Page History

...

The characteristics of each grid box are updated through the forecast period (e.g. model snowfall might increase the area or depth of snow cover within the grid-box; model rainfall might increase soil moisture rather than be removed by run-off).  The areal extent of each land surface "tile" type (listed above) can vary in a rapid, interactive way during the model run, as rain falls then evaporates or as snow accumulates then melts, etc.  The slope and aspect of orography within each grid-box (e.g. south-facing, steepness) is not taken into account and HTESSEL may consequently under- or over-estimate solar heating and runoff.

...

For each soil type and location there is a pre-defined value of the ability to hold moisture and this is used to assess the impact of model rainfall.  The HTESSEL system includes allowance for water capture from precipitation, dew fall, and snow-melt.  At the same time, there are infiltration and run-off schemes that take account of soil texture and the standard deviation of sub-grid scale orography.

...

Evaporation from bare soil depends on the soil moisture alone.

See also Section 9.2.1.3 Errors associated with soil moisture.

Evapotranspiration

Plant evapotranspiration efficiency varies between the permanent wilting point (PWP) and field capacity (CAP). Evapotranspiration efficiency:

...

• the expected air temperature and moisture structure in the lowest 2 m together with energy fluxes (from HTESSEL) and an analysis of observed screen level (2 m) humidities.
• satellite soil moisture data from the ASCAT sensor on the MetOp satellites.
• data from the Soil Moisture and Ocean Salinity satellite mission (SMOS) is used for operational monitoring (see Fig2A.1.4.5-2).

...

Grid point data is plotted for Europe.  Elsewhere, for (most) other parts of the world, soil moisture is interpolated from surrounding grids points.  Field capacity, saturation, wilting point etc. depend on the soil type so can consequently be affected.  Users should check nearby soil moisture before accepting misleading soil moisture actual and forecast data.

See also Section 9.2.1.3 Errors associated with soil moisture.

Contrasting examples of surface and soil water budgets

...

• Actual soil characteristics can vary widely within a grid box.  Users and forecasters should take into account the peculiarities of a location when interpreting model output.
• The assigned average soil type for a grid box is not necessarily representative of an individual location.
• Runoff can be up to 30% of rainfall in complex orography or mountainous regions.
• Soil moisture increments have less impact on 2m temperature and 2m humidity (and vice versa) since 14 May 2025.
• Recycling of moisture by evaporation from surface often has an impact on maintaining cyclones over the dessert.
• Availability of water in the soil for plant uptake allows plant roots to better extract water, especially in relatively dry conditions.  Evapotranspiration can affect the surface specific humidity.
• Impacts of errors associated with soil moisture. 

Additional sources of information

...

• Read more on Soil Moisture and Evapotranspiration Efficiency with example chart.

(FUG Associated associated with Cy50r1)Links OK Read OK Diags OK