SWMM Climatology

SWMM Climatology objects are database items used in SWMM networks to define climate-related values for:

• Evaporation - This may occur for standing water on subcatchment surfaces, for subsurface water in groundwater aquifers, for water travelling through open channels, and for water held in storage units. Evaporation rates can be specified as:
  • a single constant value
  • a set of monthly average values

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

  Note that the evaporation rates supplied to SWMM are potential rates. The actual amount of water evaporated will depend on the amount of water available.

• Wind speed - these are specified as monthly averages and are only used for snow melt calculations.
• Adjustments are modifications that can be applied to the temperature, evaporation rate, and rainfall that ICM would otherwise use at each time step of a simulation. Separate sets of adjustments that vary periodically by month of the year can be assigned to these variables. They provide a simple way to examine the effects of future climate change without having to modify the original time series.

  A set of monthly adjustments can also be applied to the hydraulic conductivity used in computing rainfall infiltration on pervious land surfaces and exfiltration from storage nodes and conduits. These can reflect the increase of hydraulic conductivity with increasing temperature or the effect that seasonal changes in land surface conditions, such as frozen ground, can have on infiltration capacity. Similarly, a soil recovery rate, where infiltration capacity is recovered during periods with no precipitation, can be adjusted by a fixed amount on a monthly basis to account for seasonal variation in such factors as evaporation rates and groundwater levels.

SWMM Climatology items are viewed and edited using the SWMM Climatology Editor.

If a run includes a rainfall event that defines the time varying data for evaporation, then this will be used in a simulation rather than the values specified for a SWMM Climatology object which is included in the same run. However, if no evaporation data is included in the rainfall event, then the evaporation values in the applicable climatology object will be used for the simulation.

Any adjustments defined in the climatology object included in a run will be applied to the applicable SWMM network during a simulation.