Switches Indicators & Gauges

Applications of Rain Gauges

Rain gauges are an important tool for assessing Earth’s water resources. Hydrological data obtained from measurements and essential for effective water resource development and management. Modern networks of hydrological instruments began in Europe and North America in the 18th and 19th centuries, and today consist of stations measuring precipitation, evaporation, soil moisture, ice, water quality, groundwater level and river water levels.

Accurate rainfall predictions are necessary for forecasting short-term climate variability, extreme weather events (such as flash floods), as well as rainfall distribution, possible droughts and analysing climate change patterns. Hydrological networks are also used to assist in pollution protection, water conservation, groundwater protection and inland navigation. Data collection is vital for assessing water quality and quantity, both on the surface and below ground.

Precipitation Analysis

Through using these hydrological networks, information can be collected on things such as the distribution of water across the globe or water availability versus population. For example, Africa has 11% of the world’s available water but 13% of the world’s population, Asia has 60% of the world’s population but only 30% of the world’s water, while South America has only 5% of the world’s population and 26% of the world’s available water (according to a study by UNESCO).

Analysis of world mean precipitation shows large annual totals in the tropics, mid-latitudes and where there are high mountain ranges, according to a joint report by the World Water Assessment Programme (UN). Of course towards the poles and with increasing altitude precipitation is more like to fall as snow. By contrast to these areas of high precipitation, areas furthest from oceans, the polar regions and n the lee of mountains receive little rain. These constitute the world’s deserts and semi-deserts, such as the Australian Simpson and Gibson deserts or the African Sahara Desert. This leads to extreme disparities around the glove, from floods in East & South East Asia and much of South America and central Africa, to drought in northern Africa and much of Australia.

Tipping Bucket Rain Gauge

The tipping bucket rain gauge measures the amount of rainfall in a set period, as well as the character of the rain. It typically consists of a large copper cylinder set into the ground, with a funnel at the top of the cylinder that collects the rain. The precipitation then fall onto one of two small levers which are balanced like a scale. When 0.2mm of rain falls, the lever tips which sends an electrical signal to the recorder. The recorder has a pen on an arm attached to a geared wheel that records movement on a graph. The modern tipping bucket rain gauge usually has a plastic collector balanced over a pivot, which activates a switch when it tips to record and transmitt the amount of precipitation fallen.

The advantage of a tipping bucket rain gauge is that it can tell the character of the rain, whether it is light, medium or heavy, by counting the number of ‘clicks’ in a 10 minute period. A ‘click’ is the sound of the recording arm moving when recording the amount on the graph.

WaterLOG Rain Gauge

The WaterLOG® H-340 is a tipping bucket rain gauge designed to be precise and durable. Constucted of extruded rustproof aluminium and a one-piece cast base, it also features a removable stainless steel funnel screen and no plastic parts. It has a magnetic reed bucket tip sensor, stainless steel or anodized aluminium internal parts, side windows allowing inspection without having to remove the cover, adjustable feet with an internal bulls-eye level, screened bottom ports, optional drain tubes, and precision bucket bearings.

Available from Semrad Pty Ltd, an Australian distributor for high performance level sensors and level controllers, it can be used to accurately measure rainfall, monitor storm water run off or other meteorological functions.

What is a rain gauge?

A gauge is a device for measuring quantities, so a rain gauge measures the amount of liquid precipitation that has fallen over a set period of time. A similar type of gauge is a snow gauge, which measures solid precipitation. A rain gauge is also known as a udometer or a pluviometer.

Basically rain is collected in a cylinder or bucket, then the amount collected is measured to determine the average rainfall in a given time, say over 24 hours. The frequency of readings depend on the collection requirements of the agency, and can be done manually or by an Automatic Weather Station (AWS). In some cases the rain is kept for further testing, such as the determine the level of pollutants in the precipitation.

Rain gauges also several a few limitations to their usefulness. For example, rain gauges can only collect data for a localised area, as levels of precipitation vary across regions. Extreme weather conditions can also hamper efforts to collect rain data, such as conditions with violent winds (e.g. in hurricanes). Even the gauge itself can be unreliable, as drops will invariably stick to the sides or the funnel, making it slightly inaccurate. In very cold conditions, rain can freeze and not allow any subsequent rain to pass through.

Types of Rain Gauges

Most rain gauges are quite simple devices, including graduated cylinders, weighing gauges, tipping bucket gauges and buried pit collectors.

However one of the more advanced gauges is the optical rain gauge. This device has a row of collection funnels, under which each has a laser diode and a phototransistor detector. When a drop of water is formed and falls to the bottom it traverses the path of the laser beam. This scatters the light making it flash, which is then read by the photodetectors and transmitted or recorded.