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Land surfaces

Within each grid box there are several different types of ground surface, each covering a proportion of the area (Fig2.1.18 and Fig2.1.19).  The ground types are described by a set of "tiles" for:  

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Table 1: Assignment of height characteristic and vegetation coverage for each type of vegetation or surface.  In cases of snow, vegetation assigned as high (H) can have snow cover beneath; vegetation assigned as low (L) are considered as snow covered.  See "Modelling snow" section.  The assigned vegetation coverage gives information to the soil model regarding transpiration and root depth.  See "Modelling soil" section.   Albedo values are associated with leaf are index. See "Leaf area index" section. 

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Fig2.1.18: An example of the variability of land surface within an approximate grid box illustrating the difficulty in assigning representative HTESSEL "tiles" for the whole grid square area.  The red lines show the extent of a very approximate 9km x 9km schematic HRES * and and ENS grid square.   There is a large variation in ground surface type and the proportional contribution to the heat, moisture and momentum fluxes are difficult to assess.  For this grid box, high vegetation 'tile' covers about 5%, low vegetation 'tile' covers about 70%, estuary (lake) 'tile' covers about 20%, and the remaining area about 5% is considered a bare ground 'tile'.  There is no 'tile' for urban areas so is considered as bare ground.  An ENS meteogram is interpolated from the four grid points surrounding a given station within the box.  See Section on Selection of gridpoints for Meteograms for details.

Fig2.1.19: An example of the variability of land surface within an approximate grid box illustrating the difficulty in assigning a representative HTESSEL "tiles" for the whole grid square area.  The red lines show the extent of a very approximate 9km x 9km schematic HRES * and and ENS grid square.  There is some variation in ground surface type but it is predominantly covered by evergreen needle-leaf trees.  The proportional contribution to the heat, moisture and momentum fluxes are rather simpler to assess.  In winter snow the appropriate tile would be forest snow.  Runoff would be rapid over Rocky Mountain sides, much slower over low-lying river valleys   For this grid box, high vegetation 'tile' covers about 75%, low vegetation 'tile' covers about 5%, lake 'tile' covers about 5%, and the remaining area about 15% is considered a bare ground 'tile'.  This iconsists of 5% rock area but 10% urban area which is also considered as bare ground.  An  ENS meteogram is interpolated from the four grid points surrounding a given station within the box.  See Section on Selection of gridpoints for Meteograms for details.

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