Theory question 307
Weather(a) With the aid of a labelled diagram, describe the weather instrument used to measure the amount of rainfall. (b) State three precautions which must be taken when using the instrument described in 7(a). (c) Explain how the instrument described in 7(a) is used to obtain total annual rainfall.
Show the model answer
(a) Rain gauge: a copper or metal cylinder containing a funnel (about 12-20 cm across) that leads rain into a collecting jar or bottle inside; it is sunk partly into the ground with about 30 cm above the surface; a graduated measuring cylinder is used to read the rain collected in mm. Labelled diagram: funnel, outer cylinder, collecting jar, ground level, measuring cylinder.
(b) Place in an open space away from trees and buildings; keep the top about 30 cm above the ground to avoid splashes; sink part of it into the ground to keep it steady and reduce evaporation; read it at the same time every day; keep the funnel clean; protect it from animals.
(c) Measure the rain collected every day (24 hours) and record it; add the daily totals to get the monthly totals; add the twelve monthly totals to obtain the total annual rainfall.
Label the funnel and the measuring cylinder.