Sat, Jul 20, 2019 - Page 8 News List

Looking at greenery to fix extreme heat issues

By Wang Pin-hui 王品惠

Europe was hit by an exceptional heat wave last month. On June 28, the temperature in Gallargues-le-Montueux in southern France reached a record 45.9°C.

According to a report by the United Daily News, the heat wave was caused by hot air moving northward from the Sahara into western and central Europe. To cool down, people scrambled to buy fans and air-conditioning units, apart from playing with water.

Air-conditioning was not common in Europe before. Data from the International Energy Agency showed that while 90 percent of US households own air-conditioners, fewer than 5 percent of European homes have them since temperatures of above 32°C often lasted for no more than five days a year.

However, summer temperatures in Europe have been rising rapidly in the past few years, often lasting up to two weeks per month. An article in US News & World Report said that such a transition was forcing European homeowners, offices and health centers to consider investing in air-conditioning. This would affect European governments’ assessment of sustainability goals to become carbon neutral.

Taiwan has also been sweltering in high temperatures during summer in recent years. Is it also suffering from a heat wave? As an island nation, Taiwan rarely suffers from scorching temperatures of over 40°C. However, the urban heat island effect might have a bigger impact on Taiwanese cities than severe heat waves caused by climate change.

Vehicle exhaust, dense concrete buildings and asphalt roads cause increases in urban temperature. When people keep using air-conditioning, it releases waste heat into the atmosphere, making it even hotter outside and creating a vicious cycle of heat absorption.

Air quality has also deteriorated drastically. Ground-level ozone pollution caused by the interaction between the sun’s ultraviolet rays and artificial pollutants, such as nitrogen oxides and volatile organic compounds, are harmful to health and can trigger asthma, eye discomfort and respiratory problems.

The most effective method to alleviate the urban heat island effect is to expand a city’s green area by planting trees that can form a dense and complex canopy to provide shade and intercept particulate pollution. At present, the total area of greenery that covers the six special municipalities is less than 10 percent.

Reports have also said that the government has not paid much attention to the maintenance of street trees. Narrow tree wells and excessively compacted soil resulting from wrong planting management make it difficult for the roots of such trees to grow normally. If the canopy does not grow well because the roots are restricted, the trees would not be able to form an effective shade.

Another way is to create a wind ventilation corridor to enhance urban air mobility, and introduce cold and humid air from the river into an urban area. European cities such as Munich, Germany, began this practice in the 1970s.

As for Taiwan, buildings are increasingly being built near rivers for better views, blocking the entrance of wind corridors. Furthermore, the high complexity of wind field simulation and poor control of current urban design regulation for land development are also challenges for policymakers and urban planners.

In the face of the threats from extreme climate change and the urban heat island effect, the government should enhance the nation’s green infrastructure through planting design and management. Green areas, parks and rivers for wind corridors are also indispensable to purify the air and reduce the risks of high temperatures in every aspect.

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