Climate Square at the Southern Portal of Karlsruhe Central Station by bauchplan ).(

Let It (D)rain, Sponge It In

Sustainable Square at the Southern Portal of Karlsruhe Central Station

Mobility transition, climate crisis, and demographic change – these pressing challenges have long since arrived in our cities. The newly redesigned station square at the southern entrance of Karlsruhe’s main train station responds with a clear vision: a place where transfers between train, long-distance bus, bicycle, Kiss+Ride, and taxi are simple and pleasant. At the same time, the square functions as a green urban space inviting people to linger – whether while waiting for the next train or during a lunch break. The design, which emerged from a planning competition, shapes the square both functionally and atmospherically. It complements the northern station square and sets a strong example of sustainable urban design as a “green gateway” and landmark.

A Square with Unique Challenges
The surrounding area presented specific challenges: the square lies directly in front of the historic station building, is flanked by outdated glass high-rises, is built almost entirely over an underground parking garage, and is exposed to intense sunlight. As early as the 2019 competition, it was clear: a square must be created here that offers a pleasant climate despite these conditions – the square as a green showcase for the city.

Green Spaces, Water Features, and Climate-Resilient Trees
The design is based on an analysis of pedestrian flows, usage needs, and a climate simulation. This resulted in a clear structure: two groups of trees – comprising a total of 25 climate-resilient species – flank the recreational areas on either side of the station entrance. These areas include long benches and bicycle racks. A water feature provides cooling, adjusting its intensity based on sunlight and offering playful interaction. It also creates a soft boundary for vehicular traffic, which is still permitted only along the southern edge of the square (e.g., for taxis and Kiss+Ride).

A Square That Works with the Climate
As you exit the station passage, the square opens up like a green oasis: the trees provide shade, cool the air through evaporation, and protect against downdrafts between the high-rises – creating a pleasant microclimate year-round.

Even though the square is almost entirely built over an underground parking garage, rainwater is purposefully collected: the gentle topography channels water into an underground “sponge body” with a capacity of 1,200 m³. From there, it is delivered to the trees – in line with the sponge city principle, yet customized for the specific urban character of the site.

As part of a blue-green infrastructure, the surface paving in the resting zones is perforated with grass joints, allowing water to seep through and be directed via a system of partial infiltration pipes into a continuous root zone — with up to 1.5 meters of coverage over the underground garage. Integrated inspection shafts ensure ease of maintenance, allow scientific monitoring, and handle emergency overflow to ensure disaster resilience, enabling the square to absorb even 100-year extreme rainfall events.

Light and Atmosphere
Specially developed light poles penetrate the tree canopy in a playful arrangement, meeting high standards for glare-free lighting while harmonizing atmospherically with the vegetation. Even by day, they act as important visual markers — visible from the train.

A Resilient Urban Component
In everyday urban life, the plaza offers visitors a place where people can easily find their way, transfer comfortably, and relaxation. With its integrated water management, its contribution to the urban climate, and its distinctive character, it offers the new urban district a strong sense of identity – as a green oasis with new resilience against heavy rain events and heatwaves.

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