This is called its return period or frequency of occurrence. The intensity of a storm can be predicted for any return period and storm duration at St. Louis using Fig. These charts were prepared by making a statistical analysis of point rainfall data. They are periodically revised as more data become available. Rainfall Characteristics Rainfall characteristics affect the amount of runoff which occurs, the severity of erosion possible in various parts of the country, and our dependency on irrigation for crop growth.
Rainfall occurs when moisture in the atmosphere condenses into drops.
Raindrops occur about in any shape up to approximately 9 mm mean diameter after which they tend to break up. Intensity and Duration. These are usually inversely related, i.e., high intensity storms are likely to be of short duration and low intensity storms can have a long duration. Intensity and Area. Intensity and Drop Size.