Theory question 203
Weather(a) With the aid of labelled diagrams, describe the instruments used to measure rainfall. (b) Explain how the instruments are used to obtain total annual rainfall. (c) State any two precautions to be taken in the use of the instruments.
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(a) Rain gauge: a metal cylinder (about 12.7 cm or 20 cm wide) sunk into the ground with about 30 cm above the surface; a funnel at the top leads rain into a glass bottle/collector inside; a graduated measuring cylinder (in mm) is used to measure the water. Labelled diagram showing funnel, outer case, bottle, ground level and measuring jar.
(b) Rain collected is poured into the measuring cylinder and read daily at a fixed time; daily amounts are added to give monthly totals; the 12 monthly totals are added to give the total annual rainfall.
(c) Place it in an open space away from trees and buildings (at least twice their height away); top rim about 30 cm above ground to avoid splashing; keep it firmly fixed and level; read at the same time each day; read at eye level; check for leaks and empty after reading; protect from animals.
Name the parts on the diagram.