New Study Reveals Europe’s Most Underestimated Flood Risks

Every workday, more than 300,000 people are inside Hamburg’s flood zones, according to a September 2026 report on flooding risks across Europe.

This new study by crisis management software provider Intersec reveals the top 10 European cities where daytime flood danger could be underestimated.

The research examined over 1,000 European regions to find where flood emergency plans are built around the wrong population. The report measured how many people are physically present inside river flood zones during the day versus at night, using modelled population data for each region.

It then crossed those figures against Copernicus flood maps showing where water would reach in a severe river flood. Regions were ranked by how many more people are in their flood zones during working hours than overnight.

5 European regions where daytime flood risk is underestimated the most

1. Hamburg, Germany

• Additional people in flood zone by day vs. night: 138K
• Nighttime flood population:2K
• Daytime flood population:1K
• Daytime-to-nighttime flood population ratio:66

The flooding risks in Hamburg increase significantly during daytime. Around 190,000 people live inside the city’s flood zones, but since it’s a major port and commercial hub, it draws in large numbers of workers from surrounding areas every morning.

By the time the workday begins, that number climbs to 315,000 people inside those same zones. That daily influx of workers is a factor that flood emergency planning needs to account for.

2. Hauts-de-Seine, France

Hauts-de-Seine, the dense business district west of Paris, ranks second with nearly 133,000 extra people in flood zones during working hours. The area is home to La Défense, France’s largest office district, which draws big flows of commuters every day.

At night, around 334,000 people are physically present in the flood zone, but by day, that number is usually up 22%. Overall, nearly half a million Parisians are inside its flood zones on a typical workday.

3. Rome, Italy

Rome is one of Europe’s most visited cities, which means its flood zones look very different during the day than at night. Around 175,000 Romans live inside those areas. But the city draws in enormous numbers of tourists and workers every single day on top of that, and by midday those same flood zones hold 289,000 people. That is 114,000 more than actually live there, and it raises the question of whether flood emergency plans always account for that daily reality.

4. Miasto Wrocław, Poland

Wrocław sits at the junction of several rivers, and much of the city is already in a flood zone before commuting even starts. Around 115,000 people live inside those areas, but every morning, workers who arrive at their offices push that number to 212,000, nearly double the overnight figure. That is one of the sharpest day-to-night swings anywhere in Europe, highlighting how important it is for emergency plans to consider the live daytime population.

5. Frankfurt am Main, Germany

Frankfurt is Germany’s financial capital and has more jobs than residents, meaning more people are in the city during working hours than actually live there. Around 139,000 residents live inside Frankfurt’s flood zones. But every morning, banking and finance workers commute in from surrounding areas, pushing that number to 227,000 by midday. Overall, that is 88K more people inside Frankfurt’s flood zones every workday than the residential population alone would suggest.

“Most flood emergency plans rely on census data, which only shows where people live. If a flood hits on a Tuesday, emergency teams are making life-or-death decisions based on headcount estimates that could be off by 50% or more, especially if an unannounced event brings thousands more into the zone. To fix this, authorities need live situational awareness using mobile network data to see real-time crowd movements. By pairing that live data with AI and river-level sensors, decision-makers can pinpoint immediate threats, route traffic effectively, and issue evacuation alerts at the exact right moment,” an emergency specialist from Intersec commented on the findings.

Top 10 European regions where daytime flood risk is underestimated the most