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Rainfall Probability

rainfall graphs

The two graphs indicate the seasonal probability of specific sized rain
events during the 26 year period from 1971-1997. For example, 50% of the
rain events in Wilmington were 0.2 inches or less. The graphs for
Wilmington and New Bern are quite similar. Both indicate that larger
rain events occur during summer and fall than during the winter or spring.

Such information is useful when planning storm water storage
structures. If plans are made to capture the first inch of rain, what
percentage of the rain events will be controlled? What percentage of the
rain events will exceed the planned storage capacity? How does this
differ with season? It is now 2018, so my “to do” list includes updating the probability plots and seeing if the last 20 years have been different than what is show above.

Dr. Diana Rashash
Area Specialized Agent – Water Quality & Waste Management
North Carolina Cooperative Extension Service
4024 Richlands Hwy.
Jacksonville, NC 28540
Phone: (910)455-5873