Big cities are becoming like "steamers" because of the urban heat island effect, and at the same time, extreme high temperatures are superimposed.
This summer, the high temperature in the Sichuan Basin exceeded 40 degrees. This high temperature lasted for a long time and has not subsided. The opening of primary and secondary schools has been repeatedly postponed, and many colleges and universities have also temporarily switched to online teaching models.
The slogans displayed in shopping malls say "42 degrees, slightly hot", but the situation behind them is that citizens and merchants have been told to save electricity.
Under such high temperatures, most of the early warning systems we rely on are forecasts 24 hours in advance, or short-term forecasts three days in advance. The accuracy of mid- and long-term warnings is really far from enough. This has led to the emergence of passive response situations such as "closing classes at the beginning of school" and "cross-regional power support".
What deserves more attention is that the health risks brought by high temperature are often ignored by everyone.
When the number of people living in cities exceeds 900 million, how cities should systematically respond to high temperatures has become an unavoidable issue.
Why cities have become “high temperature islands”
Many people may have felt that in the same hot weather, the temperature felt in the city is often much higher than in the suburbs.
Behind this is urban heat island effect It's working.
There are numerous and dense high-rise buildings, vast areas of asphalt roads, and concrete buildings. They absorb a huge amount of solar radiation during the day, but cannot dissipate the heat at night, just like a huge heat storage body.
Liu Xiang, an expert who is involved in research on the health risks of high temperature and heat waves, said that in super-large cities such as Chongqing, with dense populations and dense buildings, high temperature heat waves and urban heat island phenomena make residents more likely to be exposed to dangerous situations.
According to data from the International Labor Organization, among the 3.4 billion working population worldwide, the proportion of people exposed to high temperature environments was 65.5% in 2000, and has climbed to 70.9% in 2020.
This shows that high temperatures, which were originally a simple climate phenomenon, have evolved into current risks that pose a direct threat to our health.
Why are warnings so late?
At present, most of my country's high temperature warnings are still based on 3-day short-term forecasts, or 24-hour short-term forecasts.
This early warning mode is pretty good for dealing with one-time high-temperature weather. However, once it encounters a high-temperature heat wave that lasts for several weeks, it will be somewhat powerless.
The lack of mid- and long-term early warning and its lack of accuracy directly led to passive response.
For example, the school has just started the new semester, but has to stop teaching, or there is a situation that requires emergency deployment of power resources from other places, which has even triggered different opinions and debates about artificial rainfall.
During the period that started on June 1 and lasted until the end of August, more than 20% of counties and cities across the country experienced extreme high temperatures above 40 degrees. At the same time, the national average temperature also set a new height record for the same period since 1961.
If we are facing a new normal like this, if this early warning is still in a "temporary" state, it will be difficult to calmly deal with this situation.
A map to see where the risks are
So how should cities respond?
Dr. Ren Chao's team has come up with a very good idea with significant value, which is to start the work of producing a risk map covering high temperature and heat wave conditions.
The purpose of this map is to figure out where the high temperatures are most severe.
Ren Chao's team found that the risk area during the day is different from that at night.
During the day, groups such as those engaged in construction work outdoors, those delivering express items, and those responsible for environmental sanitation and cleaning are at the highest level of risk. If the disposal process is not timely and efficient, life-threatening situations may even occur.
Therefore, since May last year, Hong Kong has promulgated relevant regulations. For outdoor workers, every 45 minutes of working, they must replenish water and rest for 15 minutes.
When night comes, the risk is focused on the old communities, which are a collection of people living in them. The probability of air conditioning being widely used may not be high, and the heat and stuffiness are unbearable.
Send resources to where they are needed most
It’s not enough to have a map, you also have to know where help is available.
Ren Chao's team overlaid the risk map. The overlaid objects were existing community service points, summer resort centers, community living rooms and other facilities. Afterwards, they discovered an interesting problem, that is, there are two disaster relief points available in the richest area of Hong Kong. However, in the poorest district of Yau Tsim Mong, there is not a single related facility.
This kind of information is very valuable to decision makers.
By knowing where the shortages are greatest, we can appeal to the government, NGOs and businesses to deliver the drinking water, medicines and even temporary rest spots needed to combat high temperatures where they are most needed.
With its relatively complete social infrastructure and NGO organizations, Hong Kong is indeed in a leading position in Asia when it comes to dealing with extreme disasters such as high temperature and heat waves.
"Ventilation corridor" in urban planning
In the face of high temperatures, in addition to providing temporary relief, a more feasible long-term approach is to invest energy at the urban planning level and strive for progress.
Singaporean Khoo Teck Puat Hospital This is a very classic example.
When designing the hospital, three buildings were arranged in the shape of a letter "V". They faced the adjacent pond and looked like a large trumpet.
By introducing the cool sea and land breezes above the pond, the entire building complex can be kept cool even if the air conditioning is not turned on.
This design concept is like placing a "ventilation conveyor belt" in the city, which promotes heat from the ground to the air.
However, this idea is more suitable for the construction of new cities.
As far as the old city is concerned, its transformation is quite difficult and there is no possibility of large-scale demolition and reconstruction. However, it can be combined with the renewal of the old city to add greenery within a limited space, optimize the building layout, and gradually improve the microclimate.
When cities face high temperature conditions, they cannot just focus on the red warnings of those few days. What is more needed is a long-term mechanism that starts from the warning, goes through the rescue link, and ends at the planning stage.
First, create risk maps that meet accurate requirements. Then, resources must be accurately allocated to communities where they are most needed. Then, within the scope of urban design, passages for wind and water must be left open, and each step must be promoted in a practical manner.
Only by building the city into a resilient "sponge" that has the functions of absorbing water, dissipating heat, and protecting people can it be possible to add some calmness and reduce some expressions of helplessness in the face of increasingly intensified and more frequent high-temperature heat waves.
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