With climate change, conditions in cities are also changing. They are getting hotter and in some places they receive a lot or very little rain. The newly developed online tool “CityTree” now shows which trees can still thrive under these conditions and cool down their surroundings. It is intended to make it easier for municipalities to adapt their tree populations to the respective local conditions and to prepare themselves for further global warming.
Trees bind the greenhouse gas CO2 and are therefore an important factor in climate protection – on a global and local level. For cities, trees also act as a natural air conditioning system, because on hot days they reduce the heat stress for residents through their shade and evaporation as cool oases. In the wake of global warming, they help to improve the quality of life in urban areas and prevent heat-related deaths and other health consequences. But not all trees thrive everywhere and do not always provide the same cooling capacity.
Online tool facilitates data comparison
A research team led by Thomas Rötzer from the Technical University of Munich has now investigated the advantages that selected tree species bring to the urban climate and the conditions under which they grow well. To do this, the forestry scientists measured more than 5,600 urban trees across Germany, took samples and analyzed the surrounding area. The focus was on the twelve most common tree species – including maple, beech, chestnut, linden, plane tree and robinia – which together currently make up 60 percent of the tree population in German cities.
The researchers then used this data to create the interactive program “CityTree”. Authorities and hobby gardeners can use the online tool to analyze the tree population in their municipality or garden and plan new plantings free of charge. In the model, users can choose between twelve tree species of different sizes, 34 cities and various other location factors such as soil conditions and light incidence. They can also compare current and expected future climate conditions. The program then determines how much CO2 the tree can bind at each location, how much it cools its surroundings and how much water it uses. This makes it easier to find the most suitable tree.
Plane trees for Berlin, linden trees for Munich
The results show that not every tree is equally suitable for every city. The data shows, for example, that warm cities with little rain – such as Berlin or Würzburg – should plant tree species such as plane trees, maples or ash trees because they can withstand drought better. Wetter cities with comparatively high rainfall, such as Munich, can also plan for tree species such as small-leaved linden and horse chestnut, provided there is enough space for them.
When it comes to urban planning, the most important thing is to start early, the team stresses. “A tree has to grow for many years before it has a significant impact on the city’s climate,” says Rötzer. By the time a newly planted city tree today has grown large enough, the climate will most likely have worsened further. “There is therefore a lot of pressure to take a critical look at the trees in your city now and not just decide on tree planting based on aesthetic criteria,” says Rötzer. With “CityTree,” cities and municipalities now have concrete scientific information at their disposal to plan their greening for the future and prepare themselves as best as possible for climate change.
Source: Technical University of Munich, “CityTree”