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The main part of the annual precipitation

15 april 2024

All the rain added in a year covers the Netherlands with an average layer of water of 85 centimeters. Which days contribute most to this? Are those the many days with little precipitation, or the few days with a lot of precipitation, or something in between?

Counting days with a certain amount of precipitation

We take the measurement series from 13 precipitation stations spread across the Netherlands and count per station in the period 1991-2020 how many days per year occurred with a certain amount of precipitation. We do this in steps of 1 millimeter per day (image 1, black line). You see that days with the least precipitation, between 0.1 and 1 millimeter, are the most common. As the precipitation per day increases, the number of days with that precipitation decreases.

Contribution to annual precipitation

If you multiply the number of days by the amount of precipitation that day, you get the contribution to the annual precipitation. This is the blue line in image 1. For example, there are on average 12 days with 4 to 5 millimeters of precipitation, which together contribute around 54 millimeters to the annual precipitation. You see that days with around 5 millimeters of precipitation contribute most to the annual precipitation. Although there are (many) more days with less precipitation, together they contribute relatively little to the annual precipitation. The few days with (very) heavy precipitation also contribute relatively little.

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