For decades, we’ve known that urban environments modify climate. The “heat island” effect caused by hard surfaces boosts city temperatures, and with global warming adding its contribution to heat woes, urban heat stress becomes a very real phenomenon.
Just as we see climate responsive buildings that can save energy on lighting, heating and cooling through clever design that works with the surrounding environment, so urban landscape architecture should be climate responsive. To achieve this, says Wieke Klemm, a researcher at Wageningen University in the Netherlands, landscape architects need situational knowledge of the specific location and its unique characteristics as well as general knowledge spanning a wide range of topics including methods to influence microclimate, promote biodiversity, and facilitate recreation.
What is Urban Green Infrastructure?
Klemm sees Urban Green Infrastructure as embracing the entire network of green spaces in urban environments. They include public and private gardens, street trees, and parks, and together, they provide ecosystem services to urbanized areas. The vision would be to design and manage these spaces so that they regulate city microclimates resulting in greater comfort and reduced thermal stress.
The Cooling Effect of Urban Greenery
Urban greenery has two broad impacts on thermal comfort. On an objective level, it reduces ambient temperatures and the physical stress associated with radiated light and heat. You could be up to 1.7° C cooler in a cluster of trees or under a tree with a large canopy.
When under smaller trees, the temperature isn’t lower, but you have the comfort of shade and reduced glare so you feel cooler. Meanwhile, the shaded and vegetated surfaces don’t absorb as much heat and won’t have as much heat to give off later on.
There’s definitely a subjective effect. It’s possible that we all perceive thermal comfort differently, but our behavior is certainly influenced by urban greenery and its microclimate-regulating effects. The simplest example is moving into the shade of a tree on a hot day.