How to Make a Hyetograph in Excel

A hyetograph is a powerful way to visualize rainfall, showing you exactly how its intensity changes over the course of a storm. This article provides a clear, step-by-step guide to creating a professional-looking hyetograph directly within Microsoft Excel, complete with a cumulative rainfall curve for even deeper analysis.

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What is a Hyetograph and Why is it Useful?

In simple terms, a hyetograph is a bar chart that displays the distribution of rainfall over time. The horizontal axis represents time intervals (like minutes or hours), and the vertical axis represents the rainfall intensity or depth for each interval. The result is a visual profile of a storm, allowing you to quickly identify periods of peak rainfall and lulls in precipitation.

This is incredibly valuable in fields like:

• Hydrology and Civil Engineering: To design drainage systems, sewers, culverts, and other stormwater infrastructure that can handle peak flow rates during intense storms.
• Environmental Science: To study erosion patterns and the runoff of pollutants, which often spike during periods of heavy rain.
• Agriculture: To understand how irrigation and rainfall patterns affect soil moisture and a crop's water supply.

By transforming raw rainfall data into an intuitive chart, a hyetograph makes complex information easy to understand at a glance.

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Step 1: Prepare Your Rainfall Data

Before you can make the chart, you need clean, organized data. All you need are two columns: one for time and one for rainfall. The rainfall can be measured either as total depth (e.g., inches or millimeters that fell within that interval) or as intensity (e.g., inches/hour or mm/hour).

For this tutorial, let's use a sample dataset from a 6-hour storm, with rainfall recorded hourly.

Open a new Excel sheet and set up your data like this:

1. In cell A1, type Time (Hour). In cell B1, type Rainfall Depth (mm).
2. Populate the columns with your data. The time column should represent the end of the time interval.

Here is some sample data you can use to follow along:

Column A (Time) | Column B (Rainfall Depth) 1 | 5 2 | 12 3 | 25 4 | 18 5 | 8 6 | 3

It's critical that your data is consistent. If your time intervals are hourly, make sure every row represents one hour. If they are 15-minute intervals, stick to that throughout. Inconsistent intervals will distort your chart and lead to incorrect analysis.

Step 2: Create the Basic Hyetograph Chart

With your data neatly organized, you can now create the chart. Excel makes this part simple.

1. Select Your Data: Click and drag your cursor to highlight all the cells containing your data, including the headers. In our example, you would select cells A1 through B7.
2. Insert a Column Chart: Navigate to the Insert tab on Excel’s ribbon. In the Charts section, click on the "Insert Column or Bar Chart" icon. From the dropdown menu, select the first option under 2-D Column, which is Clustered Column.

Excel will instantly generate a basic column chart on your worksheet. You’ll see time intervals on the x-axis and rainfall depth on the y-axis. This is the skeleton of your hyetograph, but it needs a bit of formatting to look like a proper one.

Step 3: Format the Chart into a Proper Hyetograph

A true hyetograph doesn't have gaps between the bars, because time is continuous. Fixing this is the key formatting step, along with updating labels to make the chart clear and professional.

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Remove the Bar Gaps

The bars in a hyetograph should touch to represent the continuous nature of the time intervals.

1. Right-click on any of the blue data bars in your chart. A context menu will appear.
2. Select Format Data Series... from the menu. This will open a "Format Data Series" pane on the right side of your Excel window.
3. Under "Series Options," look for the Gap Width slider.
4. Change the value from whatever it is (e.g., 219%) down to 0%.

As soon as you change the gap width to zero, you'll see the bars expand to touch each other, instantly giving your chart the signature look of a hyetograph. You might also want to add borders to the bars to help distinguish between them. In the same formatting pane, click on the Fill & Line tab (the paint bucket icon), select Border, and choose a solid line in a color like black or dark grey.

Add Axis Titles and a Chart Title

An unlabeled chart is meaningless. You need to explicitly state what each axis represents.

1. Click anywhere on your chart to select it. Three buttons will appear on the top right corner of the chart.
2. Click the plus icon (+), labeled "Chart Elements."
3. Check the boxes for Axis Titles and Chart Title (if it isn't already checked).
4. Click on the newly appeared "Axis Title" boxes on your chart to edit them. Set the horizontal (X) axis title to Time (hours) and the vertical (Y) axis title to Rainfall Depth (mm).
5. Click on the Chart Title at the top and give it a descriptive name, like Hyetograph of storm on [Date].

Step 4: Add a Cumulative Rainfall Curve (Mass Curve)

Often, a hyetograph is paired with a cumulative rainfall line, also known as a mass curve. This S-shaped line shows the total accumulated rainfall over the entire storm duration. Displaying both together provides a more complete picture of the storm's characteristics. This involves adding data, adding a second axis, and combining chart types.

Calculate Cumulative Rainfall

First, you need to calculate the cumulative data to plot.

1. In your data table, label cell C1 as Cumulative Rainfall (mm).
2. In cell C2, enter the formula =B2 to start the accumulation.
3. In cell C3, enter the formula =C2+B3. This takes the previous cumulative total and adds the current interval's rainfall.
4. Drag the fill handle from C3 down to C7 (or your last data row) to fill the formula. Your table will now have a third column showing the running total of rainfall.

Add the Mass Curve to the Chart

Now, let's get that new data onto the chart.

1. Right-click anywhere on the chart area and choose Select Data... from the menu.
2. In the "Select Data Source" dialog box, under "Legend Entries (Series)," click the Add button.
3. A new "Edit Series" dialog box will appear:
4. Click OK twice to insert the new series.

You’ll now see a second set of bars (probably in orange). Don't worry — we're about to change them into a line.

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Create a Combo Chart with a Secondary Axis

The final step is to combine the bar and line chart types and put the cumulative rainfall data on its own axis since its scale (total depth) is different from the intensity scale.

1. Right-click on the orange bars representing the cumulative data series, and select Change Series Chart Type....
2. The "Change Chart Type" dialog opens. Ensure your chart types are set as follows:
3. Click OK.

Your chart will now display the hyetograph bars and the cumulative mass curve line on a secondary axis. To finalize, add a title for the secondary axis:

• Select the chart, click the plus icon (+) for Chart Elements, check Axis Titles.
• Click the secondary vertical axis title placeholder and set it to Cumulative Rainfall Depth (mm).

Final Thoughts

Creating a hyetograph in Excel is a straightforward process once you know the key steps. By using a column chart, setting the gap width to zero, and adding the right labels, you can transform simple rainfall data into a powerful and professional visualization for hydrological analysis. Layering on a cumulative mass curve with a secondary axis elevates your chart even further.

While Excel is fantastic for one-off analyses, we know that manually downloading CSVs and building the same charts week after week can be draining. We built Graphed to handle all that tedious work for you. You can connect your data sources directly and use plain English to ask for the charts and dashboards you need. It builds them instantly, keeps them updated in real-time, and frees you up to find insights instead of wrestling with formatting.