Definition of a Rain Gauge
Individuals have tracked and measured rainfall amounts for a variety of reasons. While it is uncertain when the first rain gauge was invented, it is believed the Greeks measured and recorded rainfall amounts as far back as 500 B.C. While the methods were unlike those used today, there was a standardization in place which allowed officials to base crop production and the associated taxes on the annual amount of rainfall received. Does this Spark an idea?
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How A Rain Gauge Works
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The modern rain gauge most commonly used consists of four components: an outer tube, and inner tube, a funnel and a measuring stick. The outer tube, normally 20 cm in diameter and 50 cm in height, holds the inner tube which is 1/10th the size of the outer tube. A funnel at the top of the outer tube directs water into the smaller tube. As rain falls, it is collected by the funnel and fills the smaller tube. Since the collection area is ten times the size of the storage area, measurements in the inner tube are exaggerated by a factor of ten. One inch of water in the tube equals 1/10 of an inch of rainfall. The gauge can read up to two inches of rain. Excess rain is trapped in the outer tube.
Limitations In Accuracy
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The accuracy of a rain gauge is limited. The design of most rain gauges allows them to capture only rain which is falling relatively straight down. In storms, high winds will be driving the rain at sharp angles, sometimes almost in a horizontal pattern. This can prevent the rain gauge from capturing the rain accurately. Spotty summer storms also make accurate rainfall totals difficult. A spot shower can easily dump an inch of rain on the rain gauge while a half mile away or less there was no rain received. Snow and ice can also distort data by blocking the collection tube.
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Types Of Rain Gauges
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Other than the standard rain gauge mentioned above, there are several other models in use. Each of these have their strengths and weaknesses and provide data which helps complete the overall picture. The tipping bucket rain gauge collects rainfall in a bucket and, when the bucket is full, it tips, emptying the water. Each time the bucket is emptied, the time is recorded. The disadvantage to this gauge is that a partially filled bucket will not be counted until it is emptied during the next rainfall event. The advantages is that this gauge allows you to see the intensity of the rain rather than just the total rainfall amount. Another model is the weighing precipitation gauge. This gauge actually weighs the amount of precipitation which falls. These gauges are more expensive and require routine maintenance to keep them in good working order.
Reasons To Record Rainfall
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There are many reasons the accurate collection of rainfall data is important. Agricultural businesses use this information to plan irrigation as well as planting and harvesting schedules. Weather forecasters and storm trackers use this information to help issue flash flood watches and warnings to help protect property and save lives. Engineers use the data to calculate runoff and to help in their design of drainage systems and runoff management. All of these are critical areas depending on accurate and timely information from the rain gauge.
Home Gauges
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Many people like to track rainfall amounts at their homes with a backyard rain gauge. There are many brands available, some strictly functional, while others are very decorative. Whichever type you decide on, make certain it is well away from any overhangs or other items which will block or deflect the rainfall. One of the most interesting gauges is an electronic self emptying bucket gauge. A digital readout located inside your home tells you how much rain you have received and can be programmed to tell you rainfall amounts over the past 24 hours or the total rainfall amount. This device also has an alarm to indicate when it is raining.
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