Urban development - Megacities

Urban development - Megacities

Some 3.5 billion people reside in urban areas. This number is projected to reach 6.3 billion by 2050, increasing from 50% to more than 70% of the world’s population. Cities are centres of creativity and economic progress but they also face many environmental challenges due mainly to air pollution and weather, climate and water-related hazards.

Since 2007, for the first time in history, the majority of the world's population has been living in urban areas. Megacities, typically defined as cities with a population of over 10 million, cover less than 0.2% of the Earth's land area, however, 1 person in 10 on our planet lives in a megacity. Most urban dwellers live in cities in developing and least-developed countries, often in informal settlements vulnerable to weather, climate and water-related hazards and facing elevated air pollution levels.

In large urban settlements, human activities greatly modify the environment, creating unique meteorological and climatological characteristics. The agglomeration of tall buildings, roadways, green spaces and concrete surfaces produces intricate rain, wind, heat and air-quality patterns. The hard surfaces can shape water flow and aggravate flood risks. The alignment of buildings can create local wind tunnels. Tiny particles emitted by traffic and industry can reduce air quality. The urban heat-island effect can raise temperatures by 5 oC to 10 oC, exacerbating heatwaves.

Populations in urban areas are particularly vulnerable to air pollution, weather extremes, including heatwaves, flooding, droughts and storm surge for those in coastal areas, and climate change impacts. Increasingly dense, complex and interdependent urban systems can leave cities exposed to a domino effect – where a single extreme event leads to general infrastructural breakdown – with lasting consequences. This very interdependence requires an integrated approach to urban weather, environment and climate services aimed at the city's inhabitants and decision-makers: from weather and climate predictions to actions with community involvement and in urban planning.

Integrated weather, climate, hydrology and related environment services for sustainable cities

The accelerating growth of urban populations, especially in developing countries, has become a driving force of human development. Crowded cities are centres of creativity and economic progress but, from polluted air to flooding and other climate impacts, they also face major weather, climate, water and environment-related challenges. Increasingly dense, complex and interdependent urban systems leave cities vulnerable: through a domino effect, a single extreme event can lead to a broad breakdown of a city’s infrastructure.

Meteorological and related services provide essential information and forecasts that can assist urban decision-makers to face these challenges. These services can be used by emergency managers to map out risks and provide early warnings. They can be used by transport departments to minimize emissions, health providers to prepare heat-action plans and responses to severe pollution events, and agriculture and clean-energy managers to optimize production. Water departments can rely on such services to implement integrated flood-management plans, and urban planners can use them for siting buildings and infrastructure where they will be less vulnerable to sea-level rrise and other climate change and environmental impacts.
WMO is promoting safe, healthy and resilient cities through the development of Urban Integrated Weather, Environment and Climate Services. The aim is to build urban services that meet the special needs of cities through a combination of dense observation networks, high-resolution forecasts, multi-hazard early warning systems, disaster management plans and climate services. This approach gives cities the tools they need to reduce emissions, build thriving and resilient communities and implement the UN Sustainable Development Goals.

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