It’s raining; it’s pouring

You can find out how much rainfall there is in your area with this simple instrument.

August 06, 2021 10:01 am | Updated 10:01 am IST

How much rain has come down?

How much rain has come down?

Have you ever wondered how much rain falls during a drizzle or a thunderstorm? Or during the rainy season or even the whole year? Let’s look at why it is important to measure rainfall.

For societies like ours that are entirely dependent on rainfall for agriculture, drinking water and other needs, keeping a record obviously helps. In the past, for example, the amount of rainfall helped kings decide on how to tax the farmers! Good rains, high taxes; bad rains … well, if the king was kind then low taxes!

It is believed that people have kept records of rain since the time of the ancient Greeks and that the first measurements were made with the help of a rain gauge. In India, this instrument was made in the fourth century BCE. While there are many mentions of rain gauges in history, the first standardised rain gauge is dated to around 600 years ago and credited to a Korean king.

How it works

Anyone can make a standard rain gauge. All you need is a cylindrical tin/steel box. The cylinder should have millimetres marked on the side and a funnel of an equal diameter on top. The rain is collected in the cylinder via the funnel and the water level is measured using the scale. While quite effective and simple, this gauge has some accuracy issues.

Anyone can make a simple rain guage

Anyone can make a simple rain guage

To tackle this, the funnel rain gauge was developed. It consists of a funnel-shaped collector and a measuring tube. The area of the collector is 10 times that of the tube; so the reading is magnified by a factor of 10. This measuring tube is suitably marked to accommodate this magnification. Measurement in both these types is done manually and the protocol is to measure at 8.30 a.m. daily.

Many different types of rain gauges have been developed over time. Automatic rain gauge systems were originally developed to collect rainfall data at remote locations, where logistics prevented regular visits. These are now widely used for their accuracy and also because they can give live readings that are very useful in the era of climate change.

But this doesn’t mean that the simplest standard and funnel rain gauges are outdated. They are still actively used across the world, including by students to measure rainfall and contribute to an overall understanding of rainfall patterns

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