BY the year 2020, about 2 billion people - half the world's urban population - will be living in cities in the Asian and Pacific region.
"The expansion of metropolitan areas in the region, including the emergence of megacities, can lead to unprecedented levels of pollution and environmental degradation unless appropriate measures are taken," warns the 1992 annual report of the Asian Development Bank. Half world's megacities
Since 1950 the number of cities in the region with a population of 1 million or more has grown from 19 to 86 in 1990. By the turn of the century 12 of the 21 megacities in the world (each having a population of 10 million or more) will be in this region, the report says. Bombay, Calcutta, and Shanghai will each exceed 15 million.
The report attributes the rapid increase in urbanization to natural population growth and rural-urban migration. Between 1970 and 1990, natural population increases accounted for about 55 percent of the region's urban growth. The remainder was from rural-urban migration.
The growing level of urbanization has been a major driving force behind economic development in the Asia-Pacific region, the report notes. In most countries in the region, cities generated over half their national economic outputs and raised three-quarters of their national taxes. The study predicts that during the 1990s about 80 percent of the region's economic growth will come from its urban economies.
Even though the growth of urban economies raised the living standard for city residents, not all urban residents have benefited, the study says. All large cities have significant proportions of their populations living below the poverty line. In the 1980s, however, countries such as Indonesia, South Korea, Malaysia, and Thailand made progress in reducing poverty.
The shift from agrarian to urban-based economies in the region presents serious environmental problems such as overloaded infrastructure, traffic congestion, and pollution. For instance, in Manila production is constrained by electricity shortages; in Bangkok traffic congestion hinders the movement of goods and services.
Although many cities in the region have invested to improve water supply and sanitation, countries such as Bangladesh, Pakistan, and Thailand lack safe drinking water for urban residents, the study notes. Curbing pollution
Seven of the world's 20 most polluted cities are in Asia - Beijing, Calcutta, Guangzhou, Manila, Shanghai, Shenyang, and Xian. However, China is trying to reduce air pollution in cities such as Beijing and Shanghai by replacing coal burning with gas and electricity.
Asian countries also wrestle with inadequate solid waste disposal, pollution of urban waterways, and contamination of groundwater due to inadequate sewerage facilities. For example, overexploitation of fresh ground water in Bangkok is causing the city to sink 2 to 4 inches a year.
The study calls for massive investments to protect resources and to minimize environmental degradation. To finance urban environmental projects, by the end of 1992 the bank had provided loans totaling about $3 billion and technical assistance grants worth about $48 million.
Even though increasing urbanization is a normal process of development, governments must take measures "to ensure that urbanization is environmentally sustainable," the report advises.