While summers in Germany are increasingly characterized by periods of heat and drought, winters tend to be wetter.
In addition, extreme weather events with heavy rain are increasing, which, according to the GDV, have caused damage of more than 12 million euros to residential buildings alone in this country in the last 20 years1 . Gregor Grassl, associate partner and expert in sustainable urban development at Drees & Sommer SE, explains in an interview how cities and municipalities are already adapting to current and impending climatic changes in order to avoid damage and maintain livable cities.
1 Heavy rain balance from 2002 to 2021: 12.6 billion euros in damage nationwide (gdv.de)
Finanz.net: Mr. Grassl, in the recent past the construction and real estate industry has made great efforts to promote more climate protection, from circular construction to increased material recycling to plus-energy buildings. Were these efforts all in vain when we now talk about climate adaptation?
Gregor Grassl: They certainly weren’t and aren’t! Efforts to ensure consistent climate protection and the highest possible CO2 reduction remain absolutely necessary in the industry. After all, the construction and real estate sector causes around 40 percent of global greenhouse gas emissions and consumes more than half of global resources. However, extreme weather events make it clear that the effects of climate change have already arrived in Germany. It is therefore necessary that we address the consequences for our built environment now and make our cities climate-fit.
What are the differences between measures for climate protection and climate adaptation and how are they compatible with each other?
Often they even go hand in hand. However, it can happen that they are associated with conflicting interests during implementation and therefore collide. An example of this is the discussion about either greening roofs or equipping them with photovoltaic systems. The former is a measure of climate adaptation, the latter of climate protection. Numerous studies suggest that both can be combined and that synergies can even arise. Photovoltaic modules on green roofs achieve a higher yield because they work better by cooling the green roof. Another example are solar settlements, whose strict southerly orientation can in individual cases lead to them disrupting the important ventilation of the city. It is therefore important to always examine measures from different perspectives in order to identify and optimally exploit potential for both climate protection and climate adaptation.
In which areas is there the greatest need for action in cities to adapt to climate change?
When it comes to climatic changes, the problem in our cities is usually not the dense buildings, but rather the high level of sealing with heat-storing materials. These include, for example, concrete, asphalt or glass. This means that it can be up to 10 degrees warmer in the city than in the surrounding area. In this case we speak of so-called urban heat or heat islands. Due to the heat island effect, hot days in cities of over 30 degrees are more often accompanied by tropical nights in which the temperature does not drop below 20 degrees. The prolonged heat stress means constant stress for the body and can become a serious health risk, especially for older people, people with cardiovascular diseases and small children. So our goal should be a zero heat island effect. Other important issues include water supply and flood and flood protection.
What are concrete measures that cities can take to arm themselves against increasing heat, drought or heavy rain?
To improve water availability, rainwater can be collected using tree trenches, deep beds and cisterns and retrieved when necessary. At the same time, green spaces mitigate weather extremes by absorbing water like a sponge. The core of adapting to the natural force of rainwater is the so-called blue-green infrastructure – it combines green spaces, water management and the strategic use of modern technology. An example of blue-green infrastructure are parks that serve as recreational areas and transform into a lake or canal during cloudbursts, thus naturally absorbing large amounts of water. Flood protection, heat protection, air pollution control and biodiversity can be achieved through a single measure – at the same time, attractive living spaces are created for city residents.
To combat heat stress in the city, shading buildings and open spaces with trees or awnings is one of the best, simplest and most cost-effective means with the greatest immediate effect. Green areas, roofs and facades also provide evaporative cooling. Unsealing as well as bright and reflective surface materials with low heat storage capacity help to prevent inner cities from heating up so much. There are already the first applications of light-colored road surfaces.
Buildings will still heat up inside if temperatures remain high for long periods of time. Will we need air conditioning in all buildings in the future?
Air conditioning systems such as split devices cool the interior, but at the same time heat the outside space even further due to the waste heat. They are also huge energy guzzlers. At building level, so-called low-tech systems at low temperature levels are therefore increasingly being used as an alternative. A lot of storage mass is built into the building, which cools the interior at night using the cooler outside air. Underfloor heating can become a cooling floor in summer and ceilings can serve as cooling surfaces as part of component activation. Geothermal energy can also be used not only for heating, but also for cooling. There are therefore various climate-friendly solutions for interior cooling.
Overall, there is a wide range of CO2-neutral solutions available for adapting cities to the climate. Similar to how we as energy consultants go through buildings and look for optimization approaches to save energy for our wallets and the environment, cities should now also do the same for climate adaptation. Cities and municipalities will present possible solutions as part of the nationwide Climate Adaptation Week from September 18th to 22nd, 2023, which the Climate Adaptation Center (ZKA) is organizing together with the Federal Environment Ministry and which Drees & Sommer supports as a partner.
1 Heavy rain balance from 2002 to 2021: 12.6 billion euros in damage nationwide (gdv.de)
About Gregor Grassl:
Gregor Grassl is an associate partner at the construction and real estate consulting firm Drees & Sommer SE, headquartered in Stuttgart. He studied architecture in Munich and then urban planning in Stuttgart. In 2007 he started at Drees & Sommer. The focus of his work is in the area of sustainable urban and neighborhood development – and in particular on climate protection and climate adaptation concepts. In 2013, Gregor Grassl was appointed to the “National Platform for the City of the Future” by the Federal Government’s Future Initiative. He is also co-author of the specialist book “Sustainable Urban Planning” and teaches prospective DGNB auditors and consultants at the DGNB Academy.