World Meteorological Day

Sustainable cities

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.

Cities at work on weather, climate and water
	Public safety. NMHSs are generally responsible for providing warnings of approaching storms and other hazards to allow public authorities to take action such as closing transportation systems or evacuating parts of the city.
	Airports and seaports. NMHSs partner airport and seaport operators to help ensure safe, efficient and reliable operations. Services range from daily weather forecasts to specialized predictions of oil slick movements and volcanic ash cloud dispersal.
	Heating and air conditioning design. Historical temperature and humidity data are essential in the design of heating and air conditioning systems. Increasingly, wind and solar radiation data is being used to design buildings that require less heating and air conditioning.
	Building codes. Wind speed data can be analysed to estimate the strength of winds likely to be encountered in different parts of the city and for different heights of buildings. Likewise, snow depth data can be used to establish security criteria in regions where buildings have to be resistant to heavy snow packs.
	Water supply. Historical data is the main basis for designing public water supply systems, but droughts can still occur and storage reservoirs may fail to meet demand. Water system managers use meteorological and hydrological information, including seasonal climate forecasts to assess risks and make key decisions.
	Sustainability. Most initiatives on cleaner air and water, renewable energy and public transportation require information on weather, climate and water. Some require specific monitoring programmes, considered analysis and public education.

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