Geoscience Reference
In-Depth Information
In some situations where the gauge density is high enough, it may also be possible to
create contour maps of composite correlation coefficient in which the correlation
fields for each gauge are superimposed. Figure 14.12b shows an example of a contour
map of composite correlation coefficient for this same area of Queensland showing
correlated bands of precipitation inland away from the coast separated by 40-45 km.
Important points in this chapter
Mapping precipitation
: drawing isohyets of precipitation involves esti-
mating the location of points with the required precipitation value between
pairs of gauge measurements then drawing
smoothed
isohyets through these
points.
●
Area mean precipitation
: is the value calculated as a weighted mean of
available precipitation observations, with weighting assigned in one of
several possible ways including using (a) the
Isohyetal
, (b) the
Triangle
, and
(c) the
Theissen
methods, although the Theissen method is often preferred
and all methods tend to produce similar results, especially if applied over a
long period.
●
Spatial organization
: storms tend to be organized in pseudo-elliptical or
linear groups, with individual storms elliptical in shape, more elongated
when larger, and with the
rate of change
in intensity increasing toward the
middle of the storm.
●
Design storms
: statistical analysis of observed storms results in the definition
of regional relationships between peak storm intensity and area-average
precipitation called
areal reduction factors
which are used in hydrological
design and which vary with storm duration and/or storm return period.
●
Probable maximum precipitation (PMP)
: the hypothetical estimate for a
region of the greatest possible precipitation that might occur in extreme
atmospheric conditions over a specified area and period of time: it is variously
calculated but may be an overestimate relative to observed maximum
precipitation rates.
●
Spatial correlation
: spatial characteristics of the atmospheric mechanisms
involved in precipitation release in a region can be revealed by analysis of the
correlation between observations from a rain gauge network (see text).
●
References
Hanson, E.M., Schreiner, L.C. & Miller, J.F. (1982) Application of probable maximum pre-
cipitation estimates - United States east of the 105 meridian.
Hydrometeorological Report
52
, National Weather Service, NOAA, Washington, DC.
Niemczynowicz, J. (1982) Areal intensity-duration-frequency curves for short-term rainfall
events in Lund.
Nordic Hydrology
,
13
, 193-204.
