In a subproject carried out together with the City of Stockholm within the HazardSupport research project, SMHI has investigated how town planning affects a city’s climate. Scenarios have been produced for Stockholm’s growth up until 2030 and 2050, using summer 2014 as a reference point. These scenarios do not take ongoing climate change into account. Instead, they simply show how the densification and growth of Stockholm can be expected to affect the air temperature.
The main conclusion from the scenarios is that the impact of densification on air temperature is relatively local. No significant effect on the average temperature during the summer is seen at a distance of more than about 2 km, despite extensive densification across large areas. This can be seen in the most central parts of Stockholm, for example, which are already built-up and where no significant reduction in green spaces can therefore be expected. No significant change in air temperature is seen in these areas.
One reason why the densification and expansion of Stockholm has not had any significant impact on air temperature is the relatively rapid air exchange with nearby expanses of water and countryside. Within those areas that are densifying, average summer temperature increases of up to around 1.5°C are being seen. As expected, the biggest temperature increases are observed when natural environments or green areas are built on.
Measures in the local area
One consequence of the locally limited effect of changes in the urban environment is that measures should primarily be focused on direct effects within the local area. Examples of such measures include shady street trees and proximity to green spaces. For the same reason, measures such as green roofs that only indirectly affect the air temperature in the street environment can be expected to have a less significant impact.
A comfort index can be used to summarise the effect of various climate parameters. One example of such an index is the Universal Thermal Climate Index (UTCI). This involves a higher level of ambition in relation to how climate planning is often carried out in today’s planning processes.