About a quarter of the Netherlands now sits below sea level, and the obvious explanation is that the sea rose. However, researchers who reconstructed the past thousand years of the Dutch coastal plain concluded the opposite — much of the land came down to meet the water
The Dutch blamed rising seas for their waterlogged land, but a thousand years of geological records tell a different story: the ground itself has been sinking.
By Science Blog Editorial Team
Excerpt:
Say “about quarter of the Netherlands is below sea level” out loud and the picture almost draws itself. The North Sea creeping higher over the centuries, the coastline pushed inland, the Dutch scrambling to hold back a rising tide with dikes and pumps.
It’s a tidy story, and it blames the water. The trouble is that when you look at what actually happened to the ground over the last thousand years, that story falls apart. It seems much of the land dropped relative to the water. That comes from a 2016 study in the Hydrogeology Journal by Gilles Erkens, Michiel van der Meulen and Hans Middelkoop, researchers tied to Deltares, the Geological Survey of the Netherlands, and Utrecht University. It’s a reconstruction built on modelling assumptions, not a direct measurement.
The intuitive story, and why it’s wrong
Most people cast the sea as the villain. And over very long stretches of geological time, rising seas really have reshaped this coastline. But for the specific thousand-year window the researchers studied, they treated global sea-level rise as close to zero. Local mean sea level still rose about 0.3 metres in their reconstruction because of background land subsidence. It’s a reconstruction of the pre-industrial past, not a claim about today’s seas, which are rising. If the sea itself changed relatively little over that millennium while large parts of the coastal plain ended up below it, something else had to give. What gave was the ground.
What the reconstruction actually found
The team created a reconstructed elevation model for around the year 1000 and compared it with a detailed modern elevation model. The gap between the two estimates how far the land fell. Peat loss pulled the surface down dramatically, leaving much of it below sea level.
The Netherlands didn’t lose that ground in a single dramatic flood. It lost it slowly, over centuries, to processes that began with cultivation. The study reports that 26% of the Netherlands lies below mean sea level, largely as a result of this.
Peat is basically waterlogged, partly decomposed plant matter. Starting between roughly AD 1000 and 1300, farmers drained the coastal peatlands to turn them into usable agricultural land. Drain peat and the material shrinks, oxidises and compacts. On top of that, people dug peat out and burned it as fuel. Both removed volume, and both pulled the land down.
The researchers split the loss between the two causes. “At least 66 % of the volume reduction is the result of drainage,” they write, “and 34 % was caused by the excavation and subsequent combustion of peat.”
The “at least” is their own hedge, and these are modelled estimates rather than surveyed fact. But the direction is clear: much of this land was lowered by how people used it, not by the North Sea rising over it.
The study estimates that “the peat volume loss was 19.8 km3, which lowered the Dutch coastal plain by 1.9 m on average, bringing most of it below sea level.” Almost twenty cubic kilometres of peat volume, gone. Nearly two metres of average lowering by the study’s summary measure.
How to read this going forward
What we keep coming back to is that this isn’t just a story about the medieval past. The process is still running. The authors put the reconstructed thousand-year average at about 1.9 millimetres a year for drainage-related subsidence, while citing present-day rates of 2 to 25 millimetres a year.
They describe a nasty loop: sinking farmland prompts further water-table lowering, which exposes more peat and causes further sinking.
Their forecast follows from that logic: subsidence will continue as long as water tables keep being lowered in the coastal peatlands. That “as long as” matters. It’s a condition, not a doom sentence, and the paper notes that the Netherlands has taken steps to reduce drainage depth in some peatlands.
The unsettling part is the math of the coming century. The sinking that put much of the coastal plain below the waterline unfolded during a millennium in which global sea-level rise was small. That’s no longer the case. Modern sea-level rise now stacks on top of land that is still subsiding in places, and the two pressures push the same way at once. A landscape that farming helped lower toward a relatively stable sea now has to reckon with a sea that is rising too.
