Results of the "Urban climate in transition" funding measure

Cities are often a place of conflicting goals, for example between settlement pressure and climate adaptation. On the one hand, the proportion of built-up areas is increasing due to rising settlement pressure, while on the other, efforts are being made to adapt to the consequences of climate change with more open spaces and greenery. Reducing air pollution is also a challenge for many cities.

As part of the "Urban Climate in Transition" funding measure, researchers spent seven years (2015-2023) looking in detail at the impact of heat, storms and air pollutants on cities in Germany. The aim was to provide cities with a scientifically sound, practical set of tools for measuring urban climate pollution by global warming and air pollution. Adaptation measures to improve the temperatures in the summer in urban climate and keep the air clean can only be effective with a precisely recorded data basis. To this end, a new computer model for urban climate modeling was designed together with the future users, such as local authorities, who can now calculate pollution down to the level of buildings.

Methodological approach
First, the basic framework for the digital urban climate simulation model "PALM-4U" was developed. Important milestones included working out the practical requirements for such a model, carrying out several measurement campaigns at various locations in the city of Berlin and publishing an initial version of the model. Building on this, the project teams have further developed the urban climate model into an easily applicable product that meets the needs of local authorities and other users in research and practice.

In particular, a complete evaluation of the model and various further developments, a practice-oriented user interface and various tests for practical applications were carried out.

Results of the "Urban climate in transition" funding measure
The newly developed PALM-4U simulation model now enables cities to simulate (extreme) weather and climate down to the building level. This allows cities to calculate the extent to which districts are affected by heat and air pollutants and how climate adaptation measures work. The model makes it possible to check in advance how specific building projects will affect overheating effects and cold air flows. For example, different planning variants for buildings can be simulated. In this way, concrete recommendations for optimizing climate adaptation can already be made at the urban planning stage, for example for the positioning of buildings, the sealing of surfaces and greening through tree planting. In this way, the effective impact of climate adaptation measures can be determined quantitatively - this is a significant step forward compared to the previously prevailing, merely qualitative basic assumptions in urban planning procedures.

The PALM-4U urban climate model can be used accordingly to support municipal offices and authorities in the areas of environment, climate protection, open space planning, urban development, urban planning, housing, traffic planning and health. Other players in urban planning, such as architects and associations, also use the model. Last but not least, it is used and further developed in international urban climate research in order to increase the effectiveness of climate adaptation measures.

How does the "PALM-4U" urban climate model work?
Technically, the PALM-4U simulation model takes into account all urban surfaces such as trees, streets and water surfaces and calculates, for example, wind currents, temperature distributions as well as air chemistry and particulate matter distributions. The "PALM-4U" model provides so-called digital multi-agent systems for the simulations, so that the effects of heat and particulate matter can be calculated individually for people moving around the urban area.

The urban climate model can also be coupled with various regional climate models. The model is available in two variants, firstly for extremely high-resolution simulations (Large Eddy Simulations; LES) and secondly for resource-saving simulations (Reynolds-Averaged Navier Stokes; RANS). Overall, the model is suitable for many different applications - this has been shown by scientific evaluations with large measurement campaigns that were carried out with innovative measuring devices as part of the funding measure.

A web-based user interface has been specially developed for users from the field, such as local authorities. The interface provides graphical access to the model, which can be used to interactively simulate many applications. In just a few steps, for example, the different impacts on local heat effects of different urban planning concepts, such as the shape or position of buildings, can be compared.

Practical transfer to local authorities
PALM-4U has been successfully transferred into practice: Companies, service providers and local authorities in many municipalities in Germany are already using the urban climate software to plan effective climate adaptation measures. These include the cities of Berlin and Dresden, for example. Furthermore, ENERCON GmbH, the largest German manufacturer of wind turbines, uses the simulation model in the site assessment for wind turbines. PALM-4U is also a German contribution to assuming global responsibility for adapting to climate change: The urban climate software is already being used in partner countries, such as the USA.

Users in municipalities and in other practical areas are supported by the Climate Service Center GERICS and the Fraunhofer Institute for Building Physics IBP with the PALM-4U HUB platform (the graphical user interface) and training courses, as well as the German Weather Service (DWD), the agency GEO-NET Consulting and other providers of services related to the platform.
The PALM-4U computer model can be downloaded free of charge from the University of Hannover.