The SCS/NRCS rainfall distributions are synthetic mass curves that were developed for wide geographic regions based on traditional IDF rainfall data. Roughly speaking, the curves were created by placing the highest rainfall intensity (for a 5-minute duration) at the center of the storm, and then placing the incremental intensity for successively longer (lower intensity) events on alternating sides of the peak. The resulting Type II distribution covers much of the US, although location-specific mass curves can also be developed based on the IDF data for a specific location.
