What is IFD?
The abbreviation IFD stands for Intensity-Frequency-Duration; it refers to statistics on rainfall. In order to explain what it is, we must first define some terms about rainfall. We usually think of rainfall as being of a certain DEPTH (measured in mm). But for completeness, we also need to specify the length of time over which the rainfall occurred: one year – in the case of annual rainfall; one month (for many climate purposes); or so many days, hours or minutes. This period of time over which the rain is measured is called the DURATION. So rain is well described in terms of a depth of rainfall over a certain duration. To compare the severity of different rainfall events, we might compare several rainfalls measured over one hour. For instance, we might be interested in the highest one-hour rainfall during a calendar year at a certain location. And going one step further, a civil engineer designing a drain intended to fail no more frequently than once every ten years (on average) migh
