I am trying to generate an Intensity-Duration-Frequency (IDF) curve using 6-hourly precipitation data. These curves are used to estimate the return period for a rain event with a specific intensity (in mm/hr) and duration. The event duration is on the x-axis which typically ranges from a few minutes to 24 hours, and the rainfall intensity on the y-axis. You get sets of curves, one for each return period. A frequent issue while trying to generate IDF curves from global climate models is the lack of sub-daily output because it is expensive to write out rainfall very frequently (say, 1 hour) in a global climate model that runs 100 years.
I currently have 6-hourly data from a global climate model. The literature is filled with references to 'empirical adjustment factors' that essentially generate sub-daily data from lower frequencies. But I am finding it a bit hard to figure out what exactly are these factors. Here is an example of what I mean, the link does not even bother to mention what adjustment factors are being used or provide a reference. Is there a reference that clearly states what are these factors? Any help is much appreciated.