If the explicit solver is used, user can include evaporation loss calculation for open channels. The calculation is carried out if user specifies evaporation data from Components > SWMM Extensions > Climatology > Evaporation. The solver calculates the evaporation flow loss based on the dynamic water area of the open channel and the global evaporation data.

From the evaporation data editor, the evaporation rates can be stated as:

• a single constant value
• a set of monthly average values
• a user-defined time series of daily values
• values computed from the daily temperatures contained in an external climate file
• daily values read from an external climate file

Note that these represent potential rates. The actual amount of water evaporated will depend on the amount available.

If rates are read directly from a climate file, then a set of monthly pan coefficients should also be supplied to convert the pan evaporation data to free water-surface values.

An option is also available to allow evaporation only during periods with no precipitation.