Content

• To step
• Part 1 of 2: Making your rain gauge
• Part 2 of 2: Measuring rainfall
• Tips

Being able to measure the amount of rain fallen is important for many different professional sectors, so it's not surprising that the rain gauge was one of the first weather-related tools our ancestors invented. They are believed to have been used in India as early as 2,000 years ago. Rain gauge measurements are used by farmers to make choices about planting, harvesting and irrigating crops. They are also used by engineers to design well-functioning sewers, bridges and other structures. Although most professional rainfall measuring devices today are electronic, anyone can create their own rain gauge to measure rainfall themselves.

To step

Part 1 of 2: Making your rain gauge

1. Find a clear, cylindrical container. The cylinder can be plastic or glass and must be at least 12 inches long. The shape is also important: if the top is wider or narrower than the bottom, you will have a lot more measuring and calculating work.
   • It does not matter how wide the holder is, as long as it is the same width everywhere. As the volume of the container increases - for example, from a Coke can to a bucket - the surface area that collects rain also increases. As a result, every centimeter of rainfall is measured in the same way by cylinders of different sizes.
2. Make a container. If you don't have a cylinder handy, you can make a great rain gauge with an empty 2-liter lemonade bottle and a little work. Cut the top 10 inches off the bottle with scissors. Don't worry about the uneven bottom of the bottle. We will solve that in the next step.
3. Weight your meter with stones. Since rain often goes hand in hand with wind, it is wise to make your gauge sturdy so that it can stand up in a storm. Fill the bottom with pebbles or marbles, but don't go higher than a few centimeters. After this, partially fill your container with water so that you have an even starting point for your bowl. Your weights take up space, and of course we don't want to include them in the rain.
   • Stones, pebbles, marbles: anything is fine as long as it is small and relatively heavy, and it does not absorb water.
   • If you are using a lemonade bottle for your gauge, make sure that the entire bottom is submerged so that you have an even starting point for the bowl.
   • You can also put your meter in a larger sturdy container, such as a bucket or flower pot, to keep it stable.
4. Draw a scale on your holder. You can do this with a waterproof marker. Hold a ruler or tape measure near your bottle, and line up the 0 with the water level of your meter. The zero point of your scale must start at this water level.
   • If you've opted for a flower pot or bucket instead of pebbles, you won't have water in your meter yet. In this case, the bottom of your container is the zero point.
5. Place your meter in the open air, on a flat surface. The surface must be smooth to prevent your meter from falling over. Make sure there are no obstructions above your meter, such as a tree or eaves, as these will interfere with the measurements.

Part 2 of 2: Measuring rainfall

1. Check your meter every day. To determine how much rain has fallen in the last 24 hours, you need to check every 24 hours! Read the gauge by looking at the water level, with your eyes level with the water level. The water surface will be slightly curved; this is the meniscus, which is formed by the surface tension of the water hitting the walls. You have to measure the bottom point of the water level.
   • It is important that you check your meter every day, even if there has been no rain. You can lose water through evaporation, and water can mysteriously be added without rain clouds, for example from nearby water sprinklers. In this case, you need to find a new place for your meter.
2. Visualize the fallen rain with a graph. For example, you can create a graph with 7 days and 20 centimeters, putting the days of the week on the x-axis and 0 to 20 centimeters on the y-axis. After you put a dot in the correct spot for each day, you can connect the dots with a ruler and see the changes in rainfall for that week.
3. Empty your rain gauge. It is best to empty your rain gauge after each measurement. Keep the same pebbles or marbles in your meter, and refill the container with water to the zero point on your scale. If you do add or remove pebbles, make sure the water is always down to zero before you reset your meter.
4. Calculate the mean. Once you have collected data for a month, you can analyze it and find trends in rainfall. By adding up the rainfall from all 7 days in a week and then dividing by 7, you get the average daily rainfall for that week. You can also do this for months (and even years if you are very committed).
   • The formula for finding the mean is easy to apply. The average is the sum of all items (in this case the rainfall for each day, week or month) divided by the number of items (in this case the number of days, weeks or months you measured). If you look for the average rainfall over 4 weeks, with weekly numbers of 51 cm, 30 cm, 15 cm and 63 cm, then the average weekly rainfall is 51 + 30 + 15 + 63 = 159 (the sum of all items) / 4 (the number of weeks) = 39.75 cm.

Tips

1. When it snows, you can measure the snowfall with your meter if you let it melt first - as long as your meter is not snowed under. However, the snowfall measured as rainfall does not have a constant relationship with the depth of the snow, so don't jump to conclusions. Two feet of snow can have very different amounts of water.