Leaf area index

Leaf Area Index

The impact of vegetation on interception of rainfall and on solar radiation is modelled by a Leaf Area Index (LAI) taken from climatological data, taking into account seasonality (growing, mature, senescent and dormant phases) of four types of forest and ten types of low vegetation.  Leaf area index is a non-dimensional number representing the square metres of leaf area per square metre of the earth's surface and thus determines also the degree of evapotranspiration.

In IFS the leaf area index varies only with climatology, month by month. Anomalous weather has no effect.

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.

Additional sources of information

(Note: In older material there may be references to issues that have subsequently been addressed)

Fig2.1.17: 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.