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Print Edition> Nation
UPDATED: September 9, 2013 NO. 37 SEPTEMBER 12, 2013
Like a Furnace
The "urban heat island" effect has led to hotter cities than normal summer
By Yin Pumin
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SCORCHING: Tourists at the Bund in Shanghai on July 2 under 38 degrees Celsius temperature (XINHUA)

The summer has passed but its cruelty will perhaps always be remembered. It has been labeled as the hottest summer in China's history since nationwide records began in 1951, with nearly half of the country's population sweltering in a prolonged heat wave.

The nationwide average temperature stood at 22.3 degrees Celsius from the beginning of August, 1.3 degrees Celsius higher than the average level in previous years, said Chen Zhenlin, a spokesman for the China Meteorological Administration (CMA), on August 29.

"On August 6, the heat reached a peak, affecting more than 700 million people in 19 provinces and regions," said Wang Youmin, a researcher with the National Meteorological Center under the CMA.

In Shanghai, mercury in thermometers swelled to 40.6 degrees Celsius on July 27 and August 6, breaking a 140-year-old record and prompting local meteorological authorities to issue a code red temperature warning on those days. China uses a four-tier, color-coded weather warning system, with red being the most severe, followed by orange, yellow and blue.

Data from the National Meteorological Center also show, as of August 13, eight of the worst-affected provinces, including Zhejiang, Jiangsu and Jiangxi, had recorded an average maximum temperature of 35.6 degrees Celsius since July, with temperatures at 477 weather sites recording new records.

According to local government reports, at least 40 people died from heat-related health problems in south China this summer. In Shanghai, more than 10 people died from heat stroke.

"The hot days were mainly caused by the North Pacific Subtropical High being particularly strong," said Sun Leng, a senior engineer with the CMA's Climate Data Center. The North Pacific Subtropical High is a semi-permanent anticyclone, which means that it is an almost continuously high-pressure region that causes large-scale circulation of wind round it.

Sun added that the North Pacific Subtropical High is a particularly important factor in determining the summer climate in China.

But meteorological experts also admitted that human activities have also contributed to the increase in temperature.

According to Zhou Fuduo, a professor at the College of Civil Engineering and Architecture of Zhejiang University, some of the summer discomfort experienced stemmed from the urban heat island (UHI) effect. The UHI effect is where a metropolitan area is significantly warmer than its surrounding rural areas due to human activities.

"We can see that those who died from heat stroke lived in cities," Zhou said.

Planning errors

The term UHI comes from the fact that in an air-temperature-distribution graph, the high-temperature part has a shape of an "island."

Starting in the early 19th century, studies of these "heat islands" focus on the man-made effect of a temperature gap between a city's downtown and suburban areas and the resulting impacts on the urban ecological environment.

"There is a clear relationship between high temperatures and urban planning," said Yu Kongjian, Dean of Peking University's College of Architecture and Landscape Architecture.

In his opinion, air duct blockage, wetland degradation and loss, reduction of green spaces, enlargement of urban areas and the popular usage of glass curtain walls in constructing modern office complexes will all further worsen the UHI effect. He warned that even a small miscalculation or mistake in urban planning may lead to the destruction of the entire ecological system.

"In general, our city planners put a lot into the design of traditional infrastructure but don't spend enough time on infrastructure," Yu said, adding that this summer's heat waves were belated warnings against today's unsustainable city planning practices.

"Proper city planning requires the use of science, and scientific models and calculations tell us that you must leave enough space to be reserved as 'permanent non-construction areas' between different districts that can provide buffer zones for the city," Zhou said.

He complained that these buffer zones, including farms, wetlands and green areas, which should have been kept in larger cities, are often misused for building business districts or residential areas. "The larger a city expands, the stronger its UHI effect is," he said.

Since the 1970s, Zhou has begun studying the UHI problem affecting Hangzhou, the capital city of Zhejiang. When he began his research, the temperature gap between the city's urban and suburban areas was just 2 to 3 degrees Celsius. But today, the gap has reached 7 to 8 degrees Celsius.

Except for meteorological factors, the changes in the city's population, energy consumption, transportation methods and building areas have contributed to the growing UHI effect, Zhou explained.

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