An interactive map in Berlin is helping volunteers keep street trees alive during increasingly hot summers by showing exactly which ones need watering. The Gieß den Kiez project, which translates to “water your neighbourhood”, tracks more than 900,000 trees across the city and calculates each one’s water needs based on age, species and local rainfall.
The real-time watering data sets the project apart from other tree maps worldwide and allows volunteers to coordinate on a city-wide level. Users can see the last time a tree was watered, log a new watering, and colour-coding indicates trees in critical need. Saplings, for example, lack the mature root networks of older trees and require more frequent watering to survive. The platform also offers advice on correct watering techniques, collecting rainwater and the location of Berlin’s water pumps.
Volunteers and their adopted trees
Amanda Gläser-Bligh, a Berlin resident, adopted an eight-year-old street tree outside her door in Charlottenburg and named it “Linda the linden”. During hotter months, she carries about 20 litres of water to the tree once a week, a task that takes a couple of trips up and down stairs with a watering can. She has noticed the tree is no longer wilting in the summer heat.
“It feels very fun, almost like a video game,” Gläser-Bligh says. “I think many people may want to water the trees, but they might feel weird about doing it or they’re not sure if it’s their responsibility. But, if you have this app encouraging you, you know it’s the right thing to do.”
Linden trees are a hallmark of Berlin, lending their name to Unter den Linden boulevard. Their mature, dense canopies offer essential street cooling, while their blooms provide vital nectar for local bees.
Community action during heatwaves
The Gieß den Kiez project has been running since 2020 and currently has 12,000 registered volunteers. Their efforts complement those of district street and green space authorities, which already water thousands of trees but cannot always keep up during Berlin’s increasingly hot summers.
Anna Mehrländer, who has led the project for more than a year, says she was surprised at how deeply people care about trees. “Climate change is happening on our doorsteps. But watering a tree is a small action that helps your neighbourhood cope as summers get hotter. It also creates community at a time when people are increasingly working from home and on their phones all day.”
The biggest annual peak in tree waterings came just after the platform launched in 2020 at the start of the Covid pandemic, when nearly half a million litres were poured. Mehrländer believes this was because watering trees gave people a reason to get back outside and connect with nature. Waterings also rise during heatwaves: on 27 June, when Berlin experienced an all-time record high of 39.9C (103.8F), people poured 8,000 litres of water over trees across the city.
Trees as critical infrastructure
Studies show trees cool the air and break up urban heat islands during heatwaves, while reducing the risk of flooding during downpours. They also increase biodiversity, reduce air pollution and can improve mental health.
Urban forestry expert Dr Cecil Konijnendijk has proposed a 3:30:300 rule of thumb for greening cities: every citizen should be able to see at least three trees from their home, have 30% tree-canopy cover in their neighbourhood, and not live more than 300 metres from a park or green space. “In the past, trees were thought of as a nice aesthetic element in cities,” he says. “But now we’re starting to see them as critical infrastructure.”
Konijnendijk supports citizen initiatives like Gieß den Kiez and highlights the importance of soil volume and underground space for healthy root systems. “It takes 30 to 40 years before a new tree starts delivering the ecosystem services of a mature one… But a lot of trees are now being pushed to their limits during increasingly hot summers – drought is a big issue.”
The open-source nature of Gieß den Kiez means the map can be adopted by any city in the world. Residents in Potsdam, Leipzig, Magdeburg, and the 17th arrondissement of Paris have already launched their own versions. “Anyone can copy the code and set up their own Gieß den Kiez,” Mehrländer says. “The main requirement is a data set of all the trees in your city. It’s possible to replicate anywhere, from China to the UK.”
Back in Charlottenburg, Gläser-Bligh recently spotted someone else using the map to water a tree on the other side of her local park. “It’s a small step, a very small step,” she says. “But it has a direct climate impact.”
