Rain and Rain Gauge: Working Principles and DIY
We are deep into the monsoons, which brings increased rainfall and provides the perfect opportunity to measure and assess rainwater collection. This period of heightened precipitation allows us to accurately gauge how much rain is falling and how effectively we are capturing it from our rooftops. By measuring the rainfall now, we can optimize our rainwater harvesting systems and better understand their efficiency. This data is crucial for managing water resources and planning for future needs. Taking measurements during the monsoon ensures that we capture representative data, making it an ideal time to evaluate and enhance our rainwater collection strategies.
A rain gauge is a meteorological device used to measure the amount of rainfall over a specific period and area. It features a collection container placed in an open space. The instrument gauges precipitation by the height of the water collected in the container over time, with measurements expressed in millimeters. Rain gauges are valuable for tracking changes in precipitation over time, maintaining landscapes and understanding planting times. It also helps in communicating rainfall data to larger communities so that we can have collective understanding of rainfall for that context.
Types of Rain Gauge:
The three major types of rain gauges are the standard gauge, tipping bucket gauge, and weighing gauge. How are they different from each other? Based on the way they are set up and and based on how they deliver data. But largely, the function of the rain gauge remains the same.
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The recording of rainfall using the standard or funnel rain gauge is generally done manually. These gauges work by catching the falling rain in a funnel-shaped collector that is attached to a measuring tube. The area of the collector is 10 times that of the tube; thus, the rain gauge works by magnifying the liquid by a factor of 10.
Magnifying the rain in this way allows precise measurements down to a one-hundredth of a mm. Amounts that exceed the tube capacity are caught in the outer shell of the gauge, allowing the recorder to pour out the liquid in the tube and fill it back up if needed.
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The operation of a tipping bucket rain gauge is quite different from the standard gauge. The receiving funnel leads to one of two small buckets. Filling of one bucket occurs at one-hundredth of a mm. The result is a “tipping” of the liquid into the outer shell of the gauge, triggering the second bucket to take its place.
The process then repeats itself, allowing for precise measurement of rainfall intensity and amount. This gauge has become standard for wireless weather stations.
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The universal weighing rain gauge is optimal for climatology use. This is because of a vacuum that accounts for the effects of wind, allowing more rain to enter the gauge. These gauges are very precise in measuring rainfall intensity as the weighing mechanism at the bottom of the collector can be used to measure depth and time simultaneously. Recording is carried out much in the same way as the older versions of the tipping bucket gauges.
Site Selection For Rain Gauge:
When choosing a site for installing a rain gauge, consider the following:
The location should be on flat, level ground; avoid hilltops, slopes, or uneven terrain.
The site must be open and unobstructed.
Objects near the rain gauge should be positioned at least twice their height away.
The gauge should be protected from persistent wind.
Other meteorological instruments and site fencing should follow the distance guideline in point 3.
The location should be easily accessible.
The rain gauge must be perfectly vertical.
At least 10% of the rain gauge stations in any area should have self-recording capabilities.
Regular visits by the observer are necessary to ensure the gauge is properly maintained and ready for accurate measurements.
DIY Rain Gauge:
STEP 1: gather the following materials: 1 plastic bottle (1 litre), 1 pair of scissors, and tape(duct tape, transparent tape, etc).
STEP 2: cut the plastic bottle at the top just before it starts to narrow as shown in the image below
STEP 3: use this cutout part as a funnel to be placed in the plastic bottle
STEP 4: Usually bottoms of water bottles are never flat, therefore draw a line near the base just before it starts to narrow. Now cut a strip of tape and place it on the side of your gauge. With the help of a marker and a ruler, mark off every millimeter until you reach the top of the gauge
STEP 5: Pour pebbles and water up to the line drawn at the bottom of the gauge, this will help give some stability to the rain gauge.
STEP 6: your rain gauge is now ready to be used. Place your rain gauge outside on a leveled and flat surface. It is best to place the rain gauge at a height where there are no obstructions such as branches or people walking by.
Calculating the amount of rainwater one can harvest from their roof
Step 1: Determine Local Rainfall
To estimate the potential amount of rainwater you can collect monthly or annually, first find out the average rainfall in your area using a rain gauge.
Step 2: Measure Your Roof's Surface Area
Calculate the total surface area of the roof(s) in square meters that will be used to collect rainwater.
Step 3: Calculate Harvestable Rainwater
To find out how much rainwater you can harvest, multiply the average rainfall (in millimeters) by the roof surface area (in square meters). This will give you the volume of water you can expect to collect in liters
Traditional rain gauges and weather stations at an individual scale across any city or landscape can help in understanding localized weather phenomena and help us interact with the weather more efficiently. Coffee farms in Coorg have traditionally maintained rainfall data to extend their cultivation knowledge. One can also purchase raingauges online.