Rain Gauge


The finished rain gauge.

A rain gauge is another really easy tool to make as part of a weather station. As our world experiences Global Climate Change, comparing local rainfall to that of previous years gives first-hand evidence to assess the impact of changing weather patterns. Although one year a trend does not make, it is still interesting to track rainfall and determine if it does vary from predicted rainfall.

If you are in the United States, the following website has average monthly rainfalls for different cities across the country. http://average-rainfall.weatherdb.com/ . I would imagine similar sites exist for other countries. This site also gives one the ability to compare the rainfall in two different cities.

Supplies
Straight edged clear plastic bottle (liter soda, olive oil, etc.)

Scissors or utility knife
Plaster of Paris
Polymer resin
Glue gun and glue
Ruler (with inches and centimeters) or computer
Permanent marker
Optional: Square board double the width of your bottle

Directions:

  1. Remove the labels from the bottle. There is a product on the market called Googon that helps with that. I used an olive oil bottle and had the hardest time getting the label glue off. Googon was the only way I could remove it.

    Olive oil container with its top cut off.

    Olive oil container with its top cut off.

  2. Cut the top off the bottle, just at the point where the sides start going straight, so that when the top is turned upside down, it looks like a funnel. If you notice in my bottle, there is a strainer on the inside of the cap at the top. I am going to leave that on. My thinking is that it will help to keep bugs from falling in during the summer.
  3. If the edges are jagged, re-cut so they are smooth.
  4. Cut a very small notch in the top edge of the bottom of the bottle. Due to the perspective of the picture, my notch looks bigger than it actually is. The notch should be about an inch deep and half an inch wide. The purpose of the notch is empty the gauge of rain. If you put the notch on the corner of the bottle, instead of the middle of the side, it may be easier to pour out water when needed.
  5. If the bottom of the bottle is uneven, fill it with plaster of Paris, made according to the directions on the package. Filling the bottom with plaster also adds weight and will prevent it from tipping over in windy weather. If the bottom of your container is uneven, you will not get accurate readings for total rainfall.
  6. Let the plaster dry at least 12 hours, then coat it with a plastic polymer resin, making the plaster impervious to water.

    Plaster added to the make the bottom flat, and a layer of polymer resin over that to make it impervious.

    Plaster added to make the bottom flat, and a layer of polymer resin over that to make it impervious.

  7. If your rain gauge still feels too light, like a gust of wind would tip it over, use the glue gun to glue it to a wider board.
  8. Glue the cut off top of the container onto the bottom, but turn the top upside down so it is like a funnel that extends into the bottle. It is not advisable to leave the top open, as water will evaporate. For instance, if you want to get an idea of how much rain falls over an extended period, with the top inserted upside down, water will evaporate much more slowly. Actually, it will probably evaporate at the same rate, but having a smaller opening means it will be trapped, and it will have a harder time escaping out of the bottle. You will not get a completely accurate number, but it will be closer to the actual number than if the top were not attached.
  9. Using the ruler, mark ¼ increments on the side of the bottle, starting at the bottom, just above the polymer and plaster base,  and working up. On the other side of the bottle, do the same, but use centimeters instead of inches. (There are very few left in the world still using inches, and this is another way to familiarize children with the two measurements, especially as they relate to each other.) The other option is to print out a paper ruler from the internet (http://www.vendian.org/mncharity/dir3/paper_rulers/UnstableURL/rulers_cm_in_decimal.pdf ) and secure it to your plastic bottle with tape, covering  the entire surface of the ruler. I actually had some leftover resin that I painted over the ruler. The resin should work just as well as the tape.
  10. Leave your gauge away from the house and out from any overhang, like a tree or roof. This should help you to get more accurate readings.
  11. Use the enclosed chart to graph your monthly rainfall compared to your area’s monthly rainfall. You will need to add labels to the axis, and a chart table. I am getting more computer savvy, but not enough to figure out how to import an excel chart with all the formatting it should have. You will find the chart at the bottom of the page.
  12. Challenge your child with the following questions/activities:
  • How do your readings compare to those recorded for your area?
  • Predict what the rainfall will be for the coming month.
  • What month will have the most rain?
  • What month will have the least rain?

chartraingauge

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