Heavy rainfalls in the federal state of North Rhine-Westphalia, severe flooding in Tuscany, and even more devastating floods in Bali: heavy rain and flood events not only occur more frequently in Germany, but noticeably all over the world. From flooded basements to paralyzed infrastructure, billions in damage and even human casualties – the consequences are often disastrous. “For cities, towns and municipalities, comprehensive flood protection and climate-resilient urban planning are becoming crucial for the future,” says Gregor Grassl, Associate Partner at Drees & Sommer and an expert in the field of climate-friendly urban development. The Stuttgart-based company specializes in consulting on construction, real estate and infrastructure projects. The climate adaptation plans of the districts of Cochem-Zell and the cities of Limburg and Potsdam show how effective climate mitigation measures can be implemented in practice. Drees & Sommer’s teams of experts provide advice on this subject matter to the cities and municipalities.
Since July 2024, the German Climate Adaptation Act (Klimaanpassungsgesetz – KAnG) requires the German federal states to develop their own climate adaptation strategies. A representative survey entitled Municipal Survey on Climate Change Adaptation 2023, commissioned by the Federal Environment Agency (UBA), shows that a lot is already happening in this regard1. According to this study, over 40 percent of the more than 1,000 municipalities surveyed have already implemented climate adaptation measures, and almost as many are planning specific steps. Consequently, climate adaptation has become a key topic on the political agenda of cities, towns and villages. The study also showed that almost three quarters of the local administrative authorities would appreciate recommendations and more information on the topic of climate mitigation and adaptation measures.
While in some regions the rising temperatures are causing drought across entire expanses of land, other areas are almost drowning in heavy rain. At Drees & Sommer, Gregor Grassl is closely involved with the challenges posed by these extreme weather conditions. He points out: “The periods of heat and rain are becoming increasingly concentrated and can affect any region of Germany. Heavy rain is particularly treacherous because it falls spontaneously and sporadically, making it difficult to plan for.” Cities can nevertheless adapt and become more resilient if they have the right expertise.
How to Deal with Heavy Rain
1. Analyzing local risks
Heavy rain can devastate entire cities and make the risk of flooding difficult to calculate, even away from bodies of water. It is important to take preventive measures before these events in order to minimize the negative impact. “The condition of bodies of water and the ability of the sewer system to cope are key factors, as overloaded drainage lines are one of the most common causes of urban flooding," explains Drees & Sommer’s expert. This is why it is important to regularly review existing flood protection measures and test their effectiveness against extreme weather conditions. It is just as essential to ensure access to vital infrastructure such as rescue routes, fire stations, hospitals and emergency shelters at all times.
2. Promoting a blue-green infrastructure
The blue-green infrastructure is at the heart of the adaptation to heavy rainfall events. It combines green spaces, water management and modern technology. Parks, greenways and urban open spaces play a key role in this respect, since they act as natural retention areas that absorb excess water during heavy rainfall, and so mitigate the impact of the flooding effectively.
“In this context, we also talk about ‘sponge cities’, because the green areas act like a sponge and absorb the rainwater,” says Gregor Grassl . But the areas do much more than this: they provide protection from the heat, improve air quality, promote biodiversity, and create valuable recreational space in urban areas. So they not only contribute to climate adaptation, but also noticeably enhance the quality of life in our cities.
3. Avoiding soil sealing
Many cities have large amounts of materials that prevent rainwater from penetrating into the ground, such as asphalt, concrete and paving stones with no joints for moss or weeds to form in. So water flows unchecked into the drainage system, which quickly becomes overstretched during heavy rainfall. This results in backflows of water, and flooded streets and basements, causing enormous damage to buildings and infrastructure. “As a preventive measure, existing large impervious surfaces should be removed and replaced by water-permeable solutions,” explains Gregor Grassl. Grass pavers, porous covering materials or green access routes, for example, enable natural infiltration and help to absorb rainwater at decentralized locations where it falls. In addition, de-sealed surfaces can improve local microclimate conditions, protect cities from overheating, and they can also support the recharge of the groundwater.
4. Removing counterproductive dams
Traditional, rigid and counterproductive dams have long been regarded as an effective method of flood protection. In many cases, however, they have the opposite effect. By restricting the natural flow of water and diverting it to specific areas, they increase the flow velocity. This results in flooding elsewhere being exacerbated, or even caused in the first place.
This means that a sustainable approach to heavy rainfall events requires a paradigm shift: "Instead of quickly draining water away from urban areas, we need to slow it down in specific locations and buffer it. This means adapting cities and urban developments more closely to natural conditions such as terrain and original watercourses,” comments Drees & Sommer’s Associate Director. Retention areas, permeable soils and close-to-nature designs can be used to retain water locally for longer, allow it to seep away in a controlled way, or delay its onward flow.
5. Integration in urban development plans and land-use planning
In order to benefit from synergies and to reduce costs, heavy rain prevention measures must be integral part of the planning of conversion and construction projects at an early stage. This allows infiltration surfaces, stormwater retention basins and green corridors to be included in the planning and efficiently implemented from the outset. Gregor Grassl comments: “Integrated planning is not only important from a functional perspective but also for the design: retention areas can also be used as parks, playgrounds or recreational zones.”
Examples of current or successfully completed projects in which Drees & Sommer’s teams of experts are or have been engaged:
Climate adaptation in Cochem Zell – the district of Cochem-Zell, located in the federal state of Rhineland-Palatinate, is currently developing a comprehensive climate adaptation plan which is due to be completed by October 2026. It focuses on mitigation measures to reduce the increasing and visible impact climate chance is having in this region.
Climate adaptation solutions for Limburg – the city of Limburg actively promotes municipal heat planning, energy consulting for private house owners and a climate resilient design for public spaces as measures to counteract the impact of climate change.
Climate action plan for Potsdam’s Telegrafenberg – due to the heat and drought, up to 78 percent of the trees on Potsdam’s Telegrafenberg hill are considered damaged. With a comprehensive landscape plan, the long-established center of science will get ready for the future.
Climate adaptation in Düren und Dormagen – the district of Düren in the federal state of North Rhine-Westphalia and the city of Dormagen are developing individual climate adaptation concepts on the basis of impact analyses in order to be prepared for climate change.
Master plan for Hamburg’s university campus – the Helmut Schmidt University (HSU) plans a new, climate-neutral campus in Hamburg’s Jenfeld district. The master plan includes a comprehensive water management system, which is based on the principle of the sponge city
Source 1: Federal Environment Agency (UBA): Municipal Survey on Climate Change Adaptation 2023
