United Nations data show that the world’s population living in urban areas rose from 29 per cent in 1950 to 50 per cent in 2010; this is expected to grow to 69 per cent in 2050. The number of mega-cities – with a population of 10 million people or more – has grown from 2 in 1950 (New York City and Tokyo) to 19 in 2007. This is expected to rise to 26 by 2025, with many of them located in developing countries.
Cities have a great need for historical information for planning as well as data and weather, climate and environmental forecasts for real-time decision-making.
Emissions and hazards
Cities and urban areas use about 75 per cent of the world’s energy and are responsible for 75 per cent of greenhouse gas emissions.
Analysis of weather, climate and water factors is critical to supplying the input needs of cities, managing their liveability and sustainability and reducing the risks and costs of natural hazards.
Three-quarters of all large cities are located in coastal regions. Globally, 60 per cent of the world’s population lives in Low Elevation Coastal Zones (less than 10 metres above sea level), which are potentially vulnerable to sea level rise. Low Elevation Coastal Zones represent 2 per cent of the world’s area, but 10 per cent of its population. Coastal zones are the most urbanized with 80 per cent of coastal populations living in cities. Fourteen of the world’s 19 largest cities are port cities, according to UN-Habitat.
Extreme weather events and climate change underscore the need to involve meteorological and hydrological services in urban planning and engineering, infrastructure development, beach management and coastal defences to face future challenges.
Planning for city transportation and energy generation and distribution systems needs to accommodate not just average conditions, but also extremes like blizzards when services are under greatest pressure.
Gradual rises in sea level are becoming a problem for cities near to oceans, especially during tropical cyclones and storm-related events. Poorer areas with inadequate drainage are especially vulnerable. Further, coastal cities have major port facilities that need to deal with floods and storm surges. Public road systems and major international airports are also often located at sea level.
Water needs and risks
Almost all big cities face major fresh water challenges because of excessive groundwater withdrawal and disruptions to supply. Cities in subtropical dry zones, including Mexico City, Delhi and Dhaka, are likely to feel water stress from more frequent droughts and higher temperatures in their catchments.
Hydrologists, climate scientists and weather forecasters therefore need to work closely to develop water management strategies for mega-cities. Many planners are already making adjustments. For example, the government of Pune, India, which lies in a flood-prone area, has developed a programme of measures to reduce energy use and improve drainage systems. Similarly, the Greater London Authority is implementing the London Climate Change Adaptation Strategy that adopts a risk-based approach to the main impact of flooding, drought and overheating.
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