This summer brought unprecedented extreme weather to Beijing.
The worst storm in 20 years hit the capital on July 10. A dust
whirlwind, the most severe of its kind seen in 55 years, devastated
the construction site for the National Swimming Center on August
27. It left 44 workers injured and two dead. In addition, many
other short-lived storms have also visited the capital this
summer.
According to the meteorologists, there is a connection between
the extreme weather and city planning considerations. This summer's
extreme weather has been notable for four characteristics. All
represent unprecedented phenomena:
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When extreme weather came, it did not last long. The storm of July
10 lasted less than 3 hours. The whirlwind on August 27 was over in
20 minutes.
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It would come and leave, both suddenly and unexpectedly. Its
unpredictability made it impossible for people to take steps to
prepare for it.
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The extreme effects have been localized. Beijing has a built-up
area of some 1,600 square kilometers, but the storm of July 10
focused itself on an area of less than 100 square kilometers. Some
100mm of rain fell in the northwest while the rain barely made the
ground wet in the south of city. On August 27, the whirlwind only
affected an area of several hundred square meters.
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The weather has brought unprecedented losses and disruption. The
freak whirlwind brought death and injury to the city on August 27.
The storm of July 10 only lasted three hours but it brought the
capital to a standstill with a serious traffic jam.
Although the extreme weather is the result of quite a number of
different factors such as cold air and convection currents, city
planning and construction do exert an important influence on the
local weather.
Meteorological observations reveal that heavy storms and high
winds are closely related to the city's "micro-climate". Large
areas of concrete or asphalt road surface produce localized "heat
islands" within the urban environment. This summer, temperatures of
some 80 Celsius were being recorded on concrete and asphalt road
surfaces. Meanwhile neighboring areas of greenery were only about
40 Celsius.
Such large temperature variations in close proximity make
localized extreme weather conditions more likely. Meteorologists
have pointed out that when the temperature of concrete and asphalt
roads reaches 80 Celsius, it can have a significant impact on
rainfall. This is why Beijing residents could find flooding to one
side of a road but just a little rain on the other.
In addition, there is what is known as the "valley effect". This
is becoming an increasingly apparent feature of Beijing's
townscape. When the city as a whole encounters winds of say force 6
or 7, they are concentrated in the "valleys" between high
buildings. Here the wind can briefly touch force 12. This is
Typhoon level! It is hardly surprising that so many billboards have
been blown down this summer.
Meteorologists suggest that greater consideration should be
given to avoiding localized extreme weather during the planning
phase. It would be helpful to increase large-scale tree-planting
and grassed areas and reduce the area of road surface. High
buildings should be carefully laid out in relation to each other
and built further apart. City planning should allow for the
provision of "urban wind paths" to proactively control how the wind
will move through a built-up area. Not only can these improve air
quality by quickly removing pollutants, but they can also benefit
the urban "micro-climate" reducing the chances of extreme
weather.
(China.org.cn by Wang Qian, September 5, 2004)