Extreme gusts of wind of more than 40 km per hour are common on Hamburg’s footpaths. Measurements undertaken by Professor Felix Ament and Dr. Sarah Wiesner from the Center for Earth System Research and Sustainability (CEN) at Universität Hamburg demonstrate this. Their current measuring campaign has yielded data for a calculation model capable of determining wind conditions at specific locations with a hitherto unknown level of detail.
Felix Ament and Sarah Wiesner measure wind conditions around the Hafencity University building in a prototype experiment. Their results show that gusts of wind are more frequent and stronger in the city center than in suburban areas.
The area around the underground exit HafenCity Universität is particularly badly affected: when south-westerly winds prevail, this location experiences gusts of wind that are 4 times as fast as the normal wind speed. Under such conditions, pedestrians with umbrellas are subject to extreme force, as the wind pressure increases with the square root of wind velocity. "To keep hold of your umbrella during a gust of wind in the city, you need 5 times the strength," the meteorologist Sarah Wiesner explains, "and if the gusts are coming from the south-west, you need 16 times the strength. A wind as strong as that can upend rubbish bins or push over signs."
Six measuring stations roughly 20 meters apart have been erected in front of the building. They show clearly how variably city winds blow: although the masts are close to one another, wind velocity and wind direction measurements differ enormously. "Knowing what the wind is doing is the prerequisite for further parameters," says Felix Ament. "The wind determines how pollutants are distributed, the levels of particulate matter in the air, and where heat is retained in summer--all of these factors are driven by the wind."
Using this data, the researchers are developing a calculation model for urban planning for use, for example, by municipal authorities. "We will then be able to say which corner is suitable for a café or what wind effect an 8-storey new build will have on pedestrians," says Sarah Wiesner. Measures to combat windy corners--for example trees or protective hedges--can then be tested first for their actual effect using a model.
In the case of the extreme gusts at the underground exit, it is possible that the University building is the culprit. New measurements suggest that the wind may have been reduced if the planers had forgone the north-eastern tip of the building. Once in use, the calculation model for urban planning will be able to provide greater detail.
The measurement campaign is part of the BMBF project "Urban Climate Under Change." As part of the project, scientists in Berlin and Stuttgart are also measuring temperature and particulate matter.