Bronagh McCarron

Cooling Berlin: Enhancing Evapotranspiration Through Wind-Aligned Design

Initially, when looking at this project, I took a developmental approach, introducing new housing blocks, a school and a daycare. Through developing this idea, I came to the conclusion that it was not the correct fit for the site. Tempelhofer Feld is a unique, vast open space within the city and is defined by its character and history. Having visited the site in late January, it is clear that the site is used all year round for recreational purposes. The locals respect it and understand its importance. Although there is a housing crisis, development on Tempelhofer Feld is not the answer; such an important space should be preserved. This caused me to change direction in my project and take a climate action approach.  

2025 was the hottest year, it was the 2nd consecutive year of unprecedented global heat. This heat contributed to severe climate impacts, including wildfires, extreme heat and heavy rainfall events. The global temperature exceeded the critical 1.5°C threshold set by the Paris Agreement. NASA reported the Earth's surface temperature was approximately 1.28°C above its 20th-century baseline. Berlin faced increased tropical nights, up to 15 annually in central Berlin, which is projected to double by 2050 if nothing is done.  

This project enhances evapotranspiration through multilayered planting and drought-tolerant planting with high leaf area indices. Simultaneously creating wind corridors aligned with prevailing winds to maximise passive cooling, improve air quality, mitigate the urban heat island effect and support biodiversity while maintaining the site's character. 

Evapotranspiration is the process by which plants release water vapour, which leads to the cooling of the surrounding area. Evapotranspiration can reduce peak summer air temperatures by 1-5°C. By designing in layered planting featuring canopy cover, understory shrubs and groundcover, evapotranspiration can be enhanced greatly. Having more layers results in more leaves, which creates more transpiration, therefore more cooling. Leaf area index must be considered when choosing plants, as the higher the LAI, the higher the cooling potential. A canopy cover with broad, dense leaves creates deep shade while shrubs and groundcover planting create a synergistic cooling effect. Diverse planting also has ecological benefits, such as enhancing biodiversity on site. 

Strategically planting the trees in line with prevailing winds allows for the funnelling of cool air into the surrounding urban area. Wind tunnels are a long-term cooling strategy, making them essential for future-proofing spaces such as Tempelhof. Trees should be planted in rows with adequate spacing to allow for wind flow. Coppicing the trees maintains airflow while boosting leaf production, and combining this with understory planting amplifies both cooling and corridor function.  

This project sees Tempelhofer Feld as a climate-critical site. Through layered planting and wind-aligned design, this project enhances cooling, supports biodiversity and acts as a model for adapting open spaces to a future of rising temperatures, while preserving the unique character that makes it so vital to Berlin.