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Global Ideas

Cities and the link to climate change

Germany is leading the way in urban climate research, and its universities approach the issue in different ways.

Foto: Model town in the wind tunnel (Foto: UHH/KlimaCampus/Huppertz)

Windkanal

Climate change has long since been recognized as a force to be reckoned with in emerging and developing nations, but how well are urban areas in industrial countries standing up to rising temperatures? It is generally assumed that cities, which consume two thirds of the world’s energy and 60 percent of water, and which generate 70 percent of greenhouse gas emissions, are climate demons - but that is not the whole picture. Cities, as Heinke Schlünzen, professor at the Meteorological Institute at Hamburg’s KlimaCampus explains, also bear the brunt of global warming. “Densely built cities warm up because heat from the sun and private homes and industry is stored between buildings.” And that, she adds, can make city living stressful and uncomfortable. “Many people don’t sleep well when it is more than 20 degrees at night.”

Hamburg as a test laboratory 



An observation station in front of a hedge at the climate campus in Hamburg (Foto: UHH/KlimaCampus)

Many Hamburg residents have observation stations like this in their gardens.

Schlünzen and her colleagues have turned the German city of Hamburg into a center for urban climate research. Observation stations have been set up across the city to measure air temperatures, humidity, precipitation, wind, ground water levels and temperatures. Stations transmit data to a computer at the KlimaCampus in order to find out to what extent ground water levels and ground characteristics affect evaporation, cooling, and the local city climate. The resulting urban models are exact enough to determine the impact individual buildings, parks and even groups of trees can have on the climate.

Researchers hope to be able to use their results to tackle the issue of rising night-time temperatures. For example, the Hamburg city government was considering building on top of the Outer Alster Lake, but researchers said a large area of stone would allow less water to evaporate, which would in turn remove the cooling effect. That was enough to convince the authorities to forget the idea.

Researchers supplemented the data with simulations from one of the biggest boundary layer wind tunnels in Europe. As project leader Bernd Leitl explains, the boundary layer reaches up to 100 to 200 meters above the ground, the range we use as living space. Miniature models of different cities such as Hamburg or Chicago show how the wind influences a given city’s climate and flow of pollutants.

On the whole, tall buildings are good for the aeration of a city because they channel the wind. If they are poorly positioned in relation to each other, they lead to the creation of fall winds, which stir the air up and consequently reduce temperatures. They also go hand-in-hand with strong gusts which make can make walking very unpleasant.

Skyline with cranes (Foto: ddp images/AP Photo/Elizabeth Dalziel)

In 50 years half of the city is regenerated.

Scientists therefore use the wind tunnel to test the effects of a new tower block on airflow. Schlünzen says her research focuses on making future generations as comfortable as possible. “We present the figures to inform politicians how best to design cities worth living in.”

And it is better to do it that way than to make changes after the fact, which is not only costly, but can lead to buildings having to be torn down because they block the path to a better urban climate.

Change of perspective: Focus on people not data

But Andreas Matzarakis, forestry and environmental science expert of the University of Freiburg, says the Hamburg measurements and statistics don’t go far enough. He believes what really counts is how people feel in a given climate. As a human meteorologist, he sees humans as a system in constant contact with their environment. “Temperatures and humidity are hard to influence and they have a far lower impact on the way people feel than we believe.”

Central Park in New York (Foto: ddp images/AP Photo/Susan Ragan)

Green spaces are naturally cool

A cool breeze in the face or a shady spot under a tree, however, can genuinely influence quality of life. In Freiburg, which is one of the warmest towns in Germany, scientists had a say in the design of a public square. Its lawns were earmarked to be replaced with stone terraces, but Matzarakis and his team warned against the idea on the basis that the stone would store heat and therefore make the square too hot to be comfortable for people to enjoy.

Local research on a global scale

Lydia Dümenil Gates, who is running a pilot project to create a network of research institutes exploring urban climate, says it doesn’t matter whether statistics or human beings are at the center of climate research, but rather collating information.

She hopes that cities will eventually share their experiences and solutions, but that requires greater support from universities and politicians. Platforms such as the Joint Programming Initiative (JPI), which aims to bundle climate information Europe-wide, can only go so far without co-operation and mutual support. And that in turn means the challenges of climate change will be hard to meet, both in rural areas of emerging and developing countries, and in mega cities of the future.

Author: Wiebke Feuersenger
/ tkw
Editor: Klaus Esterluss

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