User's Manual

The world has been mapped into Rain Regions and historical data gathered on
the probability of rain at a given density (millimeters of rain per hour). The ITU
has created maps
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to help visualize this rain patterns, as in Figure 10-9.
In the United States, the 150 mm/hr rain rate happens only 0.001% of the time,
and that is in Florida (Region N). A percentage of 0.001% is approximately equal
to 5 minutes a year.
Figure 10-9: Rain Regions for the Americas (ITU-R P.837-1).
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ITU-R P837-1. This older version of the standard uses alphabetical regions. The newer P837-2
maps by probability zones.
ARCXtend manual, August 2003 10-10