How Climate Change Affects Transportation Systems - Part 2: Flooding

This article is part of a series on the effects that climate change has on transportation systems.

Floods have always been enemies of transportation systems. When a street or railroad is flooded, then nothing can pass. A receding flood often leaves the tracks damaged. Most kinds of floods come slowly, preceded by days of heavy rain or snow melt. We can prepare for them, erect barricades and hope to avoid the worst that way. But with climate change, we get more and more so-called flash floods. In a flash flood, huge amounts of water pour down in a single place. This is often caused by storm cells that do not move. The amounts of water coming down are too much for drainage systems in cities, but also too much for small rivers to handle. Then streets can get flooded really quickly, with little time for man and machine to prepare. Let’s look at two recent examples from Germany.

Nuremberg: A Tramway Goes Under

On August 17th 2023, a tramway train in Nuremberg went out of service for 6 months. Not due to an accident with a car, neither due to scheduled repairs. Instead, it was under the water, in the true sense of the word.

What happened? On that day, a thunderstorm hit Nuremberg and unloaded up to 45 l per square meter.¹ This was too much to be taken away by the city’s drainage system. It flooded streets and cellars, and several underpasses. The water came so suddenly that several cars were trapped in the flooded underpass and passengers had to be rescued.

Also a tramway was stuck in an underpass that was suddenly full of water. The driver even wanted to drive the train back to save it from being damaged by the rising water. But then the power supply had to be cut so that firefighters could reach the cars that were already stuck in the water. The water rose and flooded the immobile tram.

Luckily, nobody died during this incident. But the affected tramway train was afterwards full of water. It was pulled back to the workshop, where the maintenance personnel weighed it. The tram had gained 300 kg — all water, and dirty water! It needed a complete revamp. It took 6 months to replace the electronics and the upholstery, clean the ventilation system and find all the pockets of water that were hidden in the tram’s understructure.²

The Ahrtal Flood

An even more massive flood happened two years before in the Ahr Valley. A flash flood caused the death of more than 140 people and even more were injured.³ Many people lost their homes. Reconstruction took several years.

The flood also caused massive damage to infrastructure. Seven railway bridges had been destroyed, as well as 20 km of tracks. Several trains were on the tracks at that time and got marooned. Some of them were also flooded, like in Nuremberg.⁴ Street, water and electricity infrastructure were also strongly affected by the flood.

In the aftermath of the tragedy, the railway infrastructure was rebuild to be more resilient against future floods.

The real tragedy is that all of this damage likely could have been prevented. The Ahr Valley had seen extreme floods more than 100 years ago.⁵ Even at that time, local authorities knew the countermeasure. They planned to build more retention basins. Alas, these plans were eventually abandoned. Instead, more and more ground was sealed, leading to even less ways for the water to go. This set the stage for the next disaster, several generations later.

Outlook

These are just two examples of floods that caused extreme effects on transportation infrastructure. More examples exist, and more will occur unless we prepare our infrastructure.

Climate change makes extreme floods more likely. We must take stronger measures against their effects. In many places, such as the Ahr Valley, countermeasures are known but need implementation: build more retention basins, unseal land so floods can infiltrate and recede faster, and design bridges to reduce the risk that flotsam becomes lodged in bridge piers.

This is especially important because extreme weather can quickly cascade into failures of other services. Floods can cause power outages, and rescue personnel may be unable to reach emergency sites because roads are submerged or bridges are destroyed.

Going forward, all infrastructure needs to be designed with resilience in mind. Only in this way can we prevent excessive loss of life and keep towns, cities, and societies functioning.

In the next article of this series, we will look into the opposite of floods: Droughts.

Footnotes