The Netherlands will “probably” have the technical means to cope with a rise in sea level of up to three metres but it will take a thorough and costly overhaul of the country’s dykes, according to a report commissioned by the infrastructure ministry and the Delta commission in charge of coastal defense.

In order to tackle a three-metre rise, some dykes will need to be widened by around 90 metres, which will not always be possible in the existing urban situation, Jos van Alphen, strategic advisor to the Delta commission, told broadcaster NOS.

A rise of one metre will make it necessary to strengthen 2,100 kilometres of coastal defence infrastructure, the report said. “We will need much more sand,” Van Alphen said, “and that means a tighter grip on the use of space in the North Sea.”

The report is based on the Dutch weather bureau KNMI’s latest climate scenarios which show that sea level rise cannot be predicted with any certainty, as much depends on the amount global greenhouse gas emissions and the rate of ice mass loss in the Antarctic.

In the worst case scenario, the North Sea will rise by one to two metres in this century and by three to five metres by around 2150, the KNMI said earlier this year.

However, strengthening the country’s coastal defense system will also have negative consequences. A solid coastal defense will cause other water-related problems as it will become increasingly difficult to discharge river water into the sea, necessitating giant pumps, Maarten Kleinhans, Utrecht University professor of physical geography, told NOS.

The land below the dykes will be relatively deeper, making it harder to get rid of rain water. Pumping will also extract more salt water which is detrimental to agriculture. A lack of fresh water in rivers because of a shortage of rainfall is also a threat, Kleinhans said.

“The problem is only being looked at from a technical point of view,” Kleinhans said. “Building a solid wall of coastal defences is not necessarily the best option.

“Many other questions need answering too, such as where do we want to live, how will we work, guarantees about wildlife and how cost-effective is it all going to be? This needs to be looked at from many more different angles and disciplines.”

The problem for the planners is that time is of the essence, Van Alphen said. “Important investments of hundreds of billions of euros in housing and infrastructure are being made for the next hundred years. “That means we have to figure out now if we are doing that in the right place,” he said.