IDF to Incremental depth 1

You should not need to do this.

For Chicago you are probably going to be using a Type II storm.

You didn't say but you need to decide what duration storm you will use, or are required to use. Usually that is a 24 hour storm but you need to know that.

Next you need to know what Annual Exceedence Probability storm, or storms, you will use. 1%, 10% 25%, 0.5% ?
Then you need to know the total rainfall for the durations and AEPs of interest to you. These can be found on Isospluvial maps published by NOAA. They can be downloaded at NOAA's website. Google it.

As for software you can use the NRCS ( formerly SCS ) free program WINTR-55, or HydroCad, or Hydraflow Hydrographs, or, SWMM ( free) or SMADA or HEC-HMS to generate the hydrographs for your design storm(s).

good luck

I think you're asking about a "Chicago-style" rainfall distribution. This is a general technique for defining an SCS-type rainfall distribution using IDF coefficients. This can be used anywhere, not just Chicago.

This is one of the many rainfall formats supported by HydroCAD. For details please see

The IDF should actually give you a somewhat more local hyetograph than the blanket SCS Type II. Now I wholeheartedly agree with the earlier and more useful posts (especially RWF7347 since it is unlikely that you are going to do better than the National Weather Service
), but why not select you time off the IDF compute a depth and then distribute like a type II (It is something like 40% at the peak of a 24 hour period.) Also if you are using TR55 graphical you do even need to trouble with that.

And if you have ATLAS 14 data why even bother ruining all that databy altering it to a type II.