Planting certain kinds of trees can make cities hotter at night, not cooler, according to a new study. Trees can significantly reduce the temperature of cities during the day by providing shade, changing the airflow and through the evaporation of water from microscopic pores in their leaves.
But a new study has found that tree canopies can trap heat, closing those pores in response to heat and drought stress, leading to higher temperatures at night. The research, published on Tuesday in peer review journal Communications Earth & Environment, found that urban trees can bring surface temperatures down by as much as 12°C. But that cooling ability is heavily dependent on the species, urban layout and climate.
In heavily built-up and dry cities like Dubai, trees cool the air more, Dr Ronita Bardhan, associate professor of Sustainable Built Environment at the University of Cambridge, told The National. They take the water in the air into their leaves through their pores, using it to perform photosynthesis, where they convert light into chemical energy.
"If you’re sweating and standing under a tree, the sweat is taken up by the air into the leaves and the leaves then use that to perform their photosynthesis function. That’s why you feel cooler," said Dr Bardhan. But at night, the microscopic pores in trees' leaves close. "Where it closes down, the heat below it is trapped. It is no longer able to escape."
In arid climates, air has less water, so trees take up less water. Whereas in a very humid area, even after the trees had taken a lot of humidity to do their evapotranspiration process, there is still water remaining, said Dr Bardhan. The study "busts the myth that trees are the ultimate panacea for overheating cities across the globe”, she added.
“Trees have a crucial role to play in cooling cities down but we need to plant them much more strategically to maximise the benefits which they can provide.”
In tropical wet and dry climates, trees cool cities in countries such as Nigeria by as much as 12°C during the day, but heat the area around them at night by up to 0.8°C. In arid climates, including the UAE, trees cooled cities by around 9°C in daytime, warming them at night by 0.4°C.
Ghaf trees – in pictures
In tropical, humid climates, the daytime cooling effect dropped to 2°C, with 0.8°C warming at night. In temperate climates, trees can cool cities by up to 6°C and warm them by 1.5°C. Urban environments are more likely to feature a variety of evergreen and deciduous trees of different sizes – a mix that tends to result in greater cooling in temperate, continental and tropical climates, according to the study.
Using a variety of trees in these climates generally results in 0.5°C more cooling than in cities which only have deciduous or evergreen trees. Researchers said this is because mixed trees can balance seasonal shading and sunlight, providing three-dimensional cooling at various heights.
However, in arid climates, evergreen species dominate and cool more effectively in cities like Cairo and Dubai. Popular evergreen species in the UAE include the national tree – the ghaf – scientific name prosopis cineraria – which typically lives for 120 years. It was traditionally used to feed livestock and was revered for its purported medicinal properties.
In open urban layouts, cooling can be improved by about 0.4°C because their larger green spaces allow for more and larger tree canopies and a greater mix of tree species, the study said.
“Our study provides context-specific greening guidelines for urban planners to more effectively harness tree cooling in the face of global warming,” Dr Ronita Bardhan said.
“Our results emphasise that urban planners not only need to give cities more green spaces, they need to plant the right mix of trees in optimal positions to maximise cooling benefits. Urban planners should plan for future warmer climates by choosing resilient species which will continue to thrive and maintain cooling benefits,” she added.
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French business
France has organised a delegation of leading businesses to travel to Syria. The group was led by French shipping giant CMA CGM, which struck a 30-year contract in May with the Syrian government to develop and run Latakia port. Also present were water and waste management company Suez, defence multinational Thales, and Ellipse Group, which is currently looking into rehabilitating Syrian hospitals.
Zayed Sustainability Prize
The five pillars of Islam
Dr Afridi's warning signs of digital addiction
Spending an excessive amount of time on the phone.
Neglecting personal, social, or academic responsibilities.
Losing interest in other activities or hobbies that were once enjoyed.
Having withdrawal symptoms like feeling anxious, restless, or upset when the technology is not available.
Experiencing sleep disturbances or changes in sleep patterns.
What are the guidelines?
Under 18 months: Avoid screen time altogether, except for video chatting with family.
Aged 18-24 months: If screens are introduced, it should be high-quality content watched with a caregiver to help the child understand what they are seeing.
Aged 2-5 years: Limit to one-hour per day of high-quality programming, with co-viewing whenever possible.
Aged 6-12 years: Set consistent limits on screen time to ensure it does not interfere with sleep, physical activity, or social interactions.
Teenagers: Encourage a balanced approach – screens should not replace sleep, exercise, or face-to-face socialisation.
Source: American Paediatric Association
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Disability on screen
Empire — neuromuscular disease myasthenia gravis; bipolar disorder; post-traumatic stress disorder (PTSD)
Rosewood and Transparent — heart issues
24: Legacy — PTSD;
Superstore and NCIS: New Orleans — wheelchair-bound
Taken and This Is Us — cancer
Trial & Error — cognitive disorder prosopagnosia (facial blindness and dyslexia)
Grey’s Anatomy — prosthetic leg
Scorpion — obsessive compulsive disorder and anxiety
Switched at Birth — deafness
One Mississippi, Wentworth and Transparent — double mastectomy
Dragons — double amputee
65
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Engine: 4.0-litre, six-cylinder
Transmission: six-speed manual
Power: 395bhp
Torque: 420Nm
Price: from Dh321,200
On sale: now
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Lexus LX700h specs
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Power: 464hp at 5,200rpm
Torque: 790Nm from 2,000-3,600rpm
Transmission: 10-speed auto
Fuel consumption: 11.7L/100km
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Price: From Dh590,000
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JAPAN SQUAD
Goalkeepers: Masaaki Higashiguchi, Shuichi Gonda, Daniel Schmidt
Defenders: Yuto Nagatomo, Tomoaki Makino, Maya Yoshida, Sho Sasaki, Hiroki Sakai, Sei Muroya, Genta Miura, Takehiro Tomiyasu
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Groom and Two Brides
Director: Elie Semaan
Starring: Abdullah Boushehri, Laila Abdallah, Lulwa Almulla
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Total fights: 32
Wins: 28
Wins by KO: 26
Losses: 4
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The Penguin
Starring: Colin Farrell, Cristin Milioti, Rhenzy Feliz
Creator: Lauren LeFranc
Rating: 4/5
What are the influencer academy modules?
- Mastery of audio-visual content creation.
- Cinematography, shots and movement.
- All aspects of post-production.
- Emerging technologies and VFX with AI and CGI.
- Understanding of marketing objectives and audience engagement.
- Tourism industry knowledge.
- Professional ethics.
Mobile phone packages comparison
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Specs
Engine: 51.5kW electric motor
Range: 400km
Power: 134bhp
Torque: 175Nm
Price: From Dh98,800
Available: Now
The biog
Family: Parents and four sisters
Education: Bachelor’s degree in business management and marketing at American University of Sharjah
A self-confessed foodie, she enjoys trying out new cuisines, her current favourite is the poke superfood bowls
Likes reading: autobiographies and fiction
Favourite holiday destination: Italy
Posts information about challenges, events, runs in other emirates on the group's Instagram account @Anagowrunning
Has created a database of Emirati and GCC sportspeople on Instagram @abeermk, highlight: Athletes
Apart from training, also talks to women about nutrition, healthy lifestyle, diabetes, cholesterol, blood pressure
ETFs explained
Exhchange traded funds are bought and sold like shares, but operate as index-tracking funds, passively following their chosen indices, such as the S&P 500, FTSE 100 and the FTSE All World, plus a vast range of smaller exchanges and commodities, such as gold, silver, copper sugar, coffee and oil.
ETFs have zero upfront fees and annual charges as low as 0.07 per cent a year, which means you get to keep more of your returns, as actively managed funds can charge as much as 1.5 per cent a year.
There are thousands to choose from, with the five biggest providers BlackRock’s iShares range, Vanguard, State Street Global Advisors SPDR ETFs, Deutsche Bank AWM X-trackers and Invesco PowerShares.
Get Out
Director: Jordan Peele
Stars: Daniel Kaluuya, Allison Williams, Catherine Keener, Bradley Whitford
Four stars
Total eligible population
About 57.5 million people
51.1 million received a jab
6.4 million have not
Where are the unvaccinated?
England 11%
Scotland 9%
Wales 10%
Northern Ireland 14%
Sri Lanka-India Test series schedule
- 1st Test India won by 304 runs at Galle
- 2nd Test India won by innings and 53 runs at Colombo
- 3rd Test August 12-16 at Pallekele
