The global population is expected to grow to 8.9 billion in 2050 as predicted; more than 60 percent of people will live in the city in the year of 2025 worldwide, and in 2050 this number will increase to 70 percent (Cohen, 2003). As the rapid development of urbanization and population growth, the urban area will inevitably expand to gain more construction land from nature. It can be predicted that in the future the problems such as urban heat island effect, ashes effect, water population, and eutrophication will be more serious than today’s situation. Thus, it is important to develop and modify urban ecological infrastructure.
Traditional city is usually assembled by ‘grey infrastructure’ (figure 1). Grey infrastructures refer to structures and buildings such as hospital facilities, water supply systems, storm water systems and commercial buildings; and so far, modern structures are made of concrete which presents the color of grey. These grey infrastructures provide the basis of the normal function of a city.
However, the grey infrastructure has an apparent flaw which is single functional designed. To us, our infrastructures have many functions; but, they have on function to the ecosystem. For example, the design of river channel is often for flood protection; indeed, the river channel should also have other functions such as maintaining biodiversity to the ecosystem. The problems such as urban flood with high frequency and traffic congestion reveal that grey infrastructures not only cannot solve the complicated issues a city faces but also would bring ecological issues.
In the mid-1980s, the concept green infrastructure is put forward to solve urban issues by constructing with nature (Wikipedia). Green infrastructure is a green network system consisting of parks, forests, wetlands, conservative areas, green belts and other ecological corridors within the city. It plays a significant role in urban flood control, rainwater regulation and local climate regulation. A study shows that green infrastructure, i.e. the green space network, is important in dealing with climate change and improving surface runoff of rainwater (Gill, Handley, Ennos, & Pauleit, 2007). Also, Margaret Bryant finds ecological greenways and parks can play a critical role in biodiversity in urban areas (Bryant, 2006).
Green infrastructure is not single functional design; it can bring multiple benefits. For instants, green roof can effectively reduce the room temperature by 3°C-6°C, not only reducing the urban heat island effect, diminishing electricity consumption, but also has many ecological benefits such as water storage and emission reduction, purification of roof runoff pollution, and beautification of the environment (Getter & Rowe, 2006).
Figure 2 Green roof
Thus, it is important to integrate grey infrastructure and green infrastructure to provide collaborative ecological infrastructure. By optimizing grey infrastructure through green infrastructure and the concept of multi-function design, a better maintenance of integrity and vitality of urban ecosystem service can be acquired. Moreover, the infrastructure system which is the combination of grey and green infrastructure can interconnect urban artificial system and natural system; and a more integrated, stable and sustainable urban infrastructure system can be formed.
Urban infrastructure can be divided into four parts: wetland, green land, structure and contaminate and waste exits.
Wetland includes rivers, lakes, reservoirs, ponds and other wetlands. In some urban area, the river is designed to provide flood protection, satisfy water consumption or just for aesthetic needs. But, a river in nature has more functions: regulating runoff, degrading pollution, purifying water quality, and maintaining biodiversity. Also, in some parks, the ponds or reservoirs exist without a connection. If these ponds and reservoirs can be connected, the storage capacity of water will increase through water flow. Besides, good connectivity can bring fresh water and material to facilitate aquatic organism survival and reproduction.
Green land which is also known as the lung of the city includes urban forests, grass land, green corridors, green gardens, and parks. Although in many cities, the quantity of green land is large, but the quality is lower than expected. Grassland is a typical example; most cities build lots of grass lands for the citizens, but the grass lands only provide green space for leisure time and nothing else. Some grass lands only have extremely limited water storage capacity, under heavy rain situation, these grass lands can hardly help to absorb excessive rainwater. In fact, grass land can be a good place for water storage capacity, water purification and local climate regulation, not just a place for people’s leisure time. It also can be transformed from landscape green land to functional green land by connecting to green land.
Figure 3 flood in the urban area
The structure includes buildings, pavement, road, riverbed, and embankment, etc. To human beings, a building may be multi-functional just like a shopping mall providing shopping service to entertainment service, even education service. However, to the ecosystem, the building just a useless concrete box. The impermeable surface of building blocks gas and water exchange between air and land. Also, the hardened road surfaces, ditches, and embankment are made of impermeable and dark color materials. These surfaces significantly absorb more solar radiation which causes the break of material and energy balance in the urban area. The intuitive manifestation of this consequence is urban heat island effect (figure 4 & 5). Mitigation of urban heat island effect can be accomplished by designing the green roof and changing the material of surface to reduce the absorption of solar radiation. Moreover, the impermeable surfaces limit the discharge of rainwater; especially in stormy days, lots of rainwater is accumulated within the urban area and cannot be discharged (figure 3). So, the multi-functional road is necessary, it not only satisfies the traffic demand but also can facilitate water and gas exchange between air and earth which is under the road.
Figure 4 Urban heat island effect
For contaminant and waste, traditional sewage system transports all contaminant and waste to the suburbs. People build garbage storage site to pile up the pollutants. But, the accumulation of garbage beyond the carrying capacity of suburbs. The waste disposal by landfill merely wipes the scene of garbage out from people’s horizon. What we need is a system which contains the function of storage, purification, treatment, and recycling.
A city is a complex and comprehensive ecological system. Under the pressure of increasing population, limited resource and climate change, single function infrastructure cannot help us to deal with these issues. In the ecosystem, no one exists with single function; for instant, a river is not just a channel with flowing water, it can provide fresh water to lives, help us to transport cargo and conduct energy exchange. Our tradition infrastructures only have one function which is to satisfy our need. They can do nothing except providing room for our activity. But, they are useless to the rest of world. In fact, we need multi-functional infrastructure; it can not only support our activity but also can provide ecological services to the ecosystem.
Bryant, M. M. (2006). Urban landscape conservation and the role of ecological greenway at local and metropolitan scales. Landscape and Urban Planning, 76, 23-44.
Cohen, J. E. (2003). Human population: The next half century. Science, 302(5648), 1172-1175.
Getter, K. L., & Rowe, D. B. (2006). The role of green roofs in sustainable development. HortScience, 41, 1276-1286.
Gill, S. E., Handley, J. F., Ennos, A. R., & Pauleit, S. (2007). Adapting cities for climate change: the role of the green infrastructure. Built Environment, 33, 115-133.
Wikipedia. Green infrastructure. Retrieved from https://en.wikipedia.org/wiki/Green_infrastructure