Higher dykes won't save NL from climate change consequences

With the world seeming to be heading towards global warming of 3 degrees Celsius, the Netherlands will be facing some very major consequences, Maarten Kleinhans, professor of physical geography at Utrecht University, said to newspaper NU.nl.

Last week, KNMI director Gerard van der Steenhoven told NOS that limiting global warming to 1.5 degrees Celsius may already be impossible. A recent study showed that global warming resulting from emissions from the past may have been greatly underestimated. Areas that warm more slowly, such as the Southern Ocean, will eventually catch up and can amplify global warming. A warming of 2.3 degrees could already be inevitable, and that doesn't even account for future greenhouse gas emissions.

The world may be heading to 3 degrees of warming, Van der Steenhoven said. "That leads to a dramatic situation. Everyone will have to realize that we really have to get started." He called on the next cabinet to take real steps to reduce emissions and further combat global warming.

Kleinhans agrees that 3 degrees of global warming will have dire consequences. "An inescapable consequence of 3 degrees for the second generation after us is the unstoppable sea level rise. And with the sea, the rivers rise over the entire width of the Netherlands. In the river area we now protect cities during extremely high water by discharging water into sparsely populated polders, but with backwater by seawater that makes no sense anymore."

The Netherlands is something of a delta with the estuary of the Rhine, Maas, Scheldt and Ems in the North Sea. Natural processes can keep such a delta in balance and even absorb some sea level rise, but those natural processes haven't been allowed to occur for years, Kleinhans said. The problem is the dikes. They prevent rivers overflowing and entering the sea at every high tide. But those small floods is what made the Netherlands by depositing clay, and that hasn't happened for centuries. 

Peatlands are also de-watered. That combined with the dykes means that the soil continues to settle and subside, and half of the Netherlands becoming deeper and deeper, behind higher and higher dykes. That means that more and more drainage is needed to keep the polders dry. But the drainage results in salt seawater being sucked in under the dykes, which has major consequences for agriculture, Kleinhans said. 

According to Kleinhans, the problem of climate change needs to first be tackled at the source - eliminating greenhouse gas emissions. In addition, the Netherlands should not look at higher dykes and deeper polders, but instead attempt to raise the land slightly where possible. "Along the Scheldt and Eems, this can be done with controlled flooding, in so called exchange polders. We have a water policy in the Netherlands, but should also pursue a 'sediment policy' - to stop the sinking of the Netherlands."