### 2.2.1.4. Phenology and vegetation burial by snow[¶](#phenology-and-vegetation-burial-by-snow "Permalink to this headline")

When the biogeochemistry model is inactive, leaf and stem area indices (m2 leaf area m\-2 ground area) are updated daily by linearly interpolating between monthly values. Monthly PFT leaf area index values are developed from the 1-km MODIS-derived monthly grid cell average leaf area index of [Myneni et al. (2002)](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#mynenietal2002), as described in [Lawrence and Chase (2007)](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#lawrencechase2007). Stem area ndex is calculated from the monthly PFT leaf area index using the methods of [Zeng et al. (2002)](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#zengetal2002). The leaf and stem area indices are adjusted for vertical burying by snow ([Wang and Zeng 2009](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#wangzeng2009)) as

(2.2.1)[¶](#equation-2-1 "Permalink to this equation")\\\[A=A^{\*} ( 1-f\_{veg}^{sno} )\\\]

where \\(A^{\*}\\) is the leaf or stem area before adjustment for snow, \\(A\\) is the remaining exposed leaf or stem area, \\(f\_{veg}^{sno}\\) is the vertical fraction of vegetation covered by snow

(2.2.2)[¶](#equation-2-2 "Permalink to this equation")\\\[\\begin{split}{f\_{veg}^{sno} = \\frac{z\_{sno} -z\_{bot} }{z\_{top} -z\_{bot} } \\qquad {\\rm for\\; tree\\; and\\; shrub}} \\\\ {f\_{veg}^{sno} = \\frac{\\min \\left(z\_{sno} ,\\, z\_{c} \\right)}{z\_{c} } \\qquad {\\rm for\\; grass\\; and\\; crop}}\\end{split}\\\]

where \\(z\_{sno} -z\_{bot} \\ge 0,{\\rm \\; }0\\le f\_{veg}^{sno} \\le 1\\), \\(z\_{sno}\\) is the depth of snow (m) (Chapter [2.8](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/Snow_Hydrology/CLM50_Tech_Note_Snow_Hydrology.html#rst-snow-hydrology)), and \\(z\_{c} = 0.2\\) is the snow depth when short vegetation is assumed to be completely buried by snow (m). For numerical reasons, exposed leaf and stem area are set to zero if less than 0.05. If the sum of exposed leaf and stem area is zero, then the surface is treated as snow-covered ground.

