Haze, waterlogging, high temperatures?? From winter to summer, our cities struggle exhausted through one predicament after another. "In fact, these surface 'symptoms' are all related. If we use mechanical engineering thinking to deal with them one by one in isolation, not only will we fail to solve the problem, we may even create a vicious cycle." Kongjian Yu, Dean of the College of Architecture and Landscape Architecture at Peking University, said: "The root of the problem lies in the overall loss of the city's ecological functions."

The urban system is ill; waterlogging and heat are just symptoms

　　The urban ecosystem is ill; high temperatures are merely a "symptom"

　　"The city's fever is only a symptom; the source of the illness is the overall loss of the city's ecological functions"

　　News viewpoint: This summer's sustained high temperatures have drawn attention to the urban "heat island." So to what extent can planning and layout affect a city's "temperature"?

　　Kongjian Yu: Urban planning affects temperature in two ways. At the micro level, there is the "heat island," which is directly related. The city's scale, pattern, and the uniformity of green space distribution all directly affect urban heat. For example, Tiananmen Square lacks green space and water surfaces, so its heat island effect is very obvious.

　　At the macro level, urban planning may also indirectly affect the global climate, because the quality of urban planning is related to urban energy consumption, that is, carbon emissions.

　　From the perspective of the city's overall functional layout, the scale of people's daily activity ranges directly determines the amount of carbon emissions. If the city is treated as a machine and divided into zones—housing here, commerce there—then people's daily travel must inevitably rely on large volumes of traffic and large numbers of cars. Greenhouse gases produced by vehicle exhaust directly affect the urban heat island and also indirectly affect larger climate change.

　　News viewpoint: Besides the heat island effect, vehicle exhaust is also a major cause of "haze."

　　Kongjian Yu: Yes, temperature is only one aspect. The "heat island," air, and water are in fact interrelated. A while ago everyone discussed haze, then urban waterlogging, and now temperature. This is like a person falling ill: "fever" is only a symptom. The source of the illness is not high temperature; it may be a problem with the kidneys, or with the respiratory system, or a lesion in the blood system. Likewise, haze is only a surface symptom. Where is the problem?

　　It lies in the overall loss of the city's ecological functions; the city has lost its own capacity for regulation.

　　The Olympic Park is among the largest in Asia, but it is not in a densely populated residential area.

　　News viewpoint: Are haze, waterlogging, and the increasingly severe "heat island" different symptoms of the same "urban patient"?

　　Kongjian Yu: Viewed systematically, Beijing's water shortage is also related to rising temperatures. Water has a high heat capacity, and evaporation can absorb a large amount of heat. Wetlands and forests could originally store water; but now, because of waterlogging problems, every year Beijing hopes to quickly drain rainwater after rainfall. On the other hand, Beijing's groundwater is being lost every year, dropping one to two meters a year. The decline in groundwater also leads to a decline in the regulatory capacity of the city's entire natural system.

　　Water systems, wetlands, forests, and farmland—these natural elements form a system that provides cities with various ecological "services," including "air conditioning." I call this natural system "ecological infrastructure." Its quality and pattern determine the quality of the urban environment and determine its capacity for self-regulation of urban temperature, atmosphere, and floods and droughts.

　　Our current "air conditioning" uses artificial technology to improve the small environment; it does not improve the larger environment and may even make it worse. But the ecological "air conditioning" system regulates temperature "for free."

　　News viewpoint: In recent years, people have paid increasing attention to environmental and ecological issues, and urban construction has been striving in this direction.

　　Kongjian Yu: Our urban construction has many achievements, but there are also many misconceptions.

　　Overall, Beijing has a large amount of greening, but the green space that residents actually come into direct contact with is not as much as imagined, and the pattern is incomplete. For example, Chaoyang Park and the Olympic Park are among the largest in Asia, but they are not in densely populated residential areas. Their accessibility for residents is not very good, and they do not provide better services for the daily activities and lives of more urban residents.

　　Beijing has a very good tradition of planting trees in courtyard houses, so although the old city is very dense, the streets are shady. For example, on Gulou West Street, the roads are lined with large locust trees. No matter how hot the weather is, when you walk under the trees, you are still within the range of human tolerance. First, the trees block sunlight; second, the transpiration of leaves absorbs a large amount of heat, creating a microclimate environment.

　　If the distribution of green space is unreasonable, greening cannot directly improve people's living environment. Ecological infrastructure must directly relate to people's daily activities. Green space should dissolve into the city, into streets, communities, and workplaces.

　　At the same time, the quality of green space itself also directly affects its benefits. You can observe that in recent years, including in Beijing, much of the greening in many cities has been about beautification: lawns, flower beds, small bridges and flowing water, Taihu stones?? But in fact, what plays the greatest role is trees and forests, which can draw up groundwater and transpire to lower temperatures while sheltering people. This is the most effective.