Nearly 12,000 homes in The Hague face surface water levels of at least 15 centimetres against their facades during a once-in-a-century rainstorm.
In 5,305 of those cases, the water would reach 30 centimetres high, according to data from water consultancy Nelen & Schuurmans published in the Climate Impact Atlas.
The calculations are based on an extreme storm delivering 70 millimetres of rain within a single hour, which is slightly less than the city receives across the entire month of September.
In the latest climate scenarios from the KNMI meteorological institute, a downpour of that intensity occurs roughly once every 100 years.
The study models the risks by looking at lower-lying ground, local drainage capacity through sewers and ditches, and prevailing groundwater levels. The 11,907 vulnerable homes make up 13% of all residential properties in the municipality, though whether damage occurs depends on property safeguards.
Unequal geographic impact
Vulnerable properties are unevenly distributed across the city. In the Huygenspark area, an estimated 469 homes would see at least 15 centimetres of water at their doors during extreme downpours, accounting for 56% of all properties in the neighbourhood.
Water problems can have a greater impact in poorer areas, neighbourhoods with many frail older residents, or districts with high shares of rental housing where tenants depend on landlords for maintenance.
Huygenspark ranks near the top of the municipality for poverty, health vulnerabilities among residents aged 65 and older, and rental percentages.
Property damage from rainfall is already a regular expense for residents. Data from the Dutch Association of Insurers shows Hague residents have claimed nearly €34 million in precipitation damage since 2007, with roughly €13 million of that total filed over the past five years.
Measures for heavy downpours
Because extreme storms remain rare, residents rarely take preventative measures in advance. Matthijs Kok, an emeritus professor of flood risk at TU Delft, notes that people seldom prepare properly for rare events, comparing it to how few homeowners install ceiling fire sprinklers.
If water threatens a home, emergency steps include deploying sandbags, fitting barriers across doorways, and blocking toilet bowls with a football or a weighed-down towel to stop backflow.
Removing garden tiles in favour of permeable paving or greenery also helps absorb runoff, along with using rain barrels that are emptied ahead of approaching storms.
