Number of the month: 40 kilometres per hour

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From one moment to the next, people walking around Hamburg's HafenCity district can find themselves exposed to some pretty hazardous weather conditions. When the wind really gets up, it can easily blow over rubbish bins and knock down display boards. Pedestrians sometimes have to use all their strength to stop their umbrellas from flying away. Gusts here can reach speeds of over 40 kilometres per hour, according to measurements taken by Professor Felix Ament and Dr Sarah Wiesner from the Center for Earth System Research and Sustainability (CEN) at Universität Hamburg. During their study, they found that gusts of wind occur in the city far more often than in suburban areas.

Wind speed measurements provide new data for urban planning

40 kilometres per hour

Buildings are one of the reasons why the wind reaches such high speeds. "It's like a stone in the water. It creates an obstacle to the flow and causes the water to swirl up behind it", explains meteorology professor Ament. To obtain their measurements, he and colleagues from the Technische Universität Dresden used not only several masts but also a balloon fitted with a wind sensor – which allowed them to record wind movements much more precisely than had previously been possible. Their results are accurate to within a few metres and to the nearest second. They even register very short gusts. Because measurement methods were not as precise in the past, Ament says, "extremes such as these would often go unrecorded". And yet this is exactly the kind of data that is needed, as such phenomena – like a powerful gust of wind, for instance – can have an impact on safety for people in the city.

The scientists used their findings to create a new computational model capable of accurately simulating wind patterns in cities. This is a useful tool for urban planners. "We can then determine where a good corner location for a street cafe would be, or what wind effect a new eight-storey building would have on pedestrians", explains Wiesner. Furthermore, the model allows urban planners to check the precise impact that steps taken to combat windy corners – such as trees or a protective hedge – will have. It may be that they will need to consider entirely new protective measures.

Model developed in a research network

The model was jointly developed by several research institutions in Germany within the framework of the "Urban Climate Under Change" project funded by the Federal Ministry of Education and Research (BMBF). An initial beta version was recently completed. In parallel, additional measurements are underway to further improve the computer simulation. The City of Hamburg is already planning to use the simulation on a trial basis in selected urban development projects. Temperature and particulate matter measurements in Berlin and Stuttgart are an additional part of the project, as are the data analyses in Hamburg.

Drone traffic: a further application

Future applications for the computational model are also conceivable, explains geoscientist Ament. It could be used for example in drone traffic. If courier drones are flying around the city in the future, the model could show which areas would be best to avoid due to extreme wind conditions. "We are making the invisible visible", says Ament.

Center for Earth System Research and Sustainability (CEN)

CEN is a central research centre at Universität Hamburg. Members include oceanographers, meteorologists, marine biologists, economists, social scientists and historians, all of whom are actively engaged in climate, environmental and earth system research. CEN therefore links the natural and social sciences.

www.cen.uni-hamburg.de