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Leaf area index
The impact of vegetation on interception of rainfall and on solar radiation is modelled by a Leaf Area Index (LAI). It is one of the parameters in the model that describes land surface vegetation.
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Total leaf area index = (Leaf area index of high vegetation) x (cover in grid box of high vegetation) + (Leaf area index of low vegetation) x (cover in grid box of low vegetation).
Considerations
Users need to be aware of the potential effect of any day-to-day anomalies.
- Widespread storm damage or defoliation will reduce evapotranspiration from model predictions.
- Vegetation growth and decay is climatologically variable but there is currently no interactive biology in the model. Anomalously early extensive vegetation growth in spring or widespread wilting in heatwaves are not modelled.
- Transitory local but significant variations in surface characteristics (e.g. extensive burnt vegetation, seasonal variation in lake extent) are not represented.
- Plant extraction of water and consequent leafiness varies with soil moisture. This can be important especially in relatively dry conditions. In turn this can affect the surface specific humidity.
Additional sources of information
(Note: In older material there may be references to issues that have subsequently been addressed)
Fig2A.1.4.7-1: Example leaf area index (LAI) as shown in the surface parameters charts. The LAI is taken from climatological data. Anomalous weather has not had an effect. Higher values mean more evapotranspiration, and therefore greater fluxes of moisture into the atmosphere. An additional contributor to these moisture fluxes is bare-ground evaporation - this is not represented here. HTESSEL deals with these aspects in more detail. See the current leaf area index chart.
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