Weather elements

 Rainfall 

How to measure rainfall (precipitation)

Rainfall is a form of  precipitation and is measured in millimeters (mm) using a rain gauge. Rain gauges are made out of copper or plastic because these materials do not rust or corroded. Rain gauges can be set up in two different ways: they can either be mounted on or against a pole or they can be planted in the soil.

       Figure 1.1 shows a rain gauge mounted on a  pole 

All rain gauges must be set up away from buildings or trees, because these can either prevent rain from falling into the rain gauge or add extra water into the gauge. Both situations will cause an inaccurate reading.

How to measure the amount of water in the rain gauge

Water from the rain gauge is poured into a measuring cylinder. The measuring cylinder should be placed on a flat surface, take the reading while keeping the cylinder horizontal and leveled with your eyes. Remember to take the reading at the bottom of the meniscus.

*Meniscus is the area of water on the surface that is touching the sides of the measuring cylinder.

Rainfall is recorded by using a bar graph 

Figure 1.2 shows rainfall recording in 2013 and 30 years ago 

Calculating rainfall averages:

To calculate the rainfall average for a month,  the figures for every day must be added and then the total must be divided by the number of days in that month. 

example:

A week has 7 days ,if it has rained for 5 days, you add all the rainfall figures and divide the answer by 5.

5mm + 10mm + 0mm + 15mm + 5mm = 35mm

35mm ÷ 5( number of days it has rained)

=7mm ( average rainfall)

Look at figure 1.3

Figure 1.3 shows recorded rainfall for a week between two towns

A zero (0) indicates that there was some precipitation (rainfall) although it was not enough to be measured in a rain gauge. A dash (-) indicates that there was no precipitation at all on that day. If the rainfall figure for a day is indicated with a (0), that day must be added to the number of days with which you are going to divide. If the rainfall is indicated with a (-) then that day must not be included in your calculations.