Climate researchers expect significantly more cloudbursts in Denmark

In the future, Denmark can expect more cloudbursts, more intense rainfall events, and a longer season for extreme precipitation. This is the assessment of the National Center for Climate Research (NCKF) at DMI.

While meteorologists work on forecasting the next cloudbursts, climate researchers are examining how developments will look in the longer term. According to Martin Olesen, a climate researcher at NCKF, all climate scenarios point in the same direction.

“There will be more cloudbursts in the future. How many more cloudbursts will depend on which emissions scenario we follow. We work with different scenarios for how many greenhouse gases will remain in the atmosphere through to the end of the century. What the scenarios have in common, however, is that they indicate that there will be more cloudbursts in the future.”

Today, Denmark experiences an average of around 20–25 days with cloudbursts per year. According to DMI’s calculations, this number could increase by between 25 and 70 percent by the end of the century.

Warmer air leads to more precipitation

The development is driven by global warming, which increases the atmosphere’s capacity to hold water vapour.

“A warmer atmosphere can contain more water vapour. A rule of thumb is that air that is one degree warmer can hold around seven percent more water vapour. This means there is more ‘fuel’ for heavy showers – and therefore a greater likelihood of cloudbursts,” says Martin Olesen.

In addition to more cloudbursts, researchers also expect the cloudburst season to become longer.

“We expect the cloudburst season to become longer as temperatures rise. In 2023, which was a warm year both in Denmark and globally, for example, we had the last cloudbursts in October. That is unusually late.”

At the same time, DMI assesses that the most extreme rainfall events will both become more intense and occur more frequently.

“Under the intermediate emissions scenario, a 50-year event will become a 20-year event, a 20-year event will become a 10-year event, and a 10-year event will become a 5-year event before the end of this century,” explains Martin Olesen.

Could create major problems in cities

According to the researchers, the development could have significant consequences for society, particularly in urban areas, where large volumes of rainwater can be difficult to manage.

“It can create major problems – especially in cities. Here, the large amounts of precipitation can cause flooding that may affect everything from infrastructure such as trains and metro systems to buildings, cultural heritage, and of course the buildings that are particularly exposed,” says Martin Olesen.

DMI also points out that the climate of the future may increase the risk of several extreme weather events occurring simultaneously. This could, for example, involve cloudbursts combined with storm surges or prolonged heavy rainfall, which could worsen flooding.

Work on climate adaptation in cities is already underway, but the effort is both extensive and costly.

“DMI provides warnings of extreme events, and this helps reduce the worst damage. But economically, we are facing major costs, both because cities cannot handle cloudbursts and storm surges in particular, and because we need to redesign cities so that the damage does not become unmanageable,” says Karsten Arnbjerg-Nielsen, a climate researcher at DMI.

According to DMI, extreme weather events cost Danish society between DKK 18 and 19 billion in the period from 2011 to 2023. The flooding in Copenhagen in the summer of 2011 alone cost more than DKK 6 billion.

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