KARLSRUHE, Germany — Cities that expand and diversify their urban forests can sharply reduce heat stress, limit flooding and boost residents’ quality of life, according to two studies from the Karlsruhe Institute of Technology (KIT). Published in Sustainable Cities and Society and Scientific Reports, the projects examined how tree diversity influences park use and how larger canopies affect microclimate and hydrology in Karlsruhe, Germany.
In surveys of park users, most respondents said they felt most comfortable in areas they perceived as having a high variety of tree species. The finding suggests that incorporating a broad mix of trees can make public green spaces more attractive and support public health goals.
Separate modeling of five years of rainfall and temperature data showed the infrastructure benefits of a larger canopy. Simulating an increase of at least 30 percent in tree cover, researchers found that extreme-heat hours could fall by nearly two-thirds while stormwater runoff could drop by more than half.
“We can show that increasing the number of trees by at least 30 percent could reduce the number of hours per year of extreme heat by nearly 64 percent and the amount of runoff by 58 percent, so trees can strengthen resistance to heat and flooding, especially in districts with high building density,” Saha said.
The work gives local governments data to support tree-planting initiatives aimed at climate resilience and resident well-being. KIT notes that tree-rich parks also filter air pollutants and provide recreational space — benefits that become more critical as extreme weather events intensify. Researchers plan further studies to explore the direct links between specific tree species, canopy structure and human health outcomes.
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