Variations in rainfall measurement

Robin Leaney - Engineering and Water Supply Department SA , 02 October, 1990

Of all the components of the hydrological cycle, the element of rain is the most commonly measured. It would
appear to be a straightforward procedure to catch rain as it falls and these simple measurements have been made for
more than 2000 years. The first recorded mention of rainfall measurement came from India as early as 400 BC.
The first rain gauges were used in Korea in the 1400s AD and 200 years later, in England, Sir Christopher Wren
invented the self recording rain gauge.

However, meteorologists and hydrologists appreciate that making an acceptable rainfall measurement is not as easy as
it may first appear. It is not physically possible to catch all the rainfall over a drainage basin; the precipitation
over the area can only be sampled by rain gauges. The measurements are made at several selected points
representative of the area and values of the total volume (m3) or equivalent a real depth (mm) over the catchment
are calculated later.

Many investigations into the problems of rainfall measurement were carried out in Europe and the United
States in the late 1800s and early 1900s. such are the problems in obtaining representative samples of the
precipitation reaching the ground that, over the years, a comprehensive set of rules has evolved. The principal aim
of these rules is to ensure that all measurements are comparable and consistent. All observers are recommended to
use standard instruments installed uniformly in representative locations and to adopt regular observational

Perhaps it is time that these rules, standards and procedures be reviewed and that considerable fundamental
re- thinking take place . We are living in a time of rapid technological change. Should we broaden our scope and
concentrate on variety and quantity rather than accuracy?