The Netherlands is very dry, for the fourth summer in five years. Climate models expect such droughts for the future of the Netherlands, but not yet. Climate scientists are puzzled: is this a coincidence or is climate change happening even faster than thought?
The warmer our summers get, the more water evaporates – and the faster the soil dries out if the rain doesn’t stop for a while. Due to the direct link between temperature and evaporation, climate change is (already) making drought worse, according to the KNMI.
But climate change could further increase the risk of summer droughts. This is due to the summer rain. It has two faces: downpours are increasing – and periods without rain are getting longer.
Stubborn high pressure area
At least that’s what climate models expect for our summers in the future – say from 2050, when the global temperature is even warmer than it is today. Due to a combination of warming around the North Pole and the weakening of the warm Gulf Stream, persistent high pressure areas are expected over the British Isles and the North Sea in summer. These high pressure areas can lead to a ‘blockage’ of the European weather. That weather consists of much of the same.
If that high pressure area is above the Netherlands, we have (long-term) sunny and dry weather. The average summer precipitation will therefore decrease, in an (even) warmer future – thus further increasing the drought risk.
“If it becomes one degree warmer, for example, the precipitation per summer month will decrease by an average of 5 millimeters according to climate models,” says climate researcher Karin van der Wiel of the KNMI. “In addition, we then receive an extra 3 to 10 millimeters of evaporation per month. That together gives a doubling of the drought risk.”
Climate change increases the chance of a ‘persistent high pressure area’ over the British Isles. As a result, the Netherlands gets longer periods without rain in summer. But if a low-pressure area does slip through, it can become trapped. All precipitation falls in one place. Last summer, this pattern led to the flooding in Limburg.
Climate change increases the chance of a ‘persistent high pressure area’ over the British Isles. As a result, the Netherlands gets longer periods without rain in summer. But if a low-pressure area does slip through, it can become trapped. All precipitation falls in one place. Last summer, this pattern led to the flooding in Limburg. Photo: Bart-Jan Dekker, NU.nl
All summers since 2018 have been extreme
If air pressure areas are ‘blocked’ more often, the reverse situation can also occur, in which we are under a trapped low pressure area for a long time. That means a lot of rain in one place.
We saw that in the summer of 2021. A small area of low pressure completely rained out over the Ardennes and the Eifel. Just three days of rain, and the Meuse reached the highest discharge ever recorded.
We are a year later and now the Rhine has the lowest discharge ever. We are therefore under the influence of high air pressure for a long time. Just like in 2018, 2019 and 2020 – when it was not only very dry, but also exceptionally hot, with a new national heat record, above 40 degrees.
Climate models underestimate this increase in summer heat, said KNMI expert Geert Jan van Oldenborgh, who died last year. For example, the warmest day of the year in the Netherlands is already 4 degrees warmer than a century ago. That is more than twice as fast as models expected.
This climate puzzle has not yet been completed
Does this underestimation also apply to drought and extreme rainfall? The expert in the field of ‘stubborn weather’ is climate researcher Dim Coumou, who is affiliated with the Free University, among others. He calls the pattern in the last summers striking, and says he is currently investigating whether there is indeed an underestimation by models. But he cannot anticipate the results yet.
British jet stream expert Tim Woollings of Oxford University also says he should stick to suspicions. “We know that climate models often underestimate variability on short time scales. So it’s possible they’re missing something there. But it could also be the global warming trend.”
Loosely translated: the past five summers have been very extreme. But whether that was a coincidence, or whether climate change is actually happening faster than expected – even the best experts have yet to answer the question.