The effects of climate change are already noticeable in Dutch summers. For example, heat waves are more common and extreme amounts of rain fall more often. These six charts show how our summers have changed.
We start with the temperature. Since the pre-industrial era, the earth has already warmed by about 1.2 degrees. But that is an average over the entire globe and throughout the year. There are big differences by location and season.
For example, the average maximum temperature in Dutch summers has already risen by more than 2 degrees. While it was about 20 degrees on an average summer afternoon at the beginning of the twentieth century, it is now more than 22 degrees.
Warmer nights too
If we also include the nighttime temperature, the increase is even stronger. The average temperature over the entire summer day (from June to August) has risen in more than a century from 15.4 to almost 18 degrees.
Hottest days are getting hotter
That is the temperature average over the whole summer. But climate change also makes the heat extremes even more extreme. This can be clearly seen when we look at the temperature on the hottest day of the year.
In the twentieth century it still regularly happened that the mercury never rose above 30 degrees all year round. But now it is an average of 33 degrees on the hottest day of the year. It has not happened since 1993 that it remained colder than 30 degrees in De Bilt all year round.
European summers are getting warmer quickly
For every degree that the entire earth warms up, the hottest day in the Netherlands will be no less than 3.3 degrees warmer, the KNMI recently calculated. In the Netherlands, the hottest summer day is now 4 degrees warmer than a century ago.
This effect is much stronger in Europe than in other parts of the world, as can be seen on the map below.
Summers are not drier
You might think that our summers are also getting drier, but we see that effect in the Netherlands especially in the spring. The total amount of precipitation that falls in summer has remained fairly stable over the past century.
More heavy rain in summer
What has changed is how that rain falls from the sky. This often happens in large quantities at the same time. We will have to deal with the same weather types for a longer period of time, as a result of which both the heat from high-pressure areas and the rain from low-pressure areas remain above the Netherlands for longer.
The number of summer days with at least 10 millimeters of rain has risen sharply. The number of summer days with extreme rainfall of at least 20 millimeters is even on the way to a doubling compared to 1900.
Floods and heat
Last year we saw what consequences that could have in Limburg, Belgium and Germany. There was so much rain in two days that more than two hundred people died in flooding. The economic damage amounted to tens of billions of euros.
So much rain – just like temperatures approaching 40 degrees on Tuesday – is still an exception. But the warmer the globe gets, the more often these extremes will occur.