Human settlements and infrastructure

Much good agricultural land is threatened by chemical pollution, particularly - as here in China - by waste products from urban centres. Chemical degradation is responsible for 12 per cent of global soil degradation Source: UNEP, Zehng Zhong Su, China, Still Pictures

Urban areas occupy only 1 per cent of the Earth's land area (UNEP 2000). However, urban expansion, including land requirements for industry, transport and for leisure activities in all regions, increases pressures on land resources. In the United States, for example, about 400 000 ha of farmland are lost to urbanization annually and China lost about 5 million ha of farmland to towns and cities during 1987-92 (UNFPA 2001). Land degradation, river siltation and soil pollution, from acid rain and industrial wastes, are some of the environmental issues associated with urbanization and industrialization.

The waste generated by cities is a major source of degradation. It is estimated that about 1.95 million ha of land have been degraded by industry and urbanization (FAO 1996). One cause has been the export by some developed countries of hazardous and toxic wastes to developing regions.

The international response to this was the 1989 Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and their Disposal. The Basel Convention, which entered into force in 1992 (see Chapter 1), aims to reduce transboundary movements of hazardous wastes, minimize the creation of such wastes, and prohibit their shipment to countries lacking the capacity to dispose of hazardous wastes in an environmentally sound manner.

Urbanization has also spawned urban agriculture (see 'Urban areas'), which was hardly recognized internationally in the 1970s but has been expanding globally over the past 15-20 years, 'more rapidly than urban populations, and in many countries more rapidly than their economies' (Smit 1996). Urban agriculture takes place on both public and private land, both legally and illegally. More than 800 million urban dwellers were involved in urban agriculture in 1993 (Smit 1996). For example, in the Brazilian city of São Paulo, agriculture is a major planned land use in the city's metropolitan master plan, which was adopted in the 1990s.

In virtually all regions, urban agriculture has become one of the major food-producing activities. For example, most households in the Southeast Asia and Pacific Island sub-regions practise urban agriculture (Sommers and Smit 1994). About 30 per cent of the Russian Federation's food is produced on 3 per cent of the land in suburban dachas (Sommers and Smit 1994). In Moscow, families engaged in agriculture grew from 20 per cent of the city's population in 1970 to 65 per cent in 1990 (Smit 1996). During 1980-90, urban agriculture in the United States grew by 17 per cent (Smit 1996). In some African urban areas, the response by municipal authorities has been to cut down the crops to enforce land-use by-laws.

The impacts of urban agriculture include air, water and soil pollution, mainly from improper use of chemicals. Advocates of urban agriculture argue that, in addition to providing food, the activity can contribute to improving the environment through recycling organic matter. Solid wastes can be composted and used to fertilize soils.