Geoscience Reference
In-Depth Information
Figure 14.7
Point area precipitation relationships for Lund, Sweden by return period. (From Niemczynowicz, 1982,
published with permission.)
Design storms and areal reduction factors
The general relationship found in many parts of the world between the area-
average precipitation in a storm, the storm area, and the peak intensity at its focus
is used as the basis for defining and calibrating
design storms
for climatological
regions. To define design storms, observations of individual precipitation events
gathered from a dense gauge network in the region are analyzed to specify the
average shape of the intensity distribution when normalized to the peak intensity
in each storm. Because storms with more persistent precipitation tend to have
greater storm area and also tend to be rarer, the relationships which describe the
precipitation intensity distribution relative to the peak intensity are different for
classes of observed storms when subdivided by storm duration and/or storm
return period. Hence, the results of such analyses are expressed in terms of the
relationship between the peak storm precipitation and the area-average
precipitation for storms subdivided either on the basis of return period (Fig. 14.7)
or on the basis of duration (Fig. 14.8).
