"Agglomeration economies mean investment in large cities yields higher growth returns than dispersing funds to secondary cities"

"urban settlements and simplifi ed drainage systems inevitably fail, leading to fl ooding. A comprehensive response to fl ood management includes maintaining catchment cover, managing wetlands and river channels, and siting <2 20–50 Population in low elevation coastal zones (LECZ) (%) 2–5 >50 5–10 Landlocked countries/No data 10–20 Outside LECZ Inside LECZ Mega cities Map 2.1 At risk: Population and megacities concentrate in low-elevation coastal zones threatened by sea level rise and storm surges Source: United Nations 2008a. Note: Megacities in 2007 included Beijing, Bombay, Buenos Aires, Cairo, Calcutta, Dhaka, Istanbul, Karachi, Los Angeles, Manila, Mexico City, Moscow, New Delhi, New York, Osaka, Rio de Janeiro, São Paulo, Seoul, Shanghai, and Tokyo. Megacities are defi ned as urban areas with more than 10 million inhabitants. 92 WORLD DEVELOPMENT REPORT 2010 interventions show mixed results, however. The Arab Republic of Egypt’s attempt to cre- ate satellite cities to decongest Cairo never attracted the projected population and did little to stop population growth in Cairo, partly because of the lack of policies to pro- mote regional integration.37 Successful pol- icies facilitate concentration and migration during the early stages of urbanization and interurban connectivity during the later stages. Public investments in infrastructure are most effective when they increase social equity (through broader access to services) and integrate the urban space (through the transport system).38 Urbanization seldom is harmoni- ous, generating pollution and pockets of wrenching poverty and social dislocation. Today, urban areas in developing coun- tries are home to 746 million people liv- ing below the poverty line (a quarter of the world’s poor),39 and the urban poor suffer from more than low income and consump- tion. Overcrowding, insecure tenure, illegal settlements sited in landslide- and fl ood- prone areas, poor sanitation, unsafe hous- ing, inadequate nutrition, and poor health exacerbate the vulnerabilities of the 810 million people in urban slums.40 These many vulnerabilities call for com- prehensive improvements in urban planning and development. Government agencies, particularly local ones, can shape the adaptive capacity of households and busi- nesses (box 2.2). But action by community- based and nongovernmental organizations (NGOs) is also crucial, particularly those that build homes and directly provide ser- vices, as slum-dweller organizations do.41 Sound planning and regulation can identify high-risk zones in urban areas and allow low-income groups to fi nd safe and afford- able housing, as in Ilo, Peru, where local authorities safely accommodated a fi vefold increase in the population after 1960.42 But hard investments in infrastructure may also be required to protect urban zones, such as coastal cities in North Africa, with seawalls and embankments (box 2.3). A major risk for urban areas is fl ooding— often caused by buildings, infrastructure, and paved areas that prevent infi ltration, exacerbated by overwhelmed drainage sys- tems. In well-managed cities fl ooding is Climate change is only one of many factors that determine urban vulner- ability. For many coastal cities, migration increases the population exposed to rising sea levels, storm surges"