Evaporation model (Water Overlay)

Water can evaporate from the hydrological model over time. Multiple forms of evaporation are implemented.

All forms of evaporation can be implicitly activated and deactivated by setting the weather's evaporation rate. If the evaporation factor 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. Multiple periods of evaporation can be defined, and at any specific moment during the simulation an exact evaporation rate is defined by the weather.

For all forms of evaporation, the weather's evaporation rate is used as a base for determining the exact rate of evaporation for that form of evaporation.

Surface evaporation model

Water on the surface can evaporate. The amount is based on the weather's evaporation factor and the grid cell's evaporation factor. These two multiplied result in a evaporation amount per second, which is done for each grid cell individually. Zero evaporation is also allowed.

The evaporation factor of a grid cell is determined during the model initialization phase. Per grid cell the evaporation factor is selected by:

• The grid cell is water: overlay's SURFACE_WATER_EVAPORATION_FACTOR;
• The grid cell is not water:
  • The grid cell has a construction: construction's WATER_EVAPORATION_FACTOR;
  • otherwise: terrain's WATER_EVAPORATION_FACTOR.

Underground evaporation model

Water can evaporate from the underground if the cell has either a construction which allows for underground evaporation, or a surface terrain type which allows for underground evaporation and is unobstructed by a construction. In other words: if a construction is present the construction's properties are used, otherwise the terrain's properties are used.

Underground evaporation can be implicitly activated or deactivated by setting the relevant properties of all terrain types and constructions to appropriate evaporation values. If the relevant properties are set to 0, no underground evaporation will take place. Underground evaporation is also explicitly deactivated when the Underground model is deactivated.

Water can evaporate from the underground via crops and foliage. It can draw water from the underground unsaturated and saturated zones, if their roots reach deep enough and the terrain or construction have a configured evaporation factor. Water is drawn directly from the underground and evaporated, removing it from the hydrological model entirely.

The rate of evaporation is determined by the weather's evaporation rate, and either the construction's WATER_EVAPORATION_FACTOR or the surface terrain's WATER_EVAPORATION_FACTOR.

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.

Water can be evaporated both from the saturated and the unsaturated zones of the underground. The amount of water that can be taken from the saturated and the unsaturated zones is limited by the amount of water in either zone in reach of the roots.