Researchers discover simple factor that can improve cities in multiple ways: 'We wanted to understand'

Planting more trees in urban areas can lower street temperatures, prevent flooding, and even improve mental health, according to a new study published in Scientific Reports.

The researchers also found that including a greater diversity of tree species enhanced some of these benefits.

"We wanted to understand how people choose public parks, and what role the structure and composition of urban and peri-urban forests play in this choice," said study co-author Somidh Saha, per Earth.com.

What the researchers discovered could transform the way we think about the presence of trees in urban spaces.

Working at the Karlsruhe Institute of Technology in Germany, Saha and his colleagues used complex hydro-climatology models to "evaluate the impacts of urban greening during extreme heat and rainfall events."

With the city of Karlsruhe, Germany as their subject, the researchers investigated the impacts of adding 30% additional tree cover.  

Regarding extreme heat, the study revealed that the increased green canopy would decrease the number of hours spent in extreme heat, defined as hotter than 88 degrees Fahrenheit, by nearly two-thirds.

Trees' ability to mitigate high temperatures comes from the shade they provide as well as the cooling effects of wet soil, according to the study.

Anyone who has ever had a hard time falling asleep on a hot night will be happy to hear that the trees' impact continued into night, with the reduced surface heat buildup during the day resulting in temperatures up to 10 degrees Fahrenheit cooler from midnight to sunrise. 

As for extreme rainfall events, the researchers found that increasing green spaces reduced runoff across city districts by an average of 58%, with dry-soil conditions prior to the storm reducing runoff by an additional 10%. 

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The benefits did not end there. 

Using social surveys, Saha and the other researchers observed that people achieved higher satisfaction in parks where they perceived the diversity of trees to be higher. 

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

The findings confirmed the results of other research showing the significant mental health benefits of spending time in green spaces.

A separate study found that people spending a total of just two hours per week in nature — including parks — described themselves as having significantly better health and well-being than those who spent no time in green spaces.

In addition to advocating for more parks and green spaces in your community, there are many things that you can do to incorporate these findings into your own home. 

For example, replacing your old-fashioned monoculture lawn with a natural lawn or native garden will increase the diversity of plants in your yard while also saving you money on your water bill and landscaping costs.

Going even further and completely rewilding your yard would benefit your household's mental health while also providing food and shelter for local wildlife, from pollinators to birds to small mammals.   

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