Seite 2 von 4: Städte - Hitzeinseln

 PROBLEM - STÄDTE als HITZE-INSELN

"  Overview

Urban environments experience higher temperatures than their rural surroundings. These higher temperatures can negatively impact human health, including causing cardiovascular and respiratory disorders, as well as heat stroke. It is therefore crucial to lower heat stress in urban environments.

Background

An ‘urban heat island (UHI)’ is an urban area that is significantly warmer than its rural surroundings due to artificial infrastructure and human activities. Whilst urban areas have a higher proportion of paved ground, rural areas are covered in grass, crops, shrubs or forest. This vegetation helps to cool the air whereas asphalt and concrete absorb heat, causing temperatures to rise. Furthermore, buildings and narrow streets trap heat by reducing air flow. Human activities such as warming buildings and driving cars also add heat to surroundings.

All these factors contribute to the urban heat island effect, which is most pronounced during the night, when temperatures in urban areas can be up to 10°C higher than in rural areas. This is due to retained heat in structures such as buildings and roads being released during the night.

Larger cities tend to experience stronger heat stress; the centres of London and Paris, for example, regularly record temperatures of around 4°C higher than rural surroundings at night. Both of these cities, and many others around Europe and the world, experience heat stress that leads to public health issues.

Urban planners and local governments want to design strategies to reduce this heat stress. These strategies could involve increasing so-called green-blue infrastructure, including enhanced vegetation cover (for example through green roofs) and more water surface. But to make these changes, they need to know how temperature varies spatially within the urban environment that they are responsible for.

Solution

The spatial variation of temperature can be obtained using an urban climate model. Using C3S ERA5 climate reanalysis data on air temperature, specific humidity, relative humidity and wind speed, VITO applied the UrbClim® model to provide urban climate information for 100 European cities at a high spatial resolution of 100 metres. UrbClim® has been successfully used and validated for many cities worldwide.

The results of UrbClim® are available through the C3S Climate Data Store (CDS) and are used in a CDS application called ‘Urban heat island intensity for European cities from 2008 to 2017 derived from reanalysis’. This application enables users to visualise the urban heat island effect for 2008–2017 for any of the 100 cities covered by UrbClim®. Users can select either summer (June, July, August) or winter (December, January, February) for any year in this ten-year period. The app provides maps showing the annual average ‘UHI’ – defined as the temperature difference between any location and the rural average – for a selected year (day and night) and for the ten-year period from 2008 to 2017 (day and night).

 Conclusion

The urban heat island application is free and easy to use, making it useful for addressing the phenomena of urban heat islands and their impact on human health.

Besides showing locations at risk, the application also enables users to visualise the spatial distribution of cool spots in a city. This information – in combination with socioeconomic and population data – is being used by urban planners (for example in Brussels) to develop a network of accessible cool spots that are promoted during heatwaves.

The mapping information also supports the implementation of local adaptation actions, such as the heat-resilient renovation of public squares and parking lots (for example in Antwerp), the adaptation of existing streets, and the design of new building districts. In Antwerp, urban heat island information was even used to motivate the obligation of green roofs in the update of the urban building code.

To summarise, the application can be used by urban planners and local governments to motivate and design strategies to adapt to excessive heat stress. Furthermore, the free and open data is being taken up by the general public to justify their concerns about the local environment."

Quelle: COPERNICUS - Climate Change Services - Demonstrating heat stress in European cities - https://climate.copernicus.eu/demonstrating-heat-stress-european-cities