Enlarge image
Extremely sealed, extremely hot: promenade in Hamburg's new HafenCity district
Photo: IMAGO/Christian Ohde
Is green really worth less than stone?
Or does maintaining or investing in new green spaces in cities pay off after all?
These questions are now to be answered by the online tool »Valuing Urban Green«, which the environmental economist Jesko Hirschfeld from the Berlin Institute for Ecological Economy Research has developed together with scientists from the Humboldt University and German partner cities.
The tool, co-financed by the Federal Ministry of Research, calculates the value of urban greenery in euros - by avoiding costly climate impacts and by improving the quality of life.
The »Valuing City Green« tool is available in a very detailed version for experts and specialist agencies.
From August, a slightly slimmed-down version will be publicly accessible, showing the climate impacts of various green scenarios for 23 German cities.
SPIEGEL:
Mr. Hirschfeld, your tool “Valuing City Green” calculates the benefits and value of city green in euros.
For what purpose?
Hirschfeld:
We want to make the value of urban greenery tangible.
On the one hand, it consists of ecosystem services such as rainwater retention, climate regulation, binding of air pollutants.
On the other hand, it refers to the cultural dimension, i.e. to the recreational function or experience of nature for urban society.
If we put all this in euros, then this figure provides politicians with arguments for budget decisions.
SPIEGEL:
To do this, the number must be convincingly calculated.
What factors go into this?
Hirschfeld:
We determine how many kilograms of specific air pollutants are held back by trees or how many cubic meters of water the urban green absorbs compared to sealed areas.
And what influence additional green has on the temperature.
This is based on very differentiated model calculations.
The Humboldt University in Berlin has made simulations of the microclimate, some of which are accurate to a range of two by two meters.
In concrete case studies, it can be determined in great detail how much cooling a green roof, a small unsealed area or even a single tree creates.
SPIEGEL:
And how do you determine the cultural value?
Hirschfeld:
In a nationwide study, we asked 8,000 people how much they would personally pay for more urban green spaces each year.
There are other factors, too, such as the savings in healthcare that come from reduced pollutants or lower temperatures.
SPIEGEL:
People's willingness to pay for nature experiences and recreation seems rather low.
According to your study, in the central districts of Berlin it is four euros per person per year for one percent more green space.
That's not even three scoops of ice cream.
Hirschfeld:
That is by no means small.
In total, around 3.7 million Berliners raise a lot of money.
If we also factor in the savings in healthcare, the converted carbon dioxide and all the other factors, then even modest increases in urban greenery add up to tens of millions.
Per year.
And when we talk about the metropolises, we end up with amounts in the hundreds of millions.
Parks departments can only dream of such budgets today.
SPIEGEL:
The modellers at Humboldt University have determined what cooling can be achieved with different measures for three test areas of your tool in Leipzig, Karlsruhe and Berlin.
What was the result?
Hirschfeld:
That trees have the greatest effect because they create a lot of shade, so streets and sidewalks are protected from the sun and don't heat up as much.
By planting new street trees, such as in Kurt-Eisner-Strasse in Leipzig, the perceived temperature in the street area can be reduced by up to 10 degrees.
We were also surprised how effective the unsealing of parking lots or backyards is, for example.
Open green spaces can store a lot of water and have a cooling effect through evaporation.
A facade greening affects the climate in the streets only slightly, but reduces the heating of the building.
And we have found that green roofs are effective because not only does it cool the roof, but the cooler air flows down and also lowers the temperature in the streets and courtyards.
Enlarge image
"Trees have the greatest cooling effect": The calculations by Humboldt University show the lower temperatures in blue, which are the result of denser planting of street trees.
SPIEGEL:
What do you mean by “green roof”?
A green roof can consist of bushes or even trees in raised beds, or low-level, extensive greenery.
Hirschfeld:
We actually only used extensive greening as a basis here, because this savings option has been the norm up to now.
Of course, an intensively greened, irrigated roof is ideal.
SPIEGEL:
Many buildings don't even have a flat roof that could be planted with greenery.
Hirschfeld:
Some old buildings have gabled roofs that also have flat areas.
And there is an enormous amount of flat roofs, mainly covered with tar paper, especially on commercial buildings, post-war buildings and garages.
Thousands of hectares of greenery could be created here.
But the green on the ground is much more important.
SPIEGEL:
You need space for that, and that's scarce in the cities.
Hirschfeld:
If you do without parking spaces or lanes, you can create green strips there.
If you want to get parking spaces, you can replace the asphalt with grass pavers.
Courtyards can be unsealed.
All this would immediately increase the quality of living, because the microclimate improves significantly.
Interestingly, after the war, some places planned much more progressively.
Enlarge image
Rothenburgsort district of Hamburg: In the district that was created on a wasteland from the war, the blocks of houses are surrounded by green spaces and trees
Photo: imageBROKER/Thomas Robbin / imago images/imagebroker
SPIEGEL:
What do you mean by that?
Hirschfeld:
The buildings that were erected in the 1950s and 1960s on large brownfield sites often stood very loosely and were surrounded by green spaces with trees.
On the other hand, if you look at the HafenCity development area in Hamburg, then practically everything there is sealed.
I find it amazing how little green this young neighborhood has gotten.
That is very daring at a time when climate change is already here.
(The SPIEGEL climate report - the latest developments, research results and background information on the climate crisis as a newsletter: every week directly in your e-mail inbox.
Register now
.)
SPIEGEL:
You tested “Valuing urban greenery” in three cities.
Did the findings also result in concrete measures?
Hirschfeld:
Our research has strengthened planning for more green in the city.
In Karlsruhe, for example, we looked at the inner city east.
Against the background of our investigation results, the city has now passed a so-called green statute.
In the development plan, conditions are made to secure and expand green structures.
In addition, the number of street trees is to be increased further.
Karlsruhe has been trying to increase greenery for a long time, but we have now provided reliable figures that support the arguments for more greenery.
Berlin and Leipzig are also working on expanding the urban green space.
Enlarge image
Young street trees on Kurt-Eisner-Strasse, Leipzig, in 2006
Enlarge image
Kurt-Eisner-Straße in 2016: Densely grown, shady avenue
SPIEGEL:
Climate change means that existing urban green areas are having a hard time because of the increasing drought.
What needs to be done here?
Hirschfeld:
In Berlin we looked at a part of Neukölln that also includes the Volkspark Hasenheide.
A concept is currently being developed here as to how Hasenheide can be redesigned to be climate-resilient.
Such adjustments are urgently needed because thousands of trees are at risk of drying out.
In Berlin, however, it is now stipulated in new development areas that rainwater may no longer be drained into the sewage system, but must seep away on the area.
SPIEGEL:
You want to put your tool for evaluating urban green spaces online in August – what can a layperson or specialist do with it?
Hirschfeld:
We have made our results for 23 major German cities easily accessible in the Stadtgrün online tool.
You can easily set scenarios using sliders, for example more street trees in Augsburg, more green spaces in Dortmund, green paths in Hamburg or more green roofs in Munich.
At the push of a button, the tool then calculates the effects on, among other things, water retention, air pollution control, the appreciation of the city population and gives an estimate of the effect on the city climate.
On a city map you can see where the respective effects are to be expected and the overall values are shown in a table.
The overall benefit quickly amounts to well over fifty million euros per year.
We want to use this to provide information for a well-founded discussion about city-wide strategies that create more green spaces.
SPIEGEL:
Doesn't your tool also prove that in the end it's always all about the money?
Hirschfeld:
In any case, money is very much the focus of attention for many decision-makers in urban policy, and that is actually quite sad.
Unfortunately, when it comes to climate change, all parties still pay more lip service than responsible action, to varying degrees.
When the going gets tough when it comes to budgetary decisions, the focus is still mostly on short-term economic effects, such as commercial settlements, housing construction.
Green spaces and street trees are only perceived as a cost factor.
That's why we want to underpin the climate arguments with monetary values.
SPIEGEL:
Maybe you don't have to build on every square meter that you could build on, and instead reserve areas for greenery and biodiversity.
Hirschfeld:
That's always the question: Where and how do you create living space?
Newly built neighborhoods on the outskirts are also not good, because commuter traffic adds to the land use.
One solution is to convert existing buildings or to use existing buildings more efficiently, since the cities are already densely built up.
If you look closely, cities have an enormous reservoir of areas that could be greened.
Building on green areas, allotments or unsealed wasteland is the worst thing you can do today.
SPIEGEL:
Then politicians would probably have to say goodbye to one or the other favorite project.
Hirschfeld:
Yes!
In Berlin, with the approval of the red-green-red government, a city freeway is being built, this is madness in terms of transport policy and climate policy!
But there is also the everyday insanity of the authorities: In some cities there are still parking space ordinances that stipulate the construction of parking spaces.
And urban greenery is also a socio-political issue, and that too hardly gets any attention.
MIRROR:
To what extent?
Hirschfeld:
On the one hand, it is mostly the less well-off who live in the worst environmental situations in the cities, namely on the noisiest and busiest streets and in neighborhoods with the least amount of green space.
On the other hand, greening makes the quarters more beautiful and attractive, also for investors.
You have to be very careful that price increases don't push out the people you wanted to make life more comfortable for.
The federal government would have to act here to stop real estate speculation.
SPIEGEL:
How could each individual strengthen urban green spaces and appreciate them more?
Hirschfeld:
There are many possibilities: You can support the planting of new street trees by sponsoring a tree or simply water the tree in front of your own front door.
You can put climbing plants on the facade, plant the roof or the balcony.
Under no circumstances should you fill your own garden with crushed stone or gravel and also not buy a robotic lawnmower, but rather let a biodiverse wildflower meadow grow that is only mowed twice a year.
Or you can get involved in a citizens' initiative that works to convert parking spaces into green spaces or that protects healthy old trees from being felled.
Old trees are very difficult to replace.
Trees take half a century to fully develop.
We don't have that much time anymore.