Rain Gauge

A rain gauge is an instrument used in meteorology to measure the amount of rainfall during a given period. Used by the Greeks as early as 500 BC to measure precipitation, this device that was once only used by professionals now has its place in the home. Weather amateurs love using it to fine-tune their observations, while gardeners can use it to plan their gardening activities and watering.

How does a rain gauge work?

The purpose of a rain gauge is to provide a measurement of the quantity (by volume or mass) of precipitation - i.e. of rain but also snow and hail - that falls in a given area over a given period. This quantity is expressed either in millimetres or relative to the surface area, in litres per m2.

Rain gauges traditionally take the form of a funnel, also called a collecting device, which is used to collect rainwater during precipitation and direct it either into a kind of graduated cylinder that needs to be manually emptied afterwards in the case of the most basic models, or into a more elaborate tipping bucket system that measures the water that falls before draining it. The bucket system enables continuous measurement without the user having to empty the water between every reading and prevents measurement errors caused by evaporation. These days, most rain gauges feature electronic sensors that save the device's data and remotely send it to a weather station.

To obtain reliable measurements on the level of ground precipitation, it's best to place a rain gauge on a flat surface in an open area where all of the water falling from the sky can be collected by the collecting device. It's usually recommended to place the instrument between 50 cm and 2 m off the ground. This makes it easy to install and to read the measurements in the case of a graduated cylinder. Placing the instrument too high up or on a sloping surface could cause reading errors. It's also necessary to be aware of errors caused by the presence of an obstacle nearby the collector: if it's windy, the rate could appear to be lower and the volume collected could be less than the average on the ground. Discover all our products

What type of rain gauge should you choose?

There are many different types of rain gauge, all of which work differently and have different levels of accuracy. The WMO (World Meteorological Organisation) recommends an average measuring accuracy of 0.2 mm.

You should first choose a rain gauge based on its capture method, either manual or electronic. The first type means you need to regularly empty the recipient, which might be a problem if there's heavy rain or snow, or alternatively if hot weather makes evaporation more likely. Stagnation can also cause a problem in terms of the accuracy of the height observed. Although bucket capture is tried and tested, enthusiasts of traditional methods enjoy using a manual instrument.

The electronic method can handle heavier rainfall, as the funnel is gradually emptied so that it can handle a continuous flow of precipitation, and the sensors are more accurate. Often linked to a weather station, the system sends the data directly to the station. Stations therefore have the advantage of connecting several accessories and sensors, meaning they can read the temperature, the temperature felt, wind speed and intensity, and combine information on rain and snow with other factors that influence the weather and the actual temperature.

The benefits of a smart weather station

Rain gauges linked to smart weather gauges are even more effective. These devices allow you to save and view readings remotely, give average readings of the information collected, highlight trends based on a data history, etc. You can even access your readings on your computer or smartphone using a dedicated app. Because users can pool their figures, this allows for an even more extensive analysis.

Some stations also convert precipitation measurements into recommendations, for example for watering your garden, which might be useful if it's hot and there hasn't been much rainfall. If you have a home automation setup, the sprinkler system can also be automatically started.

Whichever method is used, graduated recipient or bucket, adjust the size of your module's collecting device to the amount of rain liable to fall in your local area. If you choose an electronic model, make sure it has a good battery life and that the range between the various modules is sufficient to cover the distance between the water capture areas and the analysis areas.

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