[FR] What are IDF Curves? Intense precipitation events can deliver large amounts of rain over short periods of time. This rain, as well as related flooding, can overwhelm storm drains, flood basements, wash out bridges and roads, and trigger landslides. To reduce the risk of these impacts, engineers, hydrologists, planners and other decision makers rely on accurate information about extreme rainfall events. IDF curves are one important source of this information. Three main elements are described in IDF curves: Duration: The period of time of interest. Typical IDF curves include extreme precipitation durations ranging from 5 minutes to 24 hours. Intensity: The average rainfall rate over the specific duration of interest, in units such as mm/h. Frequency: To plan for extreme events of a specified duration and intensity, it matters how often such events occur. This is often described as a return period, which is defined as how often, on average, the event is expected to occur. Frequency can also be thought of in terms of probability or likelihood. For example, an event with a 1-in-20 year return period will occur on average once every 20 years, and therefore has a 1-in-20, or 5%, chance of occurring each year.
Intense precipitation events can deliver large amounts of rain over short periods of time. This rain, as well as related flooding, can overwhelm storm drains, flood basements, wash out bridges and roads, and trigger landslides. To reduce the risk of these impacts, engineers, hydrologists, planners and other decision makers rely on accurate information about extreme rainfall events. IDF curves are one important source of this information.
Three main elements are described in IDF curves:
Duration: The period of time of interest. Typical IDF curves include extreme precipitation durations ranging from 5 minutes to 24 hours.
Intensity: The average rainfall rate over the specific duration of interest, in units such as mm/h.
Frequency: To plan for extreme events of a specified duration and intensity, it matters how often such events occur.
This is often described as a return period, which is defined as how often, on average, the event is expected to occur. Frequency can also be thought of in terms of probability or likelihood. For example, an event with a 1-in-20 year return period will occur on average once every 20 years, and therefore has a 1-in-20, or 5%, chance of occurring each year.
