So, what we need is a way
A group of scientists, in the
Proceedings of the National Academy of Sciences, report that they have
tested a few strategies to mitigate the rise of city temperatures and
perhaps at the same time turn down the rate of rise in greenhouse
temperatures as well.
Scientists argue that roofs, paved roads,
pipes, wiring, traffic, central heating and air conditioning, industry
and commerce and other such urban trappings could raise temperatures by
1°C to 2°C. It is also certain that cities are to expand and, thus, more
land areas are to be covered by roofs and roads.
If you go by analysis of urban growth
data, global urban area is expected to grow by 185% by 2030 and much of
that will be in China and India. In that same time Africa could see the
greatest proportional increase with its cities expanding by six-fold.
‘Urban expansion within these areas will
almost certainly be highly concentrated, exposing highly vulnerable
populations to land use-driven climate change,’ the authors of the
Adaptation strategies to
So the researchers started to think about
some simple changes that could reduce urban temperatures. The first
conclusion was that adaptations needed to be tailored to local climates
One simple answer is the ‘cool roof’ –
paint it white so it reflects the sunlight. This has been a proved idea
and in California’s Central Valley, at least, the temperature levels
fall. However, in other simulated environments, the measure didn’t work
well as reflective roofs lowered the temperature in winter necessitating
extra investment in heating fuels.
‘Green roofs,’ covered with turf or
planted with transpiring foliage, were more effective in other urban
climates. These highly transpiring structures did not compromise
summertime energy savings by demanding additional energy in winter.
The scientists suggest that cities need to
develop tailored strategies based on their local climatic condition and
needs. With judicious planning and careful choice of design, it could be
possible not only to counteract urban growth temperature increases but
even offset the effect of greenhouse gas warming as well, not just over
the cities, but beyond the cities as well.
The study delivered unexpected results. In
Florida, the team’s simulations significantly reduced rainfall, a result
that would have implications for water supply and local ecosystems.
There was no simple, one-size-fits-all
answer. Geography played an important role in any such calculations.
‘For Florida, cool roofs may
not be the optimal way to battle the urban heat island because of these
unintended consequences,’ said Georgescu as quoted by Tim Radford in a
Climate News Network release.
‘We simply wanted to get all these
technologies on a level playing field and draw out the issues associated
with each one, across place and across time,’ Georgescu added.
(With Inputs from Tim Radford's Report released by
Climate News Network)