Blog 3: One meter of sea level rise: 2.6 million additional Dutch people living below sea level

When global sea levels rise with 1 meter, the number of Dutch people living below sea level will increase from 3.93 million to 6.57 million, research from Delft University of Technology scientists Olivier Hoes and Rolf Hut show.

Currently, at the United Nations Climate Conference in Paris, the nations of the world negotiate a treaty on the reduction of greenhouse gases. Increased greenhouse gases lead to global warming, melting of the (polar) ice sheets and sea level rise: a threat to the population of the Netherlands where currently 3.93 million people live below mean sea level. 
However, a mean sea level rise of a meter does not mean that 2.6 million Dutch people have to move houses. The Netherlands is protected from the sea by a complex system of levees, dunes, dikes and man-made barriers. A rise in mean sea levels does mean that some of these defences will need to be strengthened.

Olivier Hoes calculated the number of people living below mean sea level by coupling multiple open access databases. First, the building register from the Cadaster was coupled to a high resolution elevation map (AHN2) to determine the height of each building above (or below) sea level. Using population statistics on a neighbourhood level from Statistics Netherlands (CBS), the amount of people living in each house was added to the house-information. Thus Olivier could determine how many people live at what elevation. This is the first time that such an analyses has been done using information on individual houses. By looking at individual houses, the exact height above sea level could be determined more accurately compared to when aggregated input sources would have been used. 

Whilst doing these analyses, Olivier Hoes and Rolf Hut had fruitful discussions with Niek van Leeuwen from Statistics Netherlands and Jaap Schellekens and Gennadii Donchyts from Deltares. 

For mean sea level, we use the Amsterdam Ordnance Datum. This datum is widely used as mean sea level, but is not exactly equal to the mean sea level in the North Sea. See en.wikipedia.org/wiki/Amsterdam_Ordnance_Datum for more information.