Sprawling cities are fast becoming unmanageable according to the “State of the World’s Cities” report of the United Nations Centre for Human Settlements completed in June 2000. It found that the existing institutions governing the administration of cities are not adequate to control the sprawling urban centres. The UNCHS defines a sustainable city as one that has a lasting supply of the natural resources on which its development depends and a lasting security from environmental hazards which may threaten development achievements.

In the United Kingdom the net change from rural to urban land use is in the region of 6,500 hectares per annum. Globally, agricultural land accounts for 38 percent of all land: this is the resource that is to ensure food production for the world’s population.

Biologically Productive Areas of the Planet

The Earth has a surface area of 51 billion hectares, of which 36,6 billion are ocean and inland waters and 14,4 billion are land. Only 9,1 billion hectares of land and 2,3 billion hectares of water provide economically useful concentrations or resources to be considered biologically productive. The remaining 39,6 billion hectares are marginally productive or unproductive for human use, as they are deep oceans, are covered by ice, or lack fertile soils and accessible water.

The pressure of the world’s 6.2 billion people is slowly turning productive land into desert on every continent. Desertification affects up to one-third of the Earth’s land area and impacts on more than 1 billion people in 110 countries.

The impacts are happening across the globe: in the Sistan basin shared by Afghanistan and Iran, dust and sand have buried more than 100 villages; in Kazakhstan half of its 25 million hectares of grain land has been abandoned; in China the 5 million hectare Bardanjilin Desert is slowly starting to merge with the 3 million hectare Tengry Desert; in Nigeria some 350,000 hectares of land are lost every year; whilst in Kenya over 80 percent of the land is vulnerable to desertification.

12.8.1 Trees

Trees and plants modify air cooling in summer and air warming in winter. They provide shade to buildings and landscape surfaces, thereby reducing the ‘heat sink’ effect. They stabilise ground conditions, preventing soil erosion. They absorb groundwater and slow the movement of rainwater across the ground surface. More specifically, they absorb CO² emissions from the air. It is estimated that 15 trees are required to convert the carbon emissions of a typical car over a year and about 40 trees for a house. An examination of the scale of conversion quickly illustrates why we have such a problem globally.

12.8.2 Soft Landscaping

Soft landscaping, like trees, performs a valuable function at many levels. It supports biodiversity, especially if it is indigenous planting. Grasses and shrubs are as effective at converting CO² as are trees. Soft landscaping has the added advantage of attenuating the movement of rainwater to minimise erosion. Using natural bio systems can make it possible to deal with many of the consequences of rainwater management without making it someone else’s problem.

12.8.3 Hard Landscaping

Hard landscaping has at least two negative environmental impacts; firstly, it collects and reflects heat, requiring additional cooling capability, and secondly, it speeds up the movement of rainwater, placing an additional burden on disposal systems and times.

Landscaping should rather attenuate climatic conditions: alternative materials and responses should be applied if heat build-up is problematic, whilst absorbent materials will slow down the rate of disposal whilst allowing ground water replenishment. There are many other design devices that can be used, such as retention ponds, to assist in this matter.

12.8.4 Brownfield Development

Development on Brownfield sites presents a number of positive advantages to a developer: it saves the cost of installing bulk services, it will be well-served by transport networks, it will be accessible for workers and users, the urban quality of the adjoining area is established (no rude surprises later, and more often than not, local authorities will offer handsome financial incentives for the rehabilitation of such sites.

Architects must however take particular care in investigating what remedial actions are required. Depending upon the previous use(s) of the site, remedial work may involve major work to remove polluted soils, for example. A thorough inspection of the site together with an in-depth investigation of the previous land uses will be the minimum requirement to reaching a fuller understanding of what may lurk below the surface.

12.8.7 Stormwater

The uncontrolled – and sometimes even the controlled – management of stormwater can result in the devastation of a very large area. In urban areas, the propensity of large hard surfaces causes stormwater volumes to become enormous and unmanageable very quickly. Collecting all the surface run-off and discharging it through one pipe will create eventual havoc at the final point of disposal. Every effort must be made to absorb as much rainwater on the site as possible so that the collective responsibility for dispersal is shared.

Secondly, simple discharge carries the risk of single-point pollution discharge as well. Any chemical spillage will, in terms of the former strategy, result in maximum impact at the final point of disposal. Dealing with such risks by elimination in the first instance, proper management in the second, and several points of control, third, will reduce the impact of spillage and resultant pollution enormously.

Sourced from:

An Architect's Guide to Designing for Sustainability
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