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 city dwellers 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 also often suffer from polluted air and flooding. They 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.
The Guidance on Integrated Urban Hydro-Meteorological, Climate and Environmental Services (IUS), developed by a WMO inter-programme working group and the Commission for Atmospheric Sciences and Commission for Basic Systems, documents and shares the good practices that will allow countries and cities to improve the resilience of urban areas to a great variety of natural and other hazards.
- Volume I: Concept and Methodology; adopted by the 70th WMO Executive Council
- Volume II: Demonstration Cities; adopted by the 71st WMO Executive Council