Geoscience Reference
In-Depth Information
13
Precipitation
Analysis in Time
Introduction
Analysis of variations in precipitation with time at a specified location is undertaken
in many ways, the nature of which is determined by their purpose. This chapter
provides an overview of some of the more important of these purpose-driven
analyses and the associated approaches used. One major reason for analysing
historical precipitation records is to characterize the
precipitation climatology
of a
specific geographical location in present day climate. This is expressed in terms of
the normal expectation for the amount, intensity, and timing of precipitation.
A second motivation for precipitation analysis is to discern the existence (or
otherwise) of any long term trends or periodic oscillations through time that may
be occurring within the local precipitation climatology. Sometimes analysis has
been made of the relationship between rainfall amount and duration, or of the
within-storm timing of rainfall with a view to identifying the
system signature
of a
storm to identify the atmospheric mechanism that caused it.
The most practical motivation for sophisticated statistical analyses of
precipitation records is to provide the basis for the design of infrastructure or water
management systems. Such analyses might, for example, seek to aid agricultural
management by estimating the likelihood of severe drought, or the 'reliability' of
receiving precipitation above the minimum value required to grow a crop. Or on
the basis of past observations, they might seek to define the frequency and
magnitude of extreme events and associated flood discharge to aid the design of
drainage systems.
The descriptions of analyses of precipitation in time that follow are written in
general terms without defining the source of the precipitation measurements.
However, because the analysis methods described generally assume the existence
of long precipitation data records, in practice such analyses are usually made using
gauge data.
