Ground evaporation formula (Water Overlay)

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Ground evaporation is calculated per cell.

For all ground evaporation calculation, the ground water depth at time t is used.

Feddes oxygen stress factor:

Feddes saturated zone root update factor:

Max potential evaporation:

Evaporation unsaturated:

Potential evaporation saturated:

Evaporation saturated zone:

Evaporation total is the sum of evaporation in the saturated and unsaturated zone:

where

= the datum height of the surface of cell c, set by the elevation or a Terrain elevation prequel.
= the ground water level (datum height) at time t.
= the depth of the ground water level, which is equal to the column height of the unsaturated zone at time t.
= the transpiration factor of the buildings (plants) on the surface, or the surface terrain's transpiration factor if none present.
= the evaporation rate of the weather at time t
= the calculated feddes oxygen stress factor, calculated using the 3rd and 4th root depths and the feddes trapezium interpolation model and the ground water depth.
= the calculated feddes saturated zone root update factor, calculated using the 1st and 2nd root depths and the feddes trapezium interpolation model and the ground water depth.
= The ground bottom distance of the cell c, defined by a Bottom distance prequel or a general GROUND_BOTTOM_DISTANCE_M of the Water Overlay.
= the column height of the saturated zone covered by the roots
= the nth root depth value.
= the amount of water in the unsaturated zone.
= the potential max evaporation
= the evaporation in the unsaturated zone
= the potential evaporation in the saturated zone
= The WATER_STORAGE_PERCENTAGE of the ground terrain type, used here as a fraction.
= the evaporation in the saturated zone
= the total evaporation from the ground.


Related

The following topics are related to this formula.

Formulas
Groundwater level formula (Water Overlay)
Models
Ground model (Water Overlay)
Evaporation model (Water Overlay)