'Build parks to climate proof our cities'

Scientists looking at the effect global warming will have on our major cities say a modest increase in the number of urban parks and street trees could offset decades of predicted temperature rises.

The University of Manchester study has calculated that a mere 10% increase in the amount of green space in built-up centres would reduce urban surface temperatures by as much as 4°C.

This 4°C drop in temperature, which is equivalent to the average predicted rise through global warming by the 2080s, is caused by the cooling effect of water as it evaporates into the air from leaves and vegetation through a process called transpiration.

"Green space collects and retains water much better than the built environment," explained Dr Roland Ennos, a biomechanics expert in Manchester’s Faculty of Life Sciences and a lead researcher in the team.

"As this water evaporates from the leaves of plants and trees it cools the surrounding air in a similar way to the cooling effect of perspiration as it evaporates from our skin."

Taking Greater Manchester as their model, the team used Geographic Information System (GIS) mapping to build up a picture of the conurbation’s land use. The team then worked out the impact that increasing the amount of green space would have on the urban climate as well as on water retention.

"Urban areas can be up to 12°C warmer than more rural surroundings due to the heat given off by buildings, roads and traffic, as well as reduced evaporative cooling, in what is commonly referred to as an ‘urban heat island’," said Dr Ennos, who worked on the project with Professor John Handley and Dr Susannah Gill in the School of Environment and Development.

"We discovered that a modest increase of 10% green space reduced surface temperatures in the urban environment by 4°C, which would overcome temperature rises caused by global warming over the next 75 years, effectively ‘climate proofing’ our cities.

"Such a reduction has important implications for human comfort and health within urban areas and opportunities need to be taken to increase green space cover wherever structural changes are occurring within urban areas, as well as planting street trees or developing green roofs."

The research, published in Built Environment also examined the effect increased green space would have on the amount of rainwater urban areas capture and retain; towns and cities lose a large proportion of rainwater through what is termed ‘run-off’ where precipitation quickly leaves the surface and drains away into streams and rivers, eventually returning to the sea.

"By the 2080s, our summers will be hotter and drier but winters are predicted to become wetter," said Dr Ennos. "An extreme wet winter’s day by the 2080s will deliver almost 50% more rain than is currently experienced.

"Based on an existing model, we have calculated that these more powerful storms would increase the amount of run-off from urban areas by more than 80%. Unfortunately, increasing the amount of green space only has a limited effect in reducing run-off and so flash flooding will become an increasing problem in our cities.

"Conversely, the warmer, drier summer months will reduce the amount of water available to plants and, during the longer droughts, this will reduce transpiration with its associated cooling effect.

"In order for the cooling effect of green spaces to work when it is most needed, cities would need to develop ways to store additional water, which could then be used to irrigate the green spaces during drier months."

Source: University of Manchester

Related stories:

A really inconvenient truth: Divorce is not green
The data are in. Divorce is bad for the environment. A novel study that links divorce with the environment shows a global trend of soaring divorce rates has created more households with fewer people, has taken up more space and has gobbled up more energy and water.
Cuter scooter defined by electricity, portability
It's energy efficient, it's clean, compact and simple, and, above all, it's very cool.
Ecologists discover city is 'uber-forest' for big owls
It may be news to its bankers, but Charlotte, the biggest city in North Carolina and a major center of the American financial industry, is actually an old growth forest. At least that’s the way the barred owls see it.
New invention may allow thirsty crops to signal farmers
Corn and potato crops may soon provide information to farmers about when they need water and how much should be delivered, thanks to a University of Colorado at Boulder invention optioned to AgriHouse Inc., a Berthoud, Colo., high-tech company.
Superconductivity Project Addresses Urban Power Challenges
Twenty thousand households in suburban Columbus, Ohio, are about to receive electricity through a high temperature superconducting cable developed at the Department of Energy's Oak Ridge National Laboratory.
Largest crater discovered in Sahara
Boston University researchers have discovered the remnants of the largest crater of the Great Sahara of North Africa.
Home IQ: Winning technologies will make people smarter -- not their houses
Someday, we may be getting fashion advice from our mirrors. Instead of digging through our closets to find the perfect complement for a new shirt, we may hold it up to our bedroom mirror for a computer to scan. Using radio-frequency identification technology, our electronic fashion stylist will then offer suggestions based on what's in our closet or how the latest edition of Vogue or Teen Beat pairs up something similar.
Eyes turn to dawn of 'visual computing'
Lifelike graphics are breaking free of elite computer games and spreading throughout society in what industry insiders proclaim is the dawning of a "visual computing era."

News discussion:

Space & Earth science news