The amount of rain that falls in the Dutch summers has not yet decreased, but has become a lot more erratic. Summer rainstorms have almost doubled in our country. For example, it is possible that both drought and waterlogging occur more often.
This summer started exceptionally dry. Never before has it been as dry as this year on 1 June, at the start of the meteorological summer. But in the meantime we have had changeable weather for six weeks already, in which quite a few showers have passed. Does this fit into the picture of the summers of the future?
It certainly fits in with the current climate trend in the Netherlands, KNMI climate researcher Peter Siegmund tells NU.nl. Due to the influence of global warming, we have a greater risk of drought in the interior, but that is a direct consequence of the higher temperatures, which lead to more evaporation.
The average amount of rain in the Dutch summers has remained constant over the past few decades. Siegmund: "We calculate the average climate over a period of thirty years. Now we use the average from 1981 to 2010. In those thirty summers, an average of 224 millimeters of rain fell - exactly the same as in the summers between 1951 and 1980."
"The increase in downpours is because the air gets warmer and can therefore contain more water vapor." KNMI climate researcher Peter Siegmund
In the long term, drought and downpours more often
Any changes in precipitation in the past ten years have not yet been taken into account. At the beginning of next year, KNMI will come up with a new Dutch climate average, based on all measurements between 1991 and 2020.
In the long term, KNMI takes into account a scenario in which we get east winds more often in the summer and therefore there will be longer periods without rain. Together with the extra evaporation due to the higher temperatures and more sun, this means that the drought risk in the Netherlands is increasing.
But in addition to the possible shift in climate averages, there is another change going on: the rainfall is becoming more erratic, with a strong increase in downpours. In the summer, for example, the number of days during which an average of more than 20 millimeters of precipitation fell throughout the Netherlands increased by 77 percent between 1910 and 2017. Locally, more than 50 millimeters of precipitation is now recorded on nine summer days, while that occurred only five days a year forty years ago.
“Locally, more than 50 millimeters of precipitation is now recorded on nine summer days, while that was only five days a year forty years ago.”
Each degree of warming gives 14 percent higher rainfall intensity
That increase in downpours is because the air gets warmer and can therefore contain more water vapor, Siegmund says.
"As a result of the showers 7 percent more precipitation falls for every degree that it gets warmer. In addition, warmer air rises faster and therefore rains faster. This does not increase the amount of rain, but it does increase its intensity: it also goes up by about 7 percent for every degree it gets warmer. Overall, the precipitation intensity increases by about 14 percent with every degree it gets warmer. "
And the drought, is it over? No, certainly not. According to the KNMI's Drought Monitor, the precipitation deficit in the Netherlands is currently still greater than in the 5 percent driest summers. As soon as we do not receive rain for a few weeks in July or August, there is a good chance that drought problems for agriculture, nature and possibly inland shipping will reappear in a short time.
See also: Paradoxical: Our summers can get drier or wetter
See also: More drought in the Netherlands due to global warming, but no link with the North Pole
See also: Latest models: Climate change leads to an increase in droughts worldwide