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Currently, there is one lake modeled in each grid cell (with prescribed or assumed depth _d_, extinction coefficient \\(\\eta\\), and fetch _f_), although this could be modified with changes to the CLM subgrid decomposition algorithm in future model versions. As currently implemented, the lake consists of 0-5 snow layers; water and ice layers (10 for global simulations and 25 for site simulations) comprising the “lake body;” 10 “soil” layers; and 5 bedrock layers. Each lake body layer has a fixed water mass (set by the nominal layer thickness and the liquid density), with frozen mass-fraction _I_ a state variable. Resolved snow layers are present if the snow thickness \\(z\_{sno} \\ge s\_{\\min }\\), where _s_min = 4 cm by default, and is adjusted for model timesteps other than 1800 s in order to maintain numerical stability (section [2.12.6.5](#modifications-to-snow-layer-logic-lake)). For global simulations with 10 body layers, the default (50 m lake) body layer thicknesses are given by: \\(\\Delta z\_{i}\\) of 0.1, 1, 2, 3, 4, 5, 7, 7, 10.45, and 10.45 m, with node depths \\(z\_{i}\\) located at the center of each layer (i.e., 0.05, 0.6, 2.1, 4.6, 8.1, 12.6, 18.6, 25.6, 34.325, 44.775 m). For site simulations with 25 layers, the default thicknesses are (m): 0.1 for layer 1; 0.25 for layers 2-5; 0.5 for layers 6-9; 0.75 for layers 10-13; 2 for layers 14-15; 2.5 for layers 16-17; 3.5 for layers 18-21; and 5.225 for layers 22-25. For lakes with depth _d_ \\(\\neq\\) 50 m and _d_ \\(\\ge\\) 1 m, the top layer is kept at 10 cm and the other 9 layer thicknesses are adjusted to maintain fixed proportions. For lakes with _d_ \\(<\\) 1 m, all layers have equal thickness. Thicknesses of snow, soil, and bedrock layers follow the scheme used over non-vegetated surfaces (Chapter [2.6](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/Soil_Snow_Temperatures/CLM50_Tech_Note_Soil_Snow_Temperatures.html#rst-soil-and-snow-temperatures)), with modifications to the snow layer thickness rules to keep snow layers at least as thick as _s_min (section [2.12.6.5](#modifications-to-snow-layer-logic-lake)).

