NCDC CDO 15 minute precipitation data units not recognized

[michaeltryby]

NCDC CDO 15 minute precipitation data product can be ordered in metric (MM) or standard units (HI, HT). SWMM does not recognize when the units of the supplied data file are in MM it assumes they are either in HI or HT hundred or tenths of an inch respectively. It appears that the rain units attribute for the rain gage selected by the user are being ignored.

This bug is further compounded because the units flag is not being set correctly when ordering data from NCDC CDO. According to the specification 15 Minute Precipitation Data Documentation dated February 2016, the units flag reflects the the units in which the data values are given. This, however, is not the case in practice.

A potential solution to this problem would be to check for the unit flag in the data file. Which currently isn't happening. Another possible solution would be to honor the user indicated units provided in the rain units attribute.

[dickinsonre]

@michaeltryby it would be good if SWMM acknowledged the user defined unit flag in the Raingage property so that a user could use USA unit rainfall in an SI unit model and vice versa.