How Do We Measure Rainfall? A Fun DIY Guide

You're watching the weather forecast and the presenter says that we're expecting 0.6 inches of rain today.

But what does 0.6 inches of rain mean?

And how can they measure rainfall so precisely?

As it turns out, anyone can measure rainfall with the right tools and by following a few simple steps.

Read on to find out how to measure rainfall, including tools to use, the math behind it, and a simple guide to setting up your own rain gauge at home.

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Why Do We Measure Rainfall?

From preventing or mitigating floods to protecting our crops, measuring rainfall can help keep lives and livelihoods safe.

• Predicting Weather: Measuring rainfall helps predict weather patterns such as storms and heavy rain, keeping us informed about upcoming weather changes and long-term climate trends.
• Agriculture: Farmers rely on rainfall data to schedule irrigation (how much they water their crops) and decide when to plant crops, ensuring healthy growth and good harvests.
• Water Resource Management: Monitoring rainfall helps in managing reservoirs, lakes, and groundwater levels, crucial for city water supply, industry, and ecosystems.
• Flood Prevention: By measuring rainfall, we can predict and prepare for floods, keeping communities safe by giving them time to get ready and protect themselves.

What Units Do We Use to Measure Rainfall?

We use units like inches or millimeters to quantify how much rain has fallen over a certain time period, usually in a day (24h), a week, month, or season.

These units tell us how high the water would rise if it stayed on a flat surface without soaking in or running off to a nearby river, lake, or sea.

So, when we say we’re expecting 0.6 inches of rainfall today, that means that the amount of rain that would fall within the next 24h could rise to 0.6 inches if it stayed on surface.

Some of you may ask:

Why do we use units of length (inches and millimeters) instead of units of volume (pints or liters) to measure rainfall?

The reason is simple:

Measuring the height (or depth) of accumulated rain is easier than determining the volume. Once you know the height, you can calculate the volume of rain that has fallen over a certain area.

How Do Experts Measure Rainfall?

Experts use special tools to measure rainfall accurately. Here are some of them:

Rain Gauges

A rain gauge is a simple instrument that col lects rain in a graduated cylinder, which has markings to show the amount of rainfall.

The standard rain gauge meteorologists use is a cylinder of 8-inch (about 203 mm) in diameter.

There are different types of rain gauges:

• Standard Rain Gauge: A clear, cylindrical container with a funnel that directs rainwater into a measuring tube. You can read the amount of rain directly from the tube.
• Tipping Bucket Rain Gauge: This gauge has a small bucket that tips over when it fills with a certain amount of water. Each tip is recorded, and the total number of tips is used to calculate the rainfall amount.
• Weighing Rain Gauge: This gauge measures the weight of the collected water and converts it to a rainfall amount.

Weather Station Tools

Automated weather stations have rain gauges and other tools to measure temperature, humidity, wind speed, and more.

They use advanced tools and technology to collect data all the time, interpret it, and send it to meteorologists.

Weather stations use advanced tools to collect, interpret, and even predict rainfall and other data.

Radar

Weather radar uses radio waves to find rain. It sends out waves that bounce off raindrops and come back.

By checking how strong the waves are and where they come from, radar can tell how much it's raining and where.

Satellites

Satellites in space have special sensors that look at clouds and rain from above. They help scientists see how much rain is falling and where, all over the world.

Anyone Can Do It! Here's How You Can Measure Rainfall

You don't need fancy equipment to measure rainfall.

You can create your own rainfall gauge to measure and calculate rainfall at your own home.

Here's a fun DIY project to get you started!

To create your own rain gauge, you need:

• A clear plastic or glass cylindrical container, like a jar or a 2-liter bottle with the top cut off. It doesn’t matter how wide the container is, as long as it’s the same diameter all the way through.
• A ruler
• A marker
• A flat, open area outside

You can turn a simple glass jar into a rain gauge.

Steps:

• Find a Good Spot: Choose an open area away from surrounding buildings and trees. They can block rain or cause splashes, leading to inaccurate measurements. Make sure the ground where you place your container is flat, so the rainwater collects evenly.
• Measure and Mark the Container: Use the ruler to mark inches on the side of your container. Start from the bottom and go up. Use the marker to draw lines and label the measurements.
• Wait for Rain: Place your container outside when the rain starts.
• Measure the Rainfall: Check the water level in your container every day at the same time and write it down in a notebook or on a chart.

To make a chart, mark the days of the week along the bottom line (x-axis) and inches of rain along the vertical line (y-axis). Place a dot where each day's rainfall measurement intersects on the chart. Use a ruler to connect the dots and see how rainfall varies throughout the week.

When you collect the measurements for multiple days, usually a week or a month, you can calculate the average rainfall for that period.

Just add up all the measurements you've recorded and divide the total by how many days you measured the rainfall.

Great job!

You've measured rainfall like a real meteorologist. With simple tools and steps, you've learned to track rainfall and understand your local weather.

What Math Do We Use to Measure Rainfall?

Believe it or not, we use 3^rd grade math to calculate rainfall.

As we’ve seen in the earlier example, we measure rainfall by reading the water levels our rain gauge collects each day and we calculate the average rainfall for a specific period.

What do we need to calculate average rainfall?

• Decide on the period you want to track – usually one week or one month
• Add up the rainfall levels for each day during that period, whether it rained or not
• Divide the sum of rainfall levels with the number of days

And there you have it! You have successfully determined the average rainfall.

Let’s try with an example.

Imagine we have a rain gauge in our backyard, and we’ve read the rainfall levels it collected each day at the same time. The measurements are:

Now we want to calculate the average rainfall for the week.

First, we add up all the measurements we’ve gathered:

2 + 0.5 + 0 + 0.8 + 1 + 0.5 + 0.1 = 4.9 inches

Then, we divide the sum of measurements with the number of days:

4.9 ÷ 7 = 0.7

There we have it!

The average rainfall for the week was 0.7 inches.

How to Calculate Rainfall Volume

Calculating rainfall volume gives us a more precise measure of how much water has fallen over a specific area.

Unlike for rainfall levels, we use gallons or liters to express rainfall volume.

How do we calculate it?

By using the simple formula for volume: the area of the base x height of the figure.

How to Calculate Volumes

In our case, the base can be our yard, while the height is the average level of rainfall we calculated using our rain gauge.

So, to calculate the amount of rainfall, we:

• Measure the Rainfall Levels: We track the rain levels using our rain gauge daily over a certain period, usually a week or a month.
• Determine the Area: We specify the area for which we want to measure the rainfall volume. We measure this area in square feet (ft²) or square meters (m²).
• Calculate the Volume: We multiply the average rainfall level by the area to get the volume of rain.
  

Here’s what the calculation would look like:

We will use our previous example where the average rainfall was 0.7 inches in one week.

To determine the average amount of rain that’s fallen over our yard in one week, for example, we will multiply the average rainfall with the area of our yard.

Let’s say our yard is a perfect square measuring 4,000 sq. ft., or 576,000 sq. In.

To get the volume, we will multiply the average rainfall level with the area of our yard:

0.7 in × 576,000 in² = 403,200,000 in³

This means that over the past week, 403,200,000 cubic inches (1,745,454 gallons) of rain fell over a yard.

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