How is Precipitation and Rainfall Measured and How do Rain Gauges Work?
From the lack of rain during times of drought to the dangers of floods when we receive too much of it, rainfall impacts everybody. In addition to this, precipitation is one of the most critical components of the Earth's hydrological cycle. Everyday rain gauges and weather radar are used to measure, record, and transmit precipitation data to weather stations around the country. Meteorologists and other weather professionals analyze this data and use it to issue informed statements to the public, government officials, and the news outlets. Rainfall data is also frequently utilized by gardeners, farmers, and engineers to plan and prepare for future events. So just how exactly is this valuable piece of information measured and reported everyday?
Types of Rain Gauges
The most common form of rainfall measurement occurs with a rain gauge. Rain gauges are devices that directly measure the depth of precipitation that has fallen at a specific location. There are four basic types of rain gauges that are currently in use all across the United States; the rainfall scale, the float gauge, the tipping bucket gauge, and the simple graduated cylinder or container.
Rainfall Measurement Factoid:
Did you know that any container that has a flat bottom and straight sides can be used to measure the depth of rainfall? An empty coffee can or even a cake pan used in conjunction with a ruler can be used to measure the rainfall depth at any particular location. All containers that have a flat bottom and straight sides will report the same amount of rainfall (if put in the same location) because the volume of water landing in it is directly proportional to the area of the container's opening. Even though the volume of rainfall in each container will be different, the depth will actually be the same. An inch of rain is exactly that, water that is one inch deep. One inch of rainfall equals 4.7 gallons of water per square yard or 22,650 gallons of water per acre!
Weighing Rain Gauge
The first type of rain gauge is the rainfall scale (also known as a weighing precipitation gauge). In this device, a scale actually weighs the amount of water that has fallen into it and converts this information to a depth. Rainfall scales offer the most accurate form of measurement, even during high intensity storms. These gauges also offer the ability to automatically record and send rainfall data directly to weather stations. The downsides to this type of gauge include their high initial cost and the high amount of maintenance and calibration required to keep them functioning. Weighing scales certainly have their advantages but have somewhat fallen out of use in recent years because of the costs associated with using them.
The second type of rain gauge in use in America is the float gauge. This gauge utilizes a float mechanism that rises as the depth of water in it increases. This gauge also has the ability to automatically record depth information over a period of time and send it to a weather station. Float gauges have also fallen out of use in recent years giving rise to the tipping-bucket gauges.
The third type of rain gauge that people use are graduated cylinders or container gauges. This low-tech device has to be manually read and dumped after every storm. It is also the least accurate of all of the rainfall measurement methods. Because of these limitations, these types of gauges are only typically used by homeowners and farmers interested in the rain falling at their particular property. Meteorologists and weather professionals prefer gauges that are more accurate and have the ability to report data automatically.
Tipping Bucket Gauge
The fourth and most common type of rain gauge that is in use in America is the tipping-bucket gauge. In a tipping bucket gauge, the rain falls into a large opening that funnels water into a narrow tube. The tube then outlets the water onto one of two buckets that are balanced opposite of each other (like a see-saw). Each bucket can typically hold 1/100th or 0.01 of an inch. When the bucket fills up, it tips and dumps out the water allowing the opposing bucket to fill up. The gauge counts the number of times that the bucket is tipped during a storm to calculate the amount of rain that has fallen. A tipping bucket gauge electronically records the rainfall data and sends it to the weather station for processing. The benefits of this type of gauge is that is very accurate and requires very little maintenance compared to the other methods of rainfall measurement.
Radar Estimated Precipitation
Sometimes using a weather radar system can be a good way to obtain precipitation depth data. A weather radar is a type of radar that is capable of detecting the motion of rain droplets in addition to the intensity of the precipitation in the atmosphere. This data can be analyzed to determine the structure and nature of storms as well as their potential to cause flooding and other disasters. Weather radar is much less accurate than direct measurement but provides an easy means of estimating rainfall depths in areas that are far away from gauges. However, if calibrated using actual rain gauge data, radar measurement can prove to be a very useful and accurate way to obtain real-time rainfall data.
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