Climate Change Adjustment vs. Rational Method Frequency Factor

Product(s): SewerGEMS, SewerCAD, StormCAD, CivilStorm
Version(s): CONNECT Edition
Area: Modeling

Problem

What is the difference between the Climate Change Adjustment factor and the Rational Method Frequency Factor ?

Solution

While both can be used to increase catchment outflow, the difference is that one applies to the base depth or intensity of the storm event (to account for climate change influence) while the other applies to the Rational C (to account for reduced capacity for land to absorb rainfall for higher intensity events).

The Rational Method Frequency Factor is a calculation option that enables users to adjust the Rational C of all catchments as seen here. For example a multiplier of 1.1 would cause all catchment Rational C values to be 10% higher than the user-entered values.

       

The Climate Change Adjustment is an attribute of the rainfall alternative (as defined in the Global Storm Events dialog or from the New Storm Events Scenario wizard) that enables users to adjust the base depth (for time-depth storms) or base intensity (for IDF or time-intensity storms) of storm events. For example a constant climate change adjustment of 10% for an IDF storm means the intensity will be 10% higher than the values in the IDF curve.

Also, when using the EPA SWMM runoff method, the "SWMM" option enables users to access the standard SWMM style monthly climate adjustments multipliers via the climatology dialog.

See Also

New Storm Event Scenarios Wizard

Applying a C adjustment factor to different return events

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