Page History

...

• soil moisture variables for the top layer (Layer 1,  7cm deep),  This layer has the greatest impact on the atmosphere.  It is 7cm deep.  
• average soil moisture variables for the top three layers (Layer 1, 2 and 3,  1 metre deep).  This is derived by summing the contributions from Layer 1 (0-7cm), Layer 2 (7-28cm depth) and Layer 3 (28-100cm depth), weighted according to thickness.  Layers 2 and 3 (and indeed 4) have an impact on the atmosphere via:
  • plants with deeper roots.
  • moisture transfer between soil layers.  This can operate both:
    • upwards by capillary action.
    • downwards under gravity.

Soil moisture charts

Image Removed

Fig2.1.4.5-3: Examples of Soil Moisture at T+00 and T+192 DT 00UTC 06 March 2023.  

Example soil moisture chart VT 00UTC 06 March 2023 showing moisture in soil level 1, the surface layer.  The legend shows:

...

Note the change in soil moisture over France from ~60% of field capacity (greens) to above 60% of saturation (blues). This is largely due to rain exceeding evaporation in these areas during the forecast period.  Conversely, parts of northern Morocco, northern Algeria and northern Tunisia have become a little drier.

See the current soil moisture chart.  Select "Layer 1 2 3" from the drop down menu for the average moisture in the top metre of the earth.

Image Added

Fig2.1.4.5-4: Relationship between soil moisture fraction and evaporation efficiency.

Evaporation efficiency varies according to the soil moisture content.  

• Soil moisture SM < Permanent wilting point PWP.  Dry or arid ground.  Living vegetation cannot be sustained.  No evaporation or evapotranspiration.
• Permanent wilting point PWP

...

• < soil moisture SM < field capacity CAP.

...

•  The percentage evapotranspiration efficiency increases with additional soil moisture.  Efficiency reaches the maximum at field capacity. 

• Capacity CAP < Saturation SAT.  Soil moisture super-saturation.

...

Note the change in soil moisture over France from ~60% of field capacity (greens) to above 60% of saturation (blues). This is largely due to rain exceeding evaporation in these areas during the forecast period.  Conversely, parts of northern Morocco, northern Algeria and northern Tunisia have become a little drier.

...

•  Evaporation and evapotranspiration remains at maximum.

Colour scale used for the soil moisture charts.  

• Sandy shades: Soil moisture SM < Permanent wilting point PWP.  Living vegetation cannot be sustained. Values show soil moisture as a percentage of the permanent wilting point value.
• Yellow/Green shades: Permanent wilting point PWP < soil moisture SM < field capacity CAP.  Values show soil moisture as a percentage of the field capacity value.  
• Blue shades: Capacity CAP < Saturation SAT.  Soil moisture super-saturation. Dark blue (>90%) suggests flooding (in the model).

Rarely in moist areas there are some soil moisture plots (except over Europe) indicating the soil is exceptionally dry.

...