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How is rainfall measured?

Rainfall is measured at 08:00 SAST. The rain accumulated in the bucket of the rain gauge is poured into a specially calibrated measuring glass and the millimetre reading is recorded, whereafter the water is discarded. The rainfall measured between 08:00 SAST yesterday and 08:00 SAST today is recorded against yesterdays date on the database. What is meant by 1 mm of rainfall is rainfall equivalent to 1 litre of water in a 1 square meter box with no runoff, infiltration or evaporation.

The South African Weather Service also has a number of electronic rain gauges called Tipping Bucket rain gauges. These gauges consist of a large cylinder set into the ground. At the top of the cylinder is a funnel that collects and channels the precipitation. The precipitation falls into one of the two small buckets which are balanced side by side. As soon as it starts raining one of the buckets fills with water. After an amount equal to 0.2 mm falls into the bucket the bucket tips and an electrical signal is sent to a recorder. The next bucket is then in place to collect precipitation. The two buckets seesaw up and down collecting and recording the rainfall. The instrument is thus able to record not only the amount of rain that falls but when it started and stopped raining.

Different rainfall intensities are described in the image below.

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