A new study finds urban greening ‘not a panacea’ for dealing with extreme weather

Scientists suggest that urban greening is unlikely to provide the ‘single fix’ for tackling extreme weather events brought on by climate change.

Researchers at Cardiff University have led a team in a study which has shown that many cities around the world will not be able to reduce instances of heatwaves and flooding simply by introducing strategies such as green roofs, living walls, vegetated urban spaces and parks.

The team from Cardiff University in conjunction with scientists from the University of New South Wales, Karlsruhe Institute of Technology and Nottingham Trent University have published their findings in the journal Nature Communications.

They show that the cooling or flood-reducing potential of green urban spaces depends strongly on the prevailing climate of the city in question, with flood protection likely to be more successful in arid environments, whilst a cooling effect more likely in more humid climates.

With climate change increasing the likelihood and severity of extreme weather events in the future, significant risks are posed by the unique climates within urban areas.

The study found that city heatwaves can be attributed to the urban heat island effect (UHI), caused by the predominance of concrete and steel that absorb and retain heat, and the lack of cooling by water evaporating from plants.

Flooding is part of the urban stream syndrome (USS), whereby city structures and systems negatively affect the natural runoff of rainwater back into the environment.

To tackle these problems, a commonly proposed strategy is to implement urban greening in our cities in the form of green roofs, living walls, vegetated urban spaces or parks.

Not only can these measures reduce the UHI and USS effects in our cities, but they can also support local wildlife, reduce pollution and improve the general wellbeing of local populations.

Mitigation

The team also found that increasing variability in rainfall patterns due to climate change may reduce the performance of thinner green structures, such as green roofs, more quickly compared to larger greened areas with thicker soils and root systems.

Lead author of the study Dr Mark Cuthbert, from Cardiff University’s School of Earth and Environmental Sciences, said: “Our research found that the ability of urban greening to mitigate local flooding and excess heat is not automatic nor, in some areas, even possible,”

“Local and regional climatic conditions significantly impact the capacity of urban soils and plant growth to simultaneously defend against flooding and extreme heating. In fact, our findings indicate that in many, possibly the majority, of global cities, urban greening will not be able to mitigate cooling and flooding at the same time.”

“While urban greening may not be a panacea, our results show what’s possible in designing the cities of the future,” Dr Cuthbert concluded.

The team hope that by considering the findings, urban planners will be able to find the best solution for each individual city, and find a balance between performance, cost and viability.