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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:

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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.  Evaporation and evapotranspiration remains at maximum.

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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

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