Contributed by Dustin West

In the latest version of SWMM, there is no option to allow for a seasonally varying CN value which is used to calculate the soil’s maximum moisture storage capacity. A varying CN number for continuous simulations can be important to account for seasonal patterns in soil capacity. For example, CN values can be higher in the late fall to winter/spring seasons and lower in the summer months. In the summer months, dryer conditions as well as plant growth, foliage interception and crop growth are examples for lower CN values.