TEPIC, Mexico, Feb 15 (Thomson Reuters Foundation) - Rio de
Janeiro is sweltering in blazing temperatures as it gears up for
its spectacular carnival later this month, but in its northern
favelas, the mercury is spiking even higher as hot, tropical air
trapped in the narrow concrete alleys causes stifling conditions
and a potential rise in health problems.
Christovam Barcellos, coordinator of the climate and health
observatory at Brazil’s Fiocruz government health institute,
noted that on summer days, when the temperature is around 32
degrees Celsius (89.6°F) in Rio’s southern zone, it is 3 to 4
degrees higher in northern parts of the Brazilian city.
“It’s really significant - not only for mosquito-transmitted
diseases but also in terms of health for vulnerable people with
heart diseases (or) hypertension,” he said.
In cities across Latin America, haphazard development
combined with heat pumped out by cars, factories and buildings
is causing “urban heat islands”, where city temperatures are
higher than their surrounding areas.
Temperature differences are usually greatest at night when
stagnant warm air becomes trapped.
While daytime temperatures often differ by a few degrees
Celsius, some areas experience substantial spikes. In Rio’s
hottest suburbs, for example, temperatures can be as much as 20
degrees Celsius higher than around the city, said Andrews
Lucena, associate professor at Rio's Federal Rural University.
“This is a problem that’s going to become critical,” said
Jennifer Doherty-Bigara, climate specialist at the
Inter-American Development Bank.
“When we think about cities, we shouldn’t only think about
the economic opportunities. If we don’t have climate-friendly
cities, it will have an impact on the same productivity we’re
trying to foster,” she said.
While megacities such as Mexico City, Sao Paulo and Rio de
Janeiro have long been affected by the heat island effect, other
cities such as Santiago, Lima and Buenos Aires are now suffering
from it too, climate experts said.
Changing building design and materials, enhancing airflows
and simply planting trees could help make cities and their
residents more resilient to the urban heat island effect, which
can worsen pollution, boost energy demand and even curb economic
activity, said experts.
“We think of cities as a series of canyons with the streets
lined with buildings on either side so they are very efficient
in trapping the heat... You are bombarded by reflections and
re-re-re-reflections from every building around,” said Rohinton
Emmanuel, professor of sustainable design at Glasgow Caledonian
“Each of us is equivalent to a 100-watt bulb walking around,
and that generates more heat too,” he said, explaining that air
pollution can also stop heat escaping.
While specific data on Latin America is limited, a 2015
global study showed significant increases in urban heatwaves
over a 40-year period, alongside a fall in city winds, according
to its co-author Dennis Lettenmaier. Minimum temperatures are
rising quicker than maximum temperatures around the world,
causing more hot nights, he added.
Urban development is linked to this trend, although the
warming of the planet may be a larger contributor, said
Lettenmaier, a geography professor at the University of
“But if you don’t have air conditioning and you’re in a
major city and you get a big heatwave, does it really make a
difference to you why? Whether it’s city development or whether
it’s because of general global warming, it’s still a big
problem,” he added.
While high-rise city centres can generate their own heat
islands as glass sky-scrapers reflect the sun, block airflow and
pump out warm air from cooling systems, slum areas such as Rio’s
favelas can also become heat traps with their tightly packed
concrete-block houses and lack of trees.
The associated health risks include heat exhaustion, stress,
respiratory and cardiovascular problems, while higher pollution
levels are a particular threat to children and older people.
Scientists are also studying whether heat islands can expand
the spread of mosquitoes carrying dengue, Zika and chikungunya.
“The poorest people are always more affected,” said Massimo
Palme, associate professor at Chile's Catholic University of the
North, who has studied heat islands in Pacific coast cities.
“When a heatwave occurs, if they don’t have water supplies
(or) hospitals nearby, they are in danger much more than other
While persuading local governments to invest in
climate-related measures is tricky, experts say there are plenty
of cheap and effective options available.
Simply painting building and bus roofs white reflects heat,
as does planting shady trees which can also cut air pollution.
Promoting public transport over private cars, and offering tax
incentives for roof gardens are also recommended.
Longer-term, urban planners and architects should focus on
expanding green areas, using less glass and positioning
buildings to cut heat generation and boost airflow, experts
But dealing with existing buildings is a separate challenge,
noted Emmanuel of Glasgow Caledonian University.
“It’s not possible to build a new city, so it will have to
be retrofitted,” he said.
(Reporting by Sophie Hares; editing by Megan Rowling. Please
credit the Thomson Reuters Foundation, the charitable arm of
Thomson Reuters, that covers humanitarian news, climate change,
resilience, women's rights, trafficking and property rights.