Urban ecological footprints in Africa
Africa’s rate of urbanization is the highest in the world. This is relevant to ecologists working in Africa because urban growth is strongly associated with habitat destruction, and also creates new fields of study. The ecological footprint concept is used to illustrate how urban settlements in Africa impact on rural ecosystems. At an aggregate level, African countries have the lowest ecological footprints in the world. However, there is little available data for individual cities, so evidence is fragmented making concerted policy initiatives difficult. Wood fuel continues to be a major source of energy for urban households and there is a long running debate as to what extent providing wood fuel for urban use damages forest ecosystems. Growing evidence contests the assertion that urban wood fuel markets are responsible for forest degradation. Although there are other options available, the social consequences of switching energy sources need to be taken into account. Outright bans, for example on charcoal, would lead to a loss of livelihoods in rural and urban households, and may not solve deforestation as well as increasing fossil fuel use would increase the ecological footprint.
Le taux d’urbanisation de l’Afrique est le plus élevé du monde. Cela concerne les écologistes qui travaillent sur ce continent parce que la croissance urbaine est étroitement liée à la destruction des habitats, et cela ouvre aussi de nouveaux champs d’étude. Le concept d’empreinte écologique est utilisé pour illustrer comment les installations urbaines en Afrique ont un impact sur les écosystèmes ruraux. Pris tous ensemble, ce sont les pays africains qui ont la plus légère empreinte écologique du monde. Cependant, nous disposons de peu de données pour des villes individuelles, de sorte que les renseignements sont fragmentés et qu’il est difficile de prendre des initiatives politiques concertées. Le bois de feu continue àêtre une des principales sources d’énergie pour les ménages urbains, et il existe un débat de longue haleine quant à savoir dans quelle mesure l’approvisionnement en bois pour la consommation urbaine endommage les écosystèmes forestiers. Des preuves de plus en plus évidentes remettent en question l’assertion selon laquelle les marchés urbains de bois de feu seraient responsables de la dégradation des forêts. Bien qu’il y ait d’autres options possibles, il faut prendre en compte les conséquences sociales du passage à d’autres sources d’énergie. Les interdictions totales, par exemple du charbon de bois, entraîneraient la perte des moyens de subsistance de ménages ruraux et urbains, et pourraient ne pas résoudre le problème de déforestation, tout comme l’utilisation accrue des combustibles fossiles augmenterait l’empreinte écologique.
The United Nations Population Fund’s ‘State of the World Population Report’ for 2007 contains some statistics that are a cause for ecological interest. In Africa at the turn of the last century in 1900, only 5% of the population lived in urban areas, while in 1960 the figure was about 20% and today it is estimated to be about 38%. The urban population of Africa is expected to double between the years 2000 and 2030 (from 294 million to 724 million). Africa’s current annual urban growth is the highest in the world, at more than 4% (UN Population Fund, 2007). If the increase in urban dwellers means a decrease in rural dwellers, this will please those ecologists who consider people ‘chiefly as agents of disturbance’ (Mcintyre, Knowles-Yaňez & Hope, 2000: 6) while those ecologists who work in peri-urban areas may be more alert to the impacts that an encroaching built environment brings. However, there is a third group of ecologists who will see the urban environment itself as presenting interesting subjects of study. This article will demonstrate that African urbanization has something of relevance for all the three groups.
There is no denying the effects that urban areas have on habitats, the environmental impacts of which are felt within the built environment, in the immediate hinterland, in neighbouring regions and globally. Impacts of human activities stem from the use of the natural environment both as a resource to provide goods and services and as a repository for waste. Use of land and water causes changes in natural habitats and disrupts existing eco-systems. Unsustainable use of groundwater causes the water table to drop and can lead to land degradation. In Africa, the source of urban water supply has been shifting from groundwater supplies to rivers (Showers, 2002). Using rivers affects both upstream habitats by disrupting local hydrological cycles and downstream habitats because of changes in water flows, which affect fish stocks and biodiversity. Moreover, discharge of untreated sewage causes eutrophication and together with industrial chemicals, damages aquatic ecosystems. Coastal habitats are particularly vulnerable to urban development where activities include dredging shipping channels and harbours (McGranahan, Satterthwaite & Tacoli, 2004). Land is lost as a habitat because it is built on and also because materials for building and other industrial activities are mined. Soil is polluted as a result of unregulated dumping of urban waste, which then decomposes and can pollute water sources. On the positive side of urbanization, peri-urban areas can be set aside as protected natural or green areas, which support biological diversity, sometimes at levels higher than in the surrounding rural areas (Anon, 2006).
Urban areas not only contribute to the destruction of rural habitats but also to the creation of new ones in both urban and rural areas thereby providing interesting new phenomena for study. These new habitats can have serious consequences for human health, for example by becoming breeding grounds for carriers of vector-borne diseases. Polluted water sources, such as soakaway pits and septic tanks with high amounts of organic matter, have been identified as breeding grounds for Aedes aegypti, the mosquito vector of dengue and urban yellow fever (McGranahan et al., 2004). The anopheles mosquito, the malaria vector, also thrives in surface water resulting from inadequate drainage systems. Urban agriculture can be an important Anopheles breeding site, for example in rice paddies (Matthys et al., 2006). Yet, despite its clear economic and social importance, this aspect of the urban eco-system in Africa appears to be a much under-researched field and there are many interesting scientific questions requiring answers (Robert et al., 2003). For example, why are the transmission rates for malaria so much lower in urban areas than in rural areas? Why are the transmission rates between cities, and within districts in the same city, different? In 2006, the Malaria Journal appealed to ecologists to use their skills in relation to vector management for malaria control because the type of ecological skills needed ‘are very scarce and rarely applied in Africa today’ (Mukabana et al., 2006).
Returning to urban–rural interactions, what is unsettling from an ecological perspective is the scale and location where urban growth is taking place rather than the rate of urban growth. The doom scenarios of a few years ago that predicted the rise of mega-cities (defined as cities with more than 10 million inhabitants) have not materialized (Tannerfeldt & Ljung, 2006). Smaller cities, defined as those with a population of <500,000 (United Nations, 2006) appear to be the trend for the short- to medium-term future. However, there is no agreed lower limit of what constitutes a ‘small city’ as classification of ‘urban’ varies between countries. In a review of 63 papers related to urban ecology, Mcintyre et al. (2000) found that there was an assumed common understanding of the term but that it lacked hard definition. Not withstanding these problems, small cities are already considered to be home for more than half of the world’s urban population and they are expected to account for about half of urban population growth between 2005 and 2015. Living in small cities has disadvantages because they tend to have poorer quality services and are hence more vulnerable eco-systems than large cities. Planning and regulatory systems are often rudimentary. Small cities do not receive the government investments and attention that large cities can command, and they are unable to achieve comparable economies of scale in service provision, land use, transport and water and energy provision. The wealth of a city is also a significant factor for inducing habitat changes in rural areas, for example, demand for meat and grains can lead to rural agricultural systems dominated by monocultures.
What is driving urbanization and can it be controlled? Not surprisingly, natural population growth is the main cause. The other two main factors in urbanization are bureaucratic actions (reclassification by planners of rural and urban areas) and rural migration (which is influenced by drought, famine, ethnic tensions, civil strife and war). Trying to stop urbanization is, to all intents and purposes, impossible (Tannerfeldt & Ljung, 2006). The challenge is to make urban life sustainable. No matter where we live, food, energy, water and the other basic amenities for life must be produced and wastes disposed of. If goods and services are to be provided sustainably then this must be within the limits of the natural resources available and the ecosystem’s capacity to respond.
This article reviews the environmental impact of urban areas in Africa both in terms of their ecological footprint and the effect on the human environment. Although there is some scepticism about the methodology (Moffatt, 2000; Opschoor, 2000), ecological footprints are a useful tool for highlighting the environmental impacts of urban systems based on resource consumption. There is a particular focus on energy production and use as this is one of the key parameters used to construct the concept of the ecological footprint. Although all energy sources are derived from natural resources, this article concentrates on renewable sources of biomass and water because these are extracted from the biosphere throughout Africa whereas nonrenewable energy resources, such as coal and oil, are more limited in extraction. Reference is also made to other environmental problems, such as lack of sanitation, which pollute soil and water. Some suggestions are made about how to reduce the urban ecological footprint of African cities.
The ecological footprint of urban areas
Cities now account for a large and growing proportion of the demand on natural resources both as a source of services and as a repository for waste. Some analyses suggest that urban areas account for 80% of carbon emissions, 75% of all wood use and 60% of freshwater withdrawn for human uses (including water for irrigated crops consumed by urban dwellers) (O’Meara, 1999). One means of assessing the impact of human activity on the use of natural resources is the concept of the ecological footprint. Using a common set of indicators (although there is no consensus on which indicators to use and how to measure them) for a defined entity such as an individual, a city or a country, it is possible to make a cross comparison of ecological footprints. For example, as a measure of the ecological footprint of countries, the World Wildlife Fund (WWF) compares renewable natural resource consumption with nature’s biological productive capacity. This footprint is expressed in global hectares based on world-average biological productivity. Productive land includes all the cropland, grazing land, forest and fishing grounds required to produce the food, fibre, wood fuel and timber a country consumes, to absorb the wastes emitted in generating the energy it uses, and to provide space for its infrastructure (including the area covered by hydropower) (WWF, 2006). WWF estimated that for Africa in 2003, the ecological footprint was 1.1 global ha per person, somewhat lower than the World footprint at 2.23 global ha per person and high-income countries at 6.4 global ha per person (WWF, 2006: p28). However, this is no reason to be complacent about Africa as aggregated data often disguise local problems and there appears to be little specific data about the ecological footprint of Africa’s cities.
The World Wildlife Fund’s measure of a country’s ecological footprint includes a measure of its energy footprint because energy is considered to be one of the most significant demands that both draw on the biosphere as a resource and as a sink to absorb waste products from energy use. The energy footprint of a country represents the area required to sustain its energy consumption. It encompasses four types of energy: fossil fuels (coal, oil and natural gas), biomass (fuel wood and charcoal), nuclear and hydropower. An assessment of the energy footprint estimates the land required for sequestering the excess CO2 from burning fossil fuel, or to replace it with biomass, for harvesting fuel wood, and for nuclear energy and hydropower (WWF, 2002). Biomass is the main source of energy in Africa. In 2001, 59% of energy consumption was from biomass (UN-DESA, 2004) primarily in the form of wood fuels (fuel wood or charcoal). The main end-use of roundwood production in Africa is as an energy resource [88% of 546 million m3 in 2005 (FAO, 2006)]. What are the ecological consequences of urban wood use in African cities? The production of wood fuels is often linked to clearing of forests that leads to loss of indigenous biodiversity, destruction of vital ecosystems and habitats (see for example, Kirubi, Wamicha & Laichena, 2000). In 1995, FAO estimated that the annual deforestation rate in Southern Africa ranged between 0.75% and 2.2% (FAO, 2000). The link between wood fuel use and deforestation has its origins in the 1970s when an extensive literature claimed that wood fuel demand was outpacing sustainable supply (e.g. Ekholm, 1975). From these claims, a widespread assumption gained ground that by the end of the century much of Africa would have been deforested to provide fuel wood for the poor (Nash & Luttrell, 2006). However, the disaster scenarios (at least at the aggregate level) have proved to be unfounded. Later research has shown that not all deforestation can be blamed on wood fuel cutters and charcoal producers. Leach and Mearns in their classic study Beyond the Woodfuel Crisis suggested that if all wood fuel use stopped tomorrow, deforestation rates would hardly be altered (Leach & Mearns, 1988). There is a growing body of research in Africa, which supports the hypothesis of Leach and Mearns (see for example, Chidumayo, 1993; Arnold et al., 2003; Nash & Luttrell, 2006) and bans are considered counterproductive (Girard, 2002). However, the subject is controversial and there continue to be calls for halting charcoal production based on its negative ecological consequences.
The sources of wood fuels are more diversified than was thought in the 1970s and sources are context specific (Girard, 2002). For example, there are a number of ‘free’ sources of wood that urban households can draw on, such as timber yards, discarded packaging and peri-urban wood lots in the urban hinterland (Leach & Mearns, 1988; Hosier & Kipondya, 1993). There are little data on these sources (indeed, there are little systematic data collected on urban wood fuels in general). In terms of deforestation, there are two bigger culprits than wood fuel cutters and charcoal producers: timber companies and small farmers, who are driven by different types of motivation, the first for profit and the second for survival. Both produce products for the growing populations in the cities. To do so, they clear woodland and fell trees. The wood produced as part of the process, together with that created by urban expansion, creates a resource for urban fuel.
There is also an urban-energy-water nexus. Water, through large-scale dams, is a provider of electrical energy for urban areas. It is estimated that Africa holds 10% of the world’s hydro potential energy at 1100 tWh (Theuri, 2006) and yet only 4% of the continent’s technical potential has been tapped (Bartle, 2002). Given the small percentage of the population in Africa with access to electricity and the compelling need to mitigate climate change, the pressure to develop hydro-electricity in Africa will increase. Dams are known to significantly disrupt river function, inundate ecosystems and reduce down stream flooding (Acreman, 1996). The construction of dams not only destroys habitats but also creates new ones, particularly for freshwater snails that are a vector for schistosomiasis (Lerer & Scudder, 1999). The increase in schistosomiasis in Africa is strongly linked to dam construction although many of the dams are for small-scale irrigation projects and not for electricity generation (Savioli et al., 1997). Increases in malaria have also been reported (Ghebreyesus et al., 1999; Lerer & Scudder, 1999). Large-scale dams create additional ecological problems when their construction leads to the displacement of people who are pushed to marginal areas, which in turn can disrupt ecosystems through use of natural resources from unfamiliar settings (Showers, 2002).
Human urban ecology
The urban environment can be particularly polluted in terms of air quality and waste disposal. All urban dwellers are affected by air pollution caused by transport and industry but the degree of exposure has a strong linkage to income levels. Exposure to air pollution comes from three sources: (i) direct exposure to indoor air pollution (IAP) from using poor quality fuels in confined spaces; (ii) direct exposure in the work place; and (iii) indirect exposure because of inadequate urban planning. Urban homes generally use biomass fuels (and in Southern Africa coal) for their cooking and hot water needs, although high-income households may use liquefied petroleum gas (LPG) and electricity. Biomass fuels are typically burnt in open fires or poorly functioning stoves, often indoors with inadequate ventilation. Poor conversion efficiencies lead to very high levels of indoor pollution, with especially women and young children exposed on a daily basis. Smoke from these fuels contains many pollutants, which are known to be capable of irritating the airways and lungs, reducing the resistance to infection and increasing the risk of cancer, particularly in women (Bruce, undated). Evidence has begun to emerge, which suggests that IAP in developing countries may also increase the risk of other important child health problems, such as low birth weight, perinatal mortality, asthma and middle ear infection (Bruce, Perez-Padilla & Alablak, 2000).
There are little data available about the effects of exposure in the work place in Africa but it is not unreasonable to assume that those employed in modern industries and factories will face similar types of hazards as workers in industrial countries. The Air Pollution Information Network for Africa (APINA) considers that thousands of people in Southern Africa are likely to be exposed to levels of pollutants well in excess of the World Health Organisation’s (WHO) guidelines. Measurements at a smelter in Kitwe, Zambia, show that the employees have a mean weekly exposure to sulphur dioxide concentrations in excess of 2000 μg m−3 whereas the WHO guideline based on a 10-min exposure is 500 μg m−3 and the Zambian guideline for 1-h exposure is 350 μg m−3 (APINA, 2003).
However, the majority of urban workers tend to find employment in the unregulated informal sector. Many of the informal sector enterprises are using process heat generated by unprocessed biofuels and residual oil products. There appears to be little research into the consequences of occupational exposure to local level pollution in informal sector enterprises. An additional hazard is created when entrepreneurs use discarded oil drums as make-shift combustion devices, for example in urban fish smoking communities in Lagos, Nigeria, which burn fuelwood in old oil drums. Women stand smoking fish for 7 h a day and are exposed not only to the wood smoke but also to other pollutants of unknown toxicity from residual oil (Maduka, 2006). Many informal retail outfits are located along the side of roads where the entrepreneur is exposed to exhaust fumes from transport for several hours a day. There are other injuries associated with the urban woodfuel chain. A study in Addis Ababa found that fuel gatherers, who often carry loads nearly equal to their own body weight, frequently suffer falls and bone fractures; eye problems; headaches; rheumatism; anaemia; chest, back and internal disorders; and miscarriages (Haile, 1991).
Over 90% of air pollution in cities in Africa is attributed to vehicle emissions brought about by the high number of older vehicles coupled with poor maintenance, inadequate infrastructure and low fuel quality. In this regard, the UNEP led initiative begun in 2001 to eliminate lead in petrol is to be welcomed (Anon, 2003). As of July 2008, only four African countries were selling only unleaded petrol (http://www.lead.org.au/fs/fst27.html; accessed 18 October 2008). Pollution from power stations burning fossil fuels is dispersed by air currents and can be deposited in rural areas causing damage to habitats. As early as 1988, The Council for Scientific and Industrial Research in South Africa was reporting forest damage related to air pollution in the northeast Transvaal (APINA, 2003).
The disposal of water after domestic or industrial use in urban Africa is not well documented (Showers, 2002). Sewage treatment appears to be rare and often inadequate. Most domestic and industrial effluents are disposed of in streams or oceans. A small number of urban areas in semi-arid or arid locations use treated waste water for irrigation (Showers, 2002). On a positive note, sewage treatment in Gaborone, Botswana uses lagoons, which have become a new habitat for water birds in what is essentially a desert environment and is now an important site for bird watching (Showers, 2002).
The amount of solid household waste that the ‘average’ African urban dweller produces is less than that of the ‘average’ OECD citizen (0.5–0.8 kg per person per day and 1–2 kg per person per day, respectively) (UNEP, undated). However, it is how the waste is disposed of that is of considerable ecological concern. Urban solid waste generally ends up in landfill sites, which are usually open dumps placed without consideration to the ecological or hydrological conditions (UNEP, undated). There are no systems installed for leachate or gas recovery, which would help to reduce the environmental impacts.
Reducing the urban energy ecological footprint: the wood fuel issue
How can we reduce the energy ecological footprint of urban Africa? Possibly, the most obvious issue to address is wood fuels for household use. Given the levels of IAP, why, given that there are readily available supplies of alternatives in urban areas, such as kerosene and LPG, do people not use these alternatives? The factors which affect fuel switching are complex. Relative prices play a major role in the choice of fuel. Even though many poor urban households buy their fuels, using up to a quarter of their cash income (Barnes, 1995), the price difference between woodfuels and the alternatives continues to be sufficiently large that it keeps the alternatives out of reach. However, even when the price difference favours the alternatives, switching does not always happen. A study in Niger found that despite cooking with kerosene being cheaper than with wood, wood was still the preferred fuel (Leach & Mearns, 1988). Three reasons were cited: (i) the power output of the kerosene stove was significantly lower than the traditional wood fire, and so cooking took longer time; (ii) the kerosene stove did not support the round-bottomed cooking pots used in the area, which tended to overbalance during the frequent stirring necessary with staple local foods; and (iii) the kerosene stoves were not robust.
The unreliability of LPG supply has been identified as a significant barrier to switching from wood fuel. The limited availability of the appropriate appliances for use with the new fuels can also act as a barrier (Hosier & Kipondya, 1993). A very important reason why people continue to cook on wood fuel is the taste imparted to food (Clancy et al., 2006). The taste created by wood fuel is much more acceptable than that from kerosene. Trying to change human behaviour is notoriously difficult.
However, policymakers have risen to the challenge of reducing urban wood fuel use with a number of approaches. In Addis Ababa, Ethiopia, switching to modern fuels has occurred as a direct result of government policies to reduce the environmental impacts of clearing peri-urban forests to meet the demands of urban fuel supply. Wood accounted for 13% of the total energy used in 2000, compared with 70% in 1980 (Shanko & Rouse, 2005). While the environmental benefits of such policies are not to be denied, the socio-economic impacts are less certain. The number of people involved in supplying urban wood fuel can be quite significant; wood fuel production/distribution has become an important source of income for urban poor in Zimbabwe, Mozambique, Zambia and Malawi (Mika L, Practical Action Southern Africa, Pers. Comm.). In Addis Ababa, on a single market day in 1984, 42,000 suppliers were counted transporting traditional fuels into the city. However, by 2001, the number of suppliers had dropped to 3500 as a consequence of the government’s policies referred above. There appears to have been no simultaneous effort by the government to address the loss of livelihoods. There is a tacit assumption that ‘the market’ will provide these. It was estimated that in Addis Ababa, around 2000 jobs have been created by small businesses manufacturing electric, kerosene and improved biomass-stoves (Shanko & Rouse, 2005), which leaves a considerable gap to bridge for people with few skills appropriate for employment in modern manufacturing and services.
Substitution of wood fuel by fossil fuels, such as LPG, while reducing exposure to smoke may not reduce overall deforestation. In Africa, peri-urban deforestation is more likely to be caused by land clearance for agriculture to produce crops for growing urban markets (and peri-urban expansion) with charcoal production as a by-product. Leach and Mearns considered that the premise that stopping the use of wood fuel would halt deforestation is based on a false understanding of the sources of wood fuel (Leach & Mearns, 1988). The solution to the deforestation problem lies in the agriculture and forestry sectors, as well as in urban planning.
Another alternative policy approach is to accept that woodfuel use in urban areas is not going to go away and to make the supply more sustainable. There are signs that this approach is becoming more acceptable as a viable policy option and decision-makers are beginning to review policies to identify the best way forward to achieve a sustainable wood supply. The ‘fortress forest’ approach is considered to have failed and community forest management is seen as a corner-stone of policies to slow deforestation. Public sector foresters need to move to an integrated environmental services approach, which not only produces wood but also ensures other important environmental objectives such as protection of watersheds and biodiversity are achieved.
From an ecological viewpoint, switching to fossil fuels adds to the ecological footprint. The use of fossil fuels is a short- to medium-term strategy as the price of petroleum fuels has increased significantly in the last few years and the signs are that the trend will continue upwards. This makes the transition from wood fuels to fossil fuels less likely, particularly for poor people, and strengthens the argument for more sustainable wood fuel production.
At first glance, Africa is doing better than the rest of the world in terms of ecological footprints. However, this is no reason for complacency. The aggregate figures hide a reality that is a considerable cause for ecological concern. The ecological footprints of Africa’s cities have a very significant impact on rural ecosystems. It is worrying that there is a lack of data on these impacts. For example, in an extensive review of urban–rural water linkages in Africa, Showers (2002: 622) concluded that there is a ‘paucity of information about water before or after it enters urban infrastructure’. The same can be said about urban wood fuel use.
Technical solutions are readily available to reduce the urban impact on rural areas but nontechnical factors are often the barrier to their implementation. At the individual level, it is usually the cost of alternatives that prevents a transition away from wood fuels. While a shift to fossil fuels would reduce IAP, there are two important points to take into account: first, shifting to fossil fuels increases the ecological footprint and, secondly, it is unlikely to have a major impact on halting deforestation (although there may be some localized benefits). There is a considerable body of opinion, which contests the view that charcoal production is responsible for forest degradation. Therefore, it is important for policy makers to recognize that banning charcoal production will not halt the destruction of habitats, indeed, banning charcoal production is counterproductive. Bans, without alternative sources of income generation for many poor rural and urban people, will not work. Bans drive charcoal producers away from managed solutions, making production difficult to control and to encourage a transition to more sustainable production methods (Girard, 2002). It is more effective to work together with communities to develop sustainable systems. Indigenous knowledge can make an important contribution to ensuring sustainability.
Urban growth in Africa is of interest to ecologists: not only because of the threats to habitats, eco-systems and biodiversity that urban settlements bring but also for the new habitats and eco-systems that are created when providing services for urban dwellers. Ecologists also have a contribution to make in solving some of the health problems that these new habitats can bring. Human urban ecology also faces challenges which, if overcome, can have positive impacts on rural habitats.