Urban Climate

Adaption to the Climate in Freiburg

Yesterday, Red Baron was on a field trip with climate researchers in Freiburg. The topic of the excursion open to the public was studies of the city climate with indications of possible adaptations. The tour started at the Freiburg Center for Medical-Meteorological Research.

 

The five gentlemen I first met there around 9 AM were not participants of the excursion, but as it turned out later, scientists who informed us about their work.

 

The institute has numerous measuring instruments to collect climate-relevant data, but because of the location between buildings, e.g., a wind measurement is only relevant locally. Therefore, another free-standing complete measuring station is located near the Freiburg airport.

On our tour of Freiburg, we first visited a particular measuring station investigating the influence of trees on the climate.

Urban trees suffer especially from soil sealing. That's why some of those in town are already artificially watered. 

Until now, I had always assumed that deep-rooted trees tolerate climate change and the decreasing precipitation better than shallow-rooted trees. However, due to the previous dry summers, the soil has dried out to a depth of 1.50 m, so shallow-rooted trees have an advantage with the bit of rain that only wettens the surface.

There is no ideal urban tree. Sycamore trees would still be the most suitable, but they emit the climate-damaging gas isopropanol. As a compromise, in the future, one has to select tree varieties that can best tolerate heat and water stress.

The next stop on our excursion was a measuring station of the University of Freiburg mounted high on a lamppost.

Here is a measuring station downtown on a narrow street ...

... and on the Square of the Old Synagogue with a view of the municipal theater.

There are 42 meteorological stations spread throughout the city.

The scientists accompanying the tour presented their research results in a lecture hall of the university.

There are many fields of action for climate adaptation in Freiburg. I shall only mention the measures envisaged against excessive heat.

Click on the pictures to enlarge.

Measures to improve the urban structure against heat start with an optimized layout of the residential buildings, providing for green courtyards, larger open spaces, and installing reflective surfaces.

Water serves several roles in climate adaptation. Freiburg's Bächle have more of a psychological influence; more extensive areas of water generate a cooling effect, and rainwater is collected in pits and then infiltrates into the ground. With excessive heat, it's also important to provide sufficient drinking fountains distributed throughout the city.

The basis for the studies on the urban climate is the data from the measuring stations.

In Freiburg, the number of tropical nights* has increased from a few per year to more than 20 in recent years. Here is the temperature distribution of a tropical night in Freiburg.

*During the night, the temperature does not fall below 20 °C between 6 PM and 6 AM

 

Supported by the measurement system, a well-being index for Freiburg was simulated. This index considers not only the air temperature but also parameters such as humidity and wind movements. Four areas of the city are highlighted for an air temperature of 32 °C. 

The city center, the industrial area in the north, a tree-lined villa district in Herdern, and the Rieselfeld quarter with its young stock of trees. As expected, the unshaded industrial center is the most hostile environment, the Platz der Alten Synagoge in the city is a hot spot, and a dense tree population has a marked cooling effect. Note that the other "red-colored" district on the overall map is Freiburg‘s industrial area in the south.

Red Baron's conclusion: take care of existing city trees and plant new ones if possible.

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