Evaporation model (Water Overlay)

Water can evaporate from the hydrological model over time. Multiple forms of evaporation are implemented, namely surface and underground evaporation.

Both forms of evaporation can be configured directly by setting the weather's evaporation rate. If the evaporation rate is set to 0, no evaporation will take place in any form.

The weather's evaporation rate is defined as a period during which a certain rate of evaporation will take place, similar to rainfall. Multiple periods of evaporation can be defined, and at any specific moment during the simulation an exact evaporation rate is defined by the weather.

Per form of evaporation, the weather's evaporation rate is used as a base for determining the exact amount of evaporation per timestep.

Surface evaporation model

Water situated on the surface is conceptually able to evaporate. The amount is based on the weather's evaporation rate and the overlay's SURFACE_WATER_EVAPORATION_FACTOR. These two multiplied result in a evaporation amount per second. The water on the surface of each individual cell is then subject to the calculated rate of evaporation.

Underground evaporation model

Water can evaporate from the underground if the cell's surface meets either of the following criteria:

• A construction on the surface
  • The construction has a non-zero WATER_EVAPORATION_FACTOR.
  • The construction has a non-zero ROOT_DEPTH_M.
• No construction on the surface
  • The surface terrain type has a non-zero WATER_EVAPORATION_FACTOR.
  • The surface terrain type has a non-zero ROOT_DEPTH_M.

In other words: if a construction is present the construction's properties are used, otherwise the terrain's properties are used.

Conceptually, water can evaporate from the underground via crops and foliage. These can draw water from the unsaturated and saturated zones in the underground, if their roots reach deep enough and the terrain or construction have a positive evaporation factor. Water is drawn from the underground and evaporated into the air, effectively removing it from the hydrological model. Water for evaporation can only be drawn from sections of the underground which are within reach of the roots, as defined by the root depth.

Evaporation can only take place if the roots of the terrain or construction can reach underground water. The depth the roots can reach is defined by either the construction's ROOT_DEPTH_M or the surface terrain's ROOT_DEPTH_M.

The underground evaporation can be configured directly by changing the terrain type's WATER_EVAPORATION_FACTOR and construction 's WATER_EVAPORATION_FACTOR. If these attributes are set to 0, no underground evaporation will take place.

Similar to the surface evaporation, the rate of underground evaporation is also determined by the weather definition's evaporation rate. Multiplying the weather's evaporation rate and the evaporation factor of the construction or terrain (as applicable) gives the actual evaporation rate for the underground.

Underground evaporation first draws water from the saturated region and then from the unsaturated region. If, according to the calculated evaporation rate, a sufficient amount of water can evaporate from the saturated zone, no water will evaporate from the unsaturated zone. Otherwise, all water in the saturated zone which is in reach of the roots of the construction or terrain (as applicable) is evaporated, and the remainder of the amount of water which should evaporate according to the evaporation rate is evaporated from the unsaturated zone. The sum of evaporation in the saturated zone and the unsaturated zone will never exceed the calculated evaporation rate.

Related formulas

• Surface evaporation formula
• Underground evaporation formula

Related models

• Surface model
• Underground model

Notes

• An evaporation rate of zero is allowed, but a negative evaporation rate is not. Negative evaporation rate is treated as zero.
• Underground evaporation will only take place when the underground model not active.

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