Measurement of rainfall is done using rain gauges, which collect precipitation and allow the amount to be measured. Non-recording rain gauges, like the commonly used Symons gauge in India, collect rainfall in a vessel that is read daily to determine the amount of precipitation. Recording rain gauges produce a continuous plot of rainfall over time through mechanisms like tipping buckets, weighing the collected water, or tracking a float level. Proper placement and regular maintenance of rain gauges is important for accurate measurement of precipitation.

1. Measurement of
Rainfall
By:-Sulakshya Gaur(121684)

2. Rainfall
 Precipitation is expressed in terms of the depth to which rainfall
water would stand on an area if all the rain water were collected on
it.
 In case of snowfall an equivalent depth of water is used as depth of
precipitation.
 The precipitation is measured in raingauge also called as
pluviometer, ombrometer, hyetometer etc.
 A raingauge consists of a cylindrical vessel assembly kept in open
to collect rain.

3.  A raingauge is affected by its exposure conditions and thus its
setting is important. For setting up a raingauge, the following
considerations are important:
The ground must be level and instrument must present a
horizontal catch surface.
The gauge must be as near the ground as possible to reduce
wind effects but it must be sufficiently high to prevent
splashing.
The instrument must be surrounded by an open fenced area.

4.  Raingauges can be classified into two
categories:
(i) nonrecording gauges and
(ii) recording gauges

5. 1. Nonrecording Gauges:
 The nonrecording gauge used in India is Symons gauge.
 Consists of a circular collecting area of 12.7 cm diameter connected
to the funnel and the rim of the collector is set in a horizontal plane
at a height of 30.5 cm above the ground level.

6.  The funnel discharges the rainfall catch into a receiving vessel
which is housed in a metallic container.
 The water in the receiving vessel is measured by a graduated
measuring glass with an accuracy of 0.1 mm.
 The rainfall is measured at 8:30 a.m. and is recorded as the rainfall
of that day.
 The collecting bottle cannot hold more than 10 cm of rain and thus
in case of heavy rainfall frequent readings must be taken.
 However last reading must be taken at 8:30 a.m. and the sum of
previous readings in the past 24 hours is the rainfall of that day.

7.  Precautions must be taken and raingauges must be inspected
regularly.
 The details of non recording raingauges and measurement of rain
are specified in IS:4986-1968.
 It can also be used to measure snowfall. During snowfall the funnel
and receiving bottle are removed and snow is collected in metallic
container which is then melted and depth of resulting water is
measured.
Antifreeze agents may also be used.
In areas of heavy rainfall special snowgauges are used with storage
pipes.

8. 2. Recording gauges:
These produce a continuous plot of
rainfall against time and are used for
hydrological analysis of storms.
Commonly used recording raingauges:
 Tipping-bucket type
 Weighing bucket type
 Natural-Syphon type

9. (a) Tipping-Bucket type:
 This is a 30.5 cm size raingauge used by US Weather Bureau.
 The catch from the funnel falls onto one of a pair of small buckets.
 These buckets are so balanced that when .25 mm of rainfall collects
in one bucket it tips and brings the other bucket in position and the
water is collected in storage can.
 The tipping actuates an electrically driven pen to plot the intensity of
rainfall with time.
 The water in storage can is measured regularly to give total rainfall.

10. (b) Weighing-Bucket type
 In this the catch empties into a bucket mounted on a weighing
scale.
 The weight of the bucket are recorded with time.
 The mechanism has the capacity to run for as long as one week.
 The instrument gives a plot of accumulated rainfall against time.

11. (c) Natural-Syphon type:
 Also called as float type gauge.
 In this the rainfall collected by a funnel shaped collector is led into a
float chamber causing a float to rise.
 Due to this, a pen attached to the float through a lever records the
elevation of float driven by clockwork mechanism.
 A syphon arrangement empties the float chamber when float
reaches the maximum preset value.
 Its details are prescribed in IS: 5235-1969

12.  The chart shows a rainfall of 58.3 mm in 30h. The
vertical lines correspond to sudden emptying of float by
syphon action.
 It gives a plot of mass curve of rainfall.