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World Resources 1996-97 (A joint publication by The World Resource Institute, The United Nations Environment Programme, The United Nations Development Programme, and the World Bank) (Data edited by Dr. Róbinson Rojas)
3. Urban Impacts on Natural Resources EXTRACTION AND DEPLETION OF NATURAL RESOURCES
Cities require vast quantities of resources to run--both for urban inhabitants and for the economic activities that are clustered there. In contrast to rural communities, which are immediately dependent on the land that supports them, urban communities are rarely confronted with the impacts of their resource consumption-- advanced transportation networks allow resources to be tapped from distant hinterlands. Rich cities, in particular, draw on resources far from their boundaries.
The demand for supplies for cities is much greater and more complex than ever before. These supplies range from such basics as water, fuel, sand, and wood, to minerals such as aluminum and steel, to advanced plastics and synthetic materials. For instance, urban expansion creates demands for construction materials such as clays, sand, gravel, and crushed rock to make concrete, cement, and road stone (54). In Aligarh City, India, approximately 1,000 cubic meters of soil is brought into the city each day, altering natural drainage channels and increasing the level of flooding of large areas in the region (55). In Jakarta, Indonesia, 1.2 million cubic meters of wood, mainly from the nearby rural islands of Kalimantan and Sumatra, is imported to the metropolitan region each year (56). The process of resource extraction can also have negative environmental impacts, altering natural habitats, increasing land degradation, and indirectly leading to pollution, such as in mining discharges or saline intrusion into aquifers.
The range of inputs that sustain city life is enormous, and a discussion of all of these inputs is beyond the scope of this report. However, a discussion of two resources--water and energy-- illustrates how the scale of urban demand can deplete local resource stores.
Energy Resources Patterns of Energy Use
Urbanization has a profound effect on the amount and type of energy consumed. Along with population growth, economic development, and industrialization, urbanization is one of the principal forces driving the global increase in energy demand (57) (58). Although traditional rural societies rely heavily on human and animal energy and on nearby wood for fuel, today's urban societies are characterized by their reliance on fossil fuels and electricity. These different patterns of energy use lead to different environmental impacts.
In the developing world, per capita energy consumption remains low. For many urban dwellers, especially in smaller cities in Africa and Asia, a large share of energy needs are still met by biomass fuels (59) (60). As these countries urbanize, however, demand for energy increases and traditional, bulky fuels such as wood or charcoal are replaced by oil and electricity (61) (62). Energy consumption tends to be greater in urban areas in the developing world as urban households acquire more appliances, such as irons, televisions, and refrigerators (63). Urban dwellers are more likely to travel to work via energy-intensive modes of transportation, and food and other materials consumed in urban areas must be transported across greater distances (64). Urban manufacturing and industry are more energy intensive than traditional farming (65). Building the urban infrastructure necessary to support the high population densities in cities requires energy not typically expended in traditional rural settlements (66) (67) (68).
By contrast, per capita energy use in urban areas of the developed world tends to be lower than that in rural areas (69). Part of the reason is that industries are no longer located strictly in cities (70), but much has to do with the efficiencies of scale possible in cities. For example, attached housing and apartment buildings require less energy for heating and cooling, and mass transit requires less energy than transport by personal car (71). Far greater amounts of energy would be required to provide similar services to dispersed rural populations than to concentrated urban populations.
Impacts of Resource Extraction
In the developing world, biomass fuels provide between 25 and 90 percent of domestic energy supplies, especially in smaller urban centers (72). Although urban consumption of wood as fuel is neither the primary use for forest products nor the major cause of forest loss globally, local impacts on nearby forests can be severe. Even in cities with low levels of per capita consumption of biomass fuels--Bangkok, Thailand, and Manila, Philippines, for example--the large number of people concentrated in a small area can place considerable total demand on forest resources (73).
The growth in demand for wood resources around cities has caused deforestation around some urban centers reaching 100 kilometers and more. In India between 1960 and 1986, the closed forest cover around 18 urban centers decreased between one fifth and two thirds (74). In Africa, urban regions are now experiencing rapid rates of deforestation (75), as in the peri-urban region of Ouagadougou, Burkina Faso, and the subhumid wooded savannah around Dar es Salaam, Tanzania (76). Deforestation also contributes to a variety of indirect environmental impacts, including soil degradation, water siltation, and the loss of indigenous plant and animal species (77). However, since forests are a renewable resource, proper management can help mitigate the impacts; indeed, in some cases the scarcity of fuelwood has led to additional tree planting (78).
As a fuel source, charcoal is often preferred over wood because of its compact size. However, pressures on forests can intensify when urban households switch from wood to charcoal because charcoal is produced at low conversion efficiencies from wood (79) (80). In Senegal, for example, charcoal production accounts for the clearing of between 18,000 and 33,000 hectares per year, or between 11 and 20 percent of total estimated annual deforestation (81). This percentage of annual deforestation can be attributed primarily to urban resource demands, since in urban areas charcoal accounts for 91 percent of wood-based fuels compared with 8 percent in the rural areas (82).
As cities increase their reliance on fossil fuels and electric power, pressure on surrounding forests decreases but new problems emerge, often at considerable distances from the city itself. The environmental impacts of, for example, coal mining and oil and gas drilling and transport can be severe (83). In Katowice, Poland, for example, local coal mines are causing water and land degradation. In 1992, Katowice's coal mines discharged more than 4,800 metric tons of salt into the Vistula River each day, leading to major declines in aquatic life (84) (85). About 20,000 hectares of land in the region are degraded (up from 9,500 hectares in 1975) by mining excavations, tunnels, land subsidence, waste dumps, and flooded areas. Each year, 500 to 600 hectares of additional land is degraded; in 1988, only 74 hectares was reclaimed (86) (87).
Many countries, including those with enormous amounts of available water, face urban water supply problems (88). Local water shortages are especially acute in the world's megacities, although they are also appearing in smaller urban agglomerations such as Dakar, Senegal; Lima, Peru; La Rioja, Spain; and Lucknow, India.
The growing demand for water, along with poor water resource management and mounting pollution levels, contributes to water supply problems in and around cities. Although municipal water use accounts for less than one tenth of the world's overall water use (89), urbanization increases the per capita demand for water for domestic purposes. Part of this growth in demand can be attributed to better access to water supplies in cities than in rural areas. Industrial demand for water also rises. As the number of people in urban areas grows, so does the demand for food and, hence, for irrigation in agricultural areas close to the city. These pressures can quickly result in demands for water that surpass local water supplies.
Poor urban water management practices exacerbate local water shortages. Where water rights are not clearly defined, users may claim supplies well in excess of their needs to deal with future uncertainties. Water is usually priced much lower than the actual cost of securing, treating, and distributing it (in part because of government subsidies), leaving little incentive for households and industries to conserve water. Inefficient water systems are another major source of water loss. In many cities in the developing world, leaky pipes and illegal connections waste between 20 and 50 percent of public water supplies (90) (91). (See Figure 3.2.) In developed countries, aging infrastructure is contributing to similar problems. In the United Kingdom, as much as 25 percent of all water used may be lost because of leakage (92).
Water scarcity is closely linked to water quality. Freshwater lakes and rivers provide affordable and easily accessible water, but uncontrolled discharges of domestic sewage and industrial effluents have left many urban rivers heavily polluted and their water unsafe for use. Consequently, cities must search for water supplies well beyond their boundaries (93).
Other cities rely on groundwater, but many of them are withdrawing water from aquifers faster than natural rates of replenishment, leading to salinization and subsidence. (See Box 3.1.) Saline intrusion is common in almost all coastal cities, from Jacksonville, Florida, to Dakar, Senegal, to the Chinese cities of Dalian, Qingdao, Yantai, and Beihai (94) (95) (96). Land subsidence can cause structural damage to buildings and roads and can contribute to urban flooding. For Bangkok, which overdraws water from its aquifer by a conservative estimate of 0.6 million to 0.8 million cubic meters per day, the compacting of underlying soils has led to land subsidence ranging from 5 to more than 10 centimeters per year throughout the region (97). To alleviate this land subsidence, Bangkok would have to reduce its groundwater extraction rate by at least one half--a formidable challenge because water demand is expected to grow rapidly in the coming decades (98).
Water shortages and conflicts among urban, industrial, and agricultural users may become especially severe in parts of India, China, and the Middle Eastern nations. Much of sub-Saharan Africa is likely to face similar pressures, although data for the region are scarce. Already struggling with uneven distribution of water resources and local water scarcity, the urban populations of these regions are expected to double in less than 25 years (99).
In India, total demand for water is projected to nearly double by 2025. Although agriculture will still claim the bulk of water supplies, demand is growing fastest in the urban and industrial sectors and is projected to climb 135 percent over the next 40 years (100). Already in Hyderabad, India, the need for irrigation water during low-flow years is in direct conflict with the need for water within the city itself. Similar conflicts are emerging in China, where about 300 cities already experience water shortages (101).