Why trees make city people happier

By Stephen Beech

Trees make people happier in urban areas, according to a new study.

They also make towns and cities more climate-resilient, say scientists.

Two new studies, published in the journal Sustainable Cities and Society, looked at how urban greening affects microclimate, flood risk and the quality of city life.

In the FutureBioCity project coordinated by the Karlsruher Institute of Technology (KIT) in Germany, researchers investigated exactly how to design parks and other green spaces so that people feel especially comfortable there.

Study leader Dr. Somidh Saha said: “We wanted to understand how people choose public parks, and the role the structure and composition of urban and peri-urban forests play in this choice by."

The research team combined elements of ecological research with survey methods used in social sciences.

Most of the participants surveyed said they felt most comfortable in places where, in their own assessment, the diversity of trees was particularly high.

Dr. Saha said, “That shows that future parks should be designed to be as diverse and natural as possible so they appeal to people."

The research team plans to investigate further whether there is a direct correlation between well-being and the observed diversity of tree species.

In another project called GrüneLunge - "green lung" - Dr. Saha’s research group analysed how parks can promote rainwater seepage and heat mitigation in cities.

He said: “We investigated how much additional trees in cities can help to reduce flooding in extreme rainfall events by slowing down the draining water.”

The team also examined the extent to which trees can alleviate heat in cities.

The researchers analyzed rainwater drainage and heat generation in the city of Karlsruhe over a period of five years.

They then simulated various urban greening scenarios and analyzed their effects on the microclimate and hydrology.

Dr. Saha said: “We can show that increasing the number of trees by at least 30% could reduce the number of hours per year of extreme heat by nearly 64% and the amount of runoff by 58%, so trees can strengthen resistance to heat and flooding, especially in districts with high building density."

He added: "The results of the two projects show that diverse green spaces with trees can improve human health in cities and mitigate the negative effects of climate change, especially in the case of the extreme heat waves and heavy rainfall events that are expected to occur with increasing frequency due to human-induced climate change."