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The rapid urbanization that is taking place goes together with a rapid increase in urban poverty and urban food insecurity. By 2020 the developing countries of Africa, Asia, and Latin America will be home to some 75% of all urban dwellers, and to eight of the anticipated nine mega-cities with populations in excess of 20 million. It is expected that by 2020, 85% of the poor in Latin America, and about 40-45% of the poor in Africa and Asia will be concentrated in towns and cities.
Most cities in developing countries have great difficulties to cope with this development and are unable to create sufficient formal employment opportunities for the poor. They also have increasing problems with the disposal of urban wastes and waste water and maintaining air and river water quality.

Urban agriculture provides a complementary strategy to reduce urban poverty and food insecurity and enhance urban environmental management. Urban agriculture plays an important role in enhancing urban food security since the costs of supplying and distributing food to urban areas based on rural production and imports continue to increase, and do not satisfy the demand, especially of the poorer sectors of the population. Next to food security, urban agriculture contributes to local economic development, poverty alleviation and social inclusion of the urban poor and women in particular, as well as to the greening of the city and the productive reuse of urban wastes (see below for further explanations and examples).

The importance of urban agriculture is increasingly being recognised by international organisations like UNCED (Agenda 21), UNCHS (Habitat), FAO (World Food and Agriculture Organisation), and CGIAR (international agricultural research centres).

1. Food security and nutrition

The contribution of urban agriculture to food security and healthy nutrition is probably its most important asset. Food production in the city is in many cases a response of the urban poor to inadequate, unreliable and irregular access to food, and the lack of purchasing power.
Most cities in developing countries are not able to generate sufficient (formal or informal) income opportunities for the rapidly growing population. The World Bank (2000) estimates that approximately 50% of the poor live in urban areas (25% in 1988). In urban settings, lack of income translates more directly into lack of food than in a rural setting (cash is needed). The costs of supplying and distributing food from rural areas to the urban areas or to import food for the cities are rising continuously, and it is expected that urban food insecurity will increase (Argenti 2000).
Food prices in Harare, for example, rose 534 percent between 1991 and 1992 due to the removal of subsidies and price controls, spurring poor urban consumers to get access to food outside of market channels through home production or bartering (Tevera 1996).
Urban agriculture may improve both food intake (improved access to a cheap source of proteins) and the quality of the food may improve (poor urban families involved in farming eat more fresh vegetables than other families in the same income category).

In Harare, sixty percent of food consumed by low-income groups was self-produced (Bowyer-Bower and Drakakis-Smith, 1996).
In Kampala, children aged five years or less in low-income farming households were found to be significantly better-off nutritionally (less stunted) than counterparts in non-farming households (Maxwell, Levin and Csete 1998). Urban producers obtained 40 to 60 percent or more of their household food needs from their own urban garden (Maxwell and Zziwa 1992).
In Cagayan de Oro, urban farmers generally eat more vegetables than non-urban farmers of the same wealth class, and also more than consumers from a higher wealth class (who consume more meat) (Potutan et al.1999).

In addition to production for their own consumption needs, large amounts of food are produced for other categories of the population. It is estimated (UNDP 1996; FAO 1999) that 200 million urban residents provide food for the market and 800 million urban dwellers are actively engaged in urban agriculture in one way or another.
These urban farmers produce substantial amounts of food for urban consumers. A global estimate (data 1993) is that 15-20% of the world’s food is produced in urban areas (Margaret Armar-Klemesu 2000).
Research on specific cities and products yield data like the following:

• in Hanoi, 80% of fresh vegetables, 50% of pork, poultry and fresh water fish, as well as 40% of eggs, originate from urban and peri-urban areas (Nguyen Tien Dinh, 2000);
• in the urban and peri-urban area of Shanghai, 60% of the city's vegetables, 100% of the milk, 90% of the eggs, and 50% of the pork and poultry meat is produced (Cai Yi-Zhang and Zhang Zhangen in Bakker et al. 2000);
• in Java, home gardens provide for 18% of caloric consumption and 14% of proteins of the urban population (Ning Purnomohadi 2000);
• Dakar produces 60% of the national vegetable consumption whilst urban poultry production amounts to 65% of the national demand (Mbaye and Moustier 1999). Sixty percent of the milk consumed in Dakar is produced in/around the city; and
• in Accra, 90% of the city’s fresh vegetable consumption is from production within the city (Cencosad 1994).
• Over 26000 popular gardens cover 2438,7 hectares in Havana and produce 25000 tons of food each year; a total of 299 square kilometres of urban agriculture produces 113525 tons/year (Mario Gonzalvez Novo and Catherine Murphy in Bakker et al. 2000);

Urban agriculture to a large extent complements rural agriculture and increases the efficiency of the national food system in that it (IDRC 1998) provides products that rural agriculture cannot supply easily (e.g. perishable products, products that require rapid delivery upon harvest), that can substitute for food imports and can release rural lands for export production of commodities.

2. Economic impacts

Growing your own food saves household expenditures on food; poor people in poor countries generally spend a substantial part of their income (50 – 70%) on food. Growing the relatively expensive vegetables therefore saves money as well as on bartering of produce. Selling produce (fresh or processed) brings in cash.

In Addis Abeba, above-normal profits are earned by even the smallest-scale backyard producers with very low capital (Staal 1997).

In Harare, savings accruing to small-scale urban farmers are equivalent to more than half a month’s salary (Sanyal, 1996

In Nairobi in the early 1990s, agriculture provided the highest self-employment earnings among small-scale enterprises and the third highest earnings in all of urban Kenya (House et al. 1993).

In Mexico City production of swine brings in 10-40% of household earnings, urban cowshed-based milk can supply up to 100% of household income and in sub and peri-urban areas maize production provides 10-30%, vegetable and legume production even up to 80% of the household income (Pablo Torres Lima, L.M.R. Sanchez, B.I.G. Uriza in Bakker et al. 2000)

Besides the economic benefits for the urban agricultural producers, urban agriculture stimulates the development of related micro-enterprises: the production of necessary agricultural inputs and the processing, packaging and marketing of outputs. The activities or services rendered by these enterprises may owe their existence in part or wholly to urban agriculture. Other services may also be rendered by independent families and groups (e.g. animal health services, bookkeeping, transportation).

Input production and delivery may include activities like the collection and composting of urban wastes, production of organic pesticides, fabrication of tools, delivery of water, buying and bringing of chemical fertilisers, etc.)

Transformation of foodstuffs may include the making of yoghurt from milk, or the frying of plantains or yams, chicken or eggs, etc. This might be done at the household level, to sell at the farm gate or in a local shop or market, and larger units to sell in supermarkets or even for export.

Special attention is needed for the strengthening of the linkages between the various types of enterprises in clusters or chains. The municipality and sectoral organisations can play a crucial role in stimulating micro-enterprise development related to urban agriculture.
The video shows an example from Ecuador where the municipality has provided marketplaces for urban farmers. The organic refuse left after a market day is collected by a women's group who compost the refuse to use in their own farms. A true win-win situation. A similar example is shown from Dar es Salaam.

3. Social impacts

Urban agriculture may function as an important strategy for poverty alleviation and social integration. We mentioned earlier the positive stimulus it may give to women.

Several examples exist of municipalities or NGOs that have initiated urban agriculture projects that involve disadvantaged groups such as orphans, disabled people, women, recent immigrants without jobs, or elderly people, with the aim to integrate them more strongly into the urban network and to provide them with a decent livelihood. The participants in the project may feel enriched by the possibility of working constructively, building their community, working together and in addition producing food and other products for consumption and for sale.

In more developed cities, urban agriculture may be undertaken for the physical and/or psychological relaxation it provides, rather than for food production per se. Also, urban and peri-urban farms may take on an important role in providing recreational opportunities for citizens (recreational routes, food buying and meals on the farm, visiting facilities) or having educational functions (bringing youth in contact with animals, teaching about ecology, etc.).

4. Contributions to urban ecology

Urban agriculture is part of the urban ecological system and can play an important role in the urban environmental management system.
Firstly, a growing city will produce more and more wastewater and organic wastes. For most cities the disposal of wastes has become a serious problem. Urban agriculture can help to solve such problems by turning urban wastes into a productive resource.

In many cities, local or municipal initiatives exist to collect household waste and organic refuse from vegetable markets and agro-industries in order to produce compost or animal feed, but one can also find urban farmers who use fresh organic waste (which may cause environmental and health problems).
Quality compost is an important input that can fetch a good price, as the example from Tanzania shows. Compost allows an urban farmer to use less chemical fertilisers and by doing so preventing problems related to the contamination of groundwater. In addition, compost-making initiatives create employment and provide income for the urban poor.

Farmers may use wastewater for irrigating their farms when they lack access to other sources of water or because of its high price. The use of fresh (untreated) wastewater has the additional advantage for poor urban farmers that it contains a lot of nutrients (although often not in the proportions required by their soils and crops). However, without proper guidance, the use of wastewater may lead to health and environmental problems. Farmers need to be trained in self- protection during handling of the wastewater, proper crop selection and adequate irrigation methods, among other things.

Technologies such as hydroponics or organoponics, drip irrigation, zero tillage etc. substantially reduce water needs and health risks and are very interesting for the urban environment and can indeed be found in many cities.

The treatment and reuse of more urban wastewater in agriculture also needs to be ensured. This necessitates special decentralised treatment facilities and low cost (preferably bio-) technologies. In many cases, partial treatment will be optimal for agricultural reuse. More and more experience is being gained in public-private initiatives involving private enterprises and/or civic organisations in the development and management of municipal wastewater treatment plants. However, in most municipalities, the treatment capacity will be far lower than what is needed for many years to come, and farmers will continue to use raw wastewater - a fact that should urge municipalities and other actors to take proper accompanying measures.

Without a doubt, each situation will require a tailor-made solution, preferably to be found by involving the stakeholders in a process of participatory problem analysis, planning and implementation.

Secondly, urban agriculture may also positively impact upon the greening and cleaning of the city by turning derelict open spaces into green zones and maintaining buffer and reserve zones free of housing, with positive impacts on the micro-climate (shade, temperature, sequestration of CO2).
Degraded open spaces and vacant land are often used as informal waste dumpsites and are a source of crime and health problems. When such zones are turned into productive green spaces, not only an unhealthy situation is cleared, but also the neighbours will passively or actively enjoy the green area. Such activities may also enhance community self-esteem in the neighbourhood and stimulate other actions for improving the community's livelihood.

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