How to measure rainfall

Rainfall is a natural phenomenon that is highly fascinating to see. In addition, measuring rainfall is sometimes a challenging endeavour because of the substantial degree to which it fluctuates throughout the course of time and location. Therefore, when it comes to measuring rain, the most significant challenge is variability. The accuracy, on the other hand, may be improved by using precise rainfall measuring instruments such as rain gauges.

In this article, we will discuss the types of rainfall, as well as the different kinds of rain gauges and how to use them to accurately measure rain.

 

How to measure rainfall: Major types of rainfall 

The majority of precipitation that occurs comes in the form of rain. There are three primary classifications of rainfall. The explanations for each are as follows:

Convectional rainfall

A combination of condensation and evaporation results in this kind of rainfall, which is most common in tropical regions. It takes place when the temperature at the surface of the earth rises above that of its surroundings. Rainfall caused by convection occurs when the atmosphere is unstable or has a high moisture content. When the temperature increases, the air that is warmer than the surrounding air rises. This process is known as evaporation. When air reaches a particular altitude, it begins to lose heat and expands as a result. This leads to the formation of clouds. Cumulus clouds are the name given to the clouds that are created. Convectional rainfall occurs most often everywhere in the world.

Relief / Orographic rainfall

When clouds form in the vicinity of a mountain range, the mountains get relief rainfall. Clouds form above the mountains and then go on. The temperature of the air drops as it travels farther from its source. In turn, this causes the formation of orographic clouds, which ultimately result in rainfall. Such rainfall is carried over the mountains by the wind and often falls on the windward side. Scattered rainfall across a relatively small section of the ridge is known as spillover. Relief rainfall results in flooding and storms because of the asymmetrical rainfall. The fast nature of this downpour makes it impossible to stop.

Frontal / Cyclonic rainfall

Rain that falls as a result of a cyclone is often referred to as frontal rainfall since it typically occurs along a cyclone’s front. Rainfall associated with fronts is caused by the collision of warm air and cold air. Warm air has a lower density than cold air. Therefore, heated air will ascend to a higher level than cooler air. When the air rises high enough, it becomes saturated, and this results in intense rainfall. Strong winds, torrential rain, big storms, landfalls, and even tornadoes are all results of cyclones. The nature of a rain front makes it capable of wreaking havoc on a large scale. Additionally, it leads to extensive soil erosion.

 

How to measure rainfall? 

Rain gauges, also known as pluviometers, are instruments that are used for measuring rainfall. The meteorological department has used this particular instrument for a very long time. Although rain gauges may provide a rough estimate of how much precipitation has fallen, there is no universally accepted method for calculating rainfall totals. Each rain gauge has its own unique system for collecting and analysing precipitation data. Thus, it is important to identify the method of measurement used by each rain gauge.

See also: What is universal testing machine and how it is used?

 

How to measure rainfall with different rain gauges 

Non-recording rain gauge

Source: Wikipedia 

 

The Symons Rain Gauge is a kind of non-recording rain gauge that simply provides the total quantity of rainfall for a specific time period. It is equipped with a funnel and a bottle receiver that is cylindrical in shape. Both the receiver and the top of the funnel have a diameter of around 127 millimetres. The receiver’s neck accommodates the funnel, and the complete assembly rests in a metal housing equipped with appropriate packs. The base of the housing is broader, measuring about 210 millimetres, to improve its stability. This gauge can calculate the total rainfall for a given time period using a calibrated measuring jar.

It is important to notice that the funnel, which is usually held at an elevated position to avoid splashing, serves as a collector for the raindrops just before they hit the ground. The graduation, rather than the gauge itself, is the measuring tool that is being used here. On a regular day, measurements are taken at 8:30 in the morning.

Measuring cylinder rain gauge

Source: Pinterest 

 

This is the most basic recording version of the rain gauge. A big cylinder with graded markings and a funnel make up its components. For the purpose of tapping or collecting raindrops, the funnel is positioned above the measurement cylinder. It is possible to do immediate measurements of the water while the jar is being filled.

The cylinder in this gauge does not function in the same way as a regular cylinder. Here, you must immediately read the data without draining the cylinder’s contents beforehand.

Tipping bucket rain gauge

This gauge consists of a cylinder with a funnel at its end and two buckets stacked on top of each other in a horizontal orientation. Rainwater may be collected using a funnel and channelled into a cylinder that ultimately empties into a bucket. If the bucket is filled to a specific depth with water, suppose 0.03 centimetres, it will tilt and move aside to make room for the following bucket. In order to calculate how much water is collected, the system receives a signal based on the number of nozzles.

Weighing bucket rain gauge

This rain gauge consists of a cylinder that is balanced on top of an electronic scale. The amount of water that enters the cylinder causes a rise in its weight, which offers an indirect indication of rainfall. These scales may be linked to charts that track the total quantity of rainfall over a certain period of time.

Floating rain gauge

Source: Pinterest 

 

This measuring device consists of a funnel that leads to a chamber that floats. When there is more water in the funnel, the float will begin to rise. The float is equipped with a stylus that follows the path of raindrops falling onto a revolving drum and records the information. The mechanism of the lever controls the operation of the stylus.

Optical rain gauge

Source: Pinterest 

 

These types of rain gauges measure rain using lasers and light. The quantity of light that passes through the gap between the laser and the optical detector is diminished when raindrops fall through the gap. The variation in the brightness of the light is what gives the impression that there is rain falling.

 

How to measure rainfall at home 

Source: Pinterest 

 

A plastic bottle or any other cylindrical container would do well as a rain gauge if you wish to monitor rainfall levels in your backyard.  Continue with the steps as they are given below.

1. If you take a plastic container and use scissors to remove the bottle’s neck, you may turn it into a container in the shape of a cylinder. It’s possible that the bottom of the container isn’t completely flat.
2. After inverting it, the cut-out top should be placed onto the container. It will function as a funnel while also preventing the loss of liquid due to evaporation.
3. The container should be filled with water to the point where it completely covers the uneven area at the bottom. Make a note of the water level.
4. The reading should be taken after 24 hours, during which time the container should be positioned in an open area far from any obstructions, including a tree or a barrier.
5. Using a ruler, do the calculation necessary to determine the amount of water that has risen. The amount of precipitation, measured in millimetres or inches, is equal to the increase in water level.
6. Spend the next week reading the measurements first thing in the morning.
7. After each reading, ensure that the container is empty, and then go to step 3.
8. To get the weekly average amount of precipitation, sum up all of the data and then divide the total by 7.

 

FAQs:

What's the most precise method for calculating rainfall?

Putting a rain bucket with a specified diameter on a scale (often one that is 12 or 24 inches in circumference) is the method that yields the most accurate readings when used to measure rainfall. The weight of the container is subtracted from the total mass of the rain by the scale.

What precautions must be used while measuring rainfall?

The rain gauge must be positioned in an open area, away from any nearby trees or pipes, before any attempts are made to measure rainfall. All sides of a gauge must be exposed to the weather, the gauge's inside should be maintained clean, and the gauge must be emptied daily at precisely the same time.

What are the restrictions on using a rain gauge?

The use of rain gauges is not without its caveats and restrictions. For instance, due to the strong winds that might be present during a hurricane, it may be very difficult to obtain measurements of the amount of rain that has fallen. In addition, rain gauges may only be used for the purpose of determining the amount of rainfall within a certain region.

Why do we measure rainfall in millimetres?

The reason rainfall is recorded in millimetres is that a typical rainshower drops an amount of water that corresponds to these units.

Does a rain gauge's shape make a difference?

According to studies, a rain gauge that has a typical design will cause the wind around it to be disrupted and will cause the airflow to pick up speed. This causes a rise in turbulence over the tip of the funnel, which in turn results in a reduction in the quantity of precipitation that is captured by the measuring device.