Urban greening 'not a panacea' for dealing with extreme weather

Date:
January 26, 2022
Source:
Cardiff University
Summary:
Urban greening is unlikely to provide a single fix for tackling
extreme weather events brought on by climate change, scientists
have suggested.



FULL STORY ========================================================================== Urban greening is unlikely to provide a single fix for tackling extreme
weather events brought on by climate change, scientists have suggested.


==========================================================================
A team led by researchers from Cardiff University has shown that the
majority of cities around the world will not be able to reduce instances
of heatwaves and flooding at the same time through the introduction of strategies such as green roofs, living walls, vegetated urban spaces
and parks.

Publishing their findings today in the journal Nature Communications,
the team 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.

Urban areas each have unique climates that pose significant risks,
even more so as climate change increases the likelihood and severity of
extreme weather events in the future.

Heatwaves within our cities 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,
they can also support local wildlife, reduce pollution and improve the
general wellbeing of local populations.

In their study, the team used global climate model outputs and weather information from 175 cities around the world spanning 15 years of daily observations, from 2000 to 2015.

This data was used in conjunction with theories taken from soil science
to calculate water infiltration into soils, which act like a sponge
to reduce rainwater runoff, and the evaporation of water from plants,
which can induce the desired cooling effect.

"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," said lead author of study Dr Mark Cuthbert, from Cardiff University's School of Earth and Environmental Sciences.

"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."
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.

They say these things must be considered by urban planners in order to
find the best solution for each individual city, with a balance needed
between performance, cost and viability.

"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 research was led by Cardiff University in conjunction with scientists
at the University of New South Wales, Karlsruhe Institute of Technology
and Nottingham Trent University.

========================================================================== Story Source: Materials provided by Cardiff_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. M. O. Cuthbert, G. C. Rau, M. Ekstro"m, D. M. O'Carroll,
A. J. Bates.

Global climate-driven trade-offs between the water retention and
cooling benefits of urban greening. Nature Communications, 2022;
13 (1) DOI: 10.1038/s41467-022-28160-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220126090510.htm

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