Extreme flooding in Zuid-Holland would cause €2 billion in damage, study shows

The Netherlands should expect 2 billion euros in damage if the densely populated Zuid-Holland province gets hit by extreme rainfall as severe as what happened in Limburg in the summer of 2021. The amount of money is a “conservative estimate,” said Deltares, who participated in the study with different governing bodies.

The occurrence of extreme showers is unavoidable. It is possible to prepare for them, the institute emphasized. That said, urban areas would be less affected than rural areas. It is also a stroke of luck that the chance of fatalities would be "very small" according to the stress test model organized by the research institute.

Deltares carried out the case study together with the province, the water boards, security region offices, Rijkswaterstaat and the municipalities of Rotterdam and Dordrecht. Together, they calculated models, held working sessions to analyze different scenarios, and had experts look at various aspects of flooding.

In the scenarios that have been calculated, 150 or 200 millimeters of rainfall hit the entire area over two days. Subsequently, it was calculated and reasoned what such extreme showers would do to the water level, the quays, the electricity network and the roads.

Those consequences are mainly material, the authors of the study estimated. In many places, a layer of water would be on the fields and streets for several days, or even longer than a week. This applies to 40 percent of agricultural land, but far less in urban areas, where the quays are higher and more pumping stations are present. Moreover, the cities are mainly built on "relatively favorable locations" and not in the wettest polders.

The electricity would continue to function in most places, but the power would go out in a few places, according to the stress test. A minority of transformer houses are low-lying and would flood, causing some of the problems.

Low-lying stretches of road would certainly be flooded as a result of this type of rainfall. This in turn has consequences for the accessibility of, for example, hospitals and fire stations. "To prevent the consequences of large-scale precipitation systems from becoming disastrous, major efforts will be required from water boards and safety regions," said Deltares.

There were also no fatalities in Limburg during the flooding of 2021, though the same could not be said for Germany and Belgium where there were victims who died as a result of the rain. The extreme rainfall in a large area in Limburg caused hundreds of millions of euros in damage. Valkenburg was hit particularly hard because the Geul River overflowed. The river flows right through the town.