Updated rain maps link extreme showers to hospital access risk
Three new maps show how deep water can get on Dutch streets during short, severe rainstorms. The maps cover downpours of 70 millimetres in one hour, 90 millimetres in one hour, and 150 millimetres in two hours. They have been published on the Climate Impact Atlas and are currently being integrated into the risk assessment tools and data access for pluvial flood risk on the Dutch Climate Risk Portal. Research used this type of flood data to show how vulnerable Dutch hospitals are to sudden, heavy rain, including cases where rainwater flooded emergency departments and blocked ambulances.
What do the new maps show?
The maps show, at a resolution of half a metre, exactly where water is likely to pool during a short but intense downpour. They replace older maps that were based on outdated elevation and rainfall data. The new versions use the latest climate scenarios from the Royal Netherlands Meteorological Institute (KNMI) and the most recent elevation data for the Netherlands. This makes it possible to see, street by street, how much water could gather around buildings, roads and critical infrastructure during a cloudburst.
Why does this matter for hospitals and emergency care?
Short, intense rainstorms can quickly overwhelm sewer systems in built-up areas. When researchers combined flood-depth data with the locations of hospitals, they found that seventeen out of seventy-seven Dutch hospitals offering emergency care risk flooding during such a storm. Seven of these hospitals could become unreachable for ambulances, forcing patients to travel much further to reach care. Cases already reported include flooding inside emergency departments and ambulances stuck in flooded streets, showing that this is not only a theoretical risk.
What this means for buildings and infrastructure more broadly
Heavy, short rainstorms affect far more than hospitals. Roads, tunnels, basements and fire stations can all become flooded or unreachable within a short time. Because the new maps show water depth at a detailed, local scale, they help identify which specific buildings or routes are most exposed. The maps can be used within the Framework for Climate Adaptive Buildings, allowing to assess climate risk at building level.
Who developed the maps?
The maps were developed through a collaboration between Deltares, Nelen and Schuurmans, the Dutch Green Building Council and Climate Adaptation Services.