Terrain root depth m (Water Overlay)

Icon	Attribute	Unit	Layer	Range	Description
	ROOT_DEPTH_M	m	Surface		The depth of the roots of the terrain type. This depth is used to determine whether evaporation will occur from the groundwater.

Terrains can be configured with plant-related attributes, similar to constructions configured as crops and foliage, allowing it to draw water from the underground and evaporate it.

Feddes Trapezium

Plants can experience oxygen stress when the groundwater level is too high. The plant roots become saturated so that the plant can no longer perspire. To simulate the oxygen stress, the ROOT_DEPTH_M can also be configured with four values instead of one, which will be interpreted using Feddes transpiration model. In the model, when the groundwater level rises, the perispiration increases. However, at a certain point, the groundwater is too high and the perspiration decreases. Water on the surface can then still evaporate, but the plant cannot perspire anymore.
The sequence for the four values should be defined in order of largest to smallest depth values and are interpreted as a 0-1-1-0 transpiration factor trapezium. File:Feddes trapezium.png

Notes

For plants to evaporate water, both the ROOT_DEPTH_M and the WATER_EVAPORATION_FACTOR must be appropriately configured.
Trees typically have deeper root than crops.
When a construction is present in any given location, the values for evaporation in the underground will overrule any values set by terrain in the same location. To model underground evaporation without a construction, set the attributes of the construction on the applicable terrain type instead.
When there is no construction present on the surface, and the terrain has a ROOT_DEPTH_M of 0, the amount of evaporation which takes place in that location is 0.