Brazil's population is highly concentrated in cities, and there are many problems, such as

traffic jam

traffic problems have always been one of the primary problems in big cities. The rapid urbanization and the rapid expansion of population in big cities make the contradiction between urban traffic demand and traffic supply increasingly prominent, which is mainly manifested in traffic congestion and a series of problems such as pollution and safety. In London, there are a lot of government agencies, courts, enterprises, financial institutions and entertainment places in the downtown area, and there are more than 1 million jobs. Every day, more than 1 million people and 4, motor vehicles enter and leave the downtown area during peak hours, resulting in serious traffic congestion in this area. The average speed in this area is only 14.3 km/h, making it the most crowded area in Britain. In Paris, in the 196s, due to the adoption of the policy of "adapting to the development of cars", the number of private cars increased day by day, which led to serious traffic jams in the urban area. In 1973, the expressway around the city appeared persistent congestion shortly after it was opened. In Bangkok, because of the slow speed, the whole city is like a parking lot, and even 9 pregnant women were forced to give birth in cars because of traffic jams within three months. Traffic congestion will not only lead to the decline of economic and social functions, but also lead to the continuous deterioration of urban living environment and become a "chronic urban disease" that hinders development. The most direct impact of traffic congestion on social life is to increase the travel time and cost of residents. The increase of travel cost not only affects work efficiency, but also inhibits people's daily activities, which greatly reduces the vitality of the city and the quality of life of residents. In addition, traffic congestion has also led to an increase in accidents, which in turn aggravated the congestion. According to relevant statistics, the economic losses caused by traffic accidents in Europe reach as much as $5 billion every year. Third, traffic congestion also destroys the urban environment. With the rapid growth of motor vehicles, traffic pollution to the environment is also increasing, and it has gradually become the main source of pollution for the deterioration of urban environmental quality. According to the test report of London in 199s, 74% of nitrogen oxides in the atmosphere come from automobile exhaust emissions. Traffic congestion causes vehicles to travel only at low speed. Frequent stopping and starting not only increases the energy consumption of vehicles, but also increases the exhaust emissions and noise. According to the analysis of traffic conditions in big cities in developed countries by British SYSTRA Company, the cost of economic growth caused by traffic congestion accounts for about 2% of GDP, the cost of traffic accidents accounts for about 1.5-2% of GDP, the cost of traffic noise pollution accounts for about .3% of GDP, the cost of automobile air pollution accounts for about .4% of GDP, and the cost of automobile air pollution transferred to other regions accounts for about 1-1% of GDP.

environmental deterioration

in the past century, with global warming as the main feature, great changes have taken place in the global climate and environment, such as water shortage, ecosystem degradation, intensified soil erosion, sharp decline in biodiversity, ozone layer depletion and changes in atmospheric chemical composition. According to the prediction of the Intergovernmental Panel on Climate Change, the global warming will continue at a faster speed in the future, and the temperature will increase by 1.4℃ ~ 5.8℃ in the next 1 years, which will bring more serious impacts on the global environment, such as the deterioration of crop environment will reduce production, the frequency and speed of pests and diseases will increase obviously, and the shortage of water resources will worsen. Environmental pollution makes the city turn from traditional public health problems (such as water-borne diseases, malnutrition, lack of medical services, etc.) to modern health crisis, including air pollution, noise, vibration and mental stress caused by industry and traffic. Environmental pollution has a great impact on urban economy. The World Bank once estimated that the health cost and productivity loss caused by pollution are equivalent to about 1% to 5% of GDP.

shortage of resources

shortage of water resources

At the World Summit on Sustainable Development held in South Africa in p>22, it was unanimously approved that water resources should be listed as one of the most serious challenges facing mankind in the next decade. In the same year, the United Nations Environment Programme pointed out in the Global Environment Outlook that "at present, half of the rivers in the world have been greatly reduced or seriously polluted, and more than 8 countries or 4% of the world's population are seriously short of water. If this trend is not contained, more than 55% of the world's population will face water shortage in the next 3 years. " Among water-deficient countries or regions, the water shortage in big cities is the most serious. According to the prediction of relevant United Nations agencies, by 21, large and medium-sized cities in both developing and developed countries, including Beijing, Shanghai, Houston, Jakarta, Los Angeles, Warsaw, Cairo, Lagos, Dhaka, S? o Paulo, Mexico City and Singapore, will all face serious water shortages. In addition, the shortage of land resources is also an inevitable problem in the process of urbanization in international metropolises. Because of the absolute rigidity of land supply, in the process of a large number of people and industries gathering in the central city, some metropolises, such as Tokyo, new york, London and so on, have encountered serious land shortage problems, and the restriction of land on the sustainable development of modern metropolises is more prominent. How to open up new development space and expand regional scope has become an inevitable requirement for major cities to achieve sustainable development.

urban poverty

Slum problem is a unique phenomenon in the process of accelerating urbanization in large and medium-sized cities in developing countries. Most of the poor people are concentrated in cities, and most of the urban poor live in slums, such as Mumbai, India and Sao Paulo, Brazil. On the one hand, most slum dwellers are living in the poverty line, unable to enjoy the fruits of economic and social development as citizens, and their living, travel, health and education conditions are extremely poor, which not only affects the development of contemporary people, but also affects the development of the next generation. On the other hand, the huge difference in living standards has caused the estrangement of national feelings. In addition, slums are separated from community and normal social management, and some slums are controlled by the underworld and become dens of urban crime. In 19, 1.5 million of new york's nearly 4 million people lived in 43, slums. Until the 21st century, new york still had Harlem slums. At present, 6% of Mumbai's 16 million people live in slums and simple buildings on the roadside, which account for only one tenth of the urban land area. Slums have become the biggest feature of this world-famous port city and India's economic center city. Urban disease

The appearance of slums is largely caused by the influx of foreign population and the excessive income gap of the population in this city. There are mainly the following reasons: First, the serious inequality of land ownership has caused a large number of landless farmers. Take Brazil as an example, most of Brazil's land has been controlled by a few big landlords, and a large number of landless farmers have migrated to cities, and this flow is one-way, so they can't flow back to the countryside. Second, there is a serious shortage of employment opportunities in the process of urbanization. Unemployment, underemployment and poor quality of employment are important reasons for the long-term existence of a large number of urban poor people. In the process of urbanization, developing countries often shift their industrial focus to capital-and technology-intensive sectors, resulting in a large number of laborers entering the traditional service industry and the informal sector in the tertiary industry. In general, the wages in the informal employment sector are only half of those of the formal sector. There is no labor contract, no social security and no legal protection. Third, urban planning, land for building, infrastructure and community development have not fully considered the requirements of low-income people. 8% of people living in urban slums earn less than the minimum wage, so it is difficult for them to obtain land and housing for building houses in cities, and they can't return to the countryside. They can only illegally seize urban public land (such as hilltops and public land in urban-rural fringe) and private land, build humble houses and engage in illegal construction. Fourth, the public policy is not perfect. For example, the national education expenditure is excessively inclined to secondary and higher education, and the primary education is relatively shrinking. In the secondary education stage, attention is paid to general education and humanities education, while secondary vocational and technical education and normal education are ignored, which is not conducive to improving the education and employment situation of children of low-income classes.