Greening the Grey: Assessing the Impact of Pocket Parks on the Local Microclimate in Amsterdam Using ENVI-MET V4

By Christopher Kurth

Abstract
Materials like buildings and roads tend to have higher air and surface temperatures than their rural surroundings. This phenomenon is described as the Urban Heat Island (UHI). Implementation of vegetation in the microclimate’s energy balance can be used as an effective cooling mechanism within urban areas. Especially during heat waves, the demand for energy for cooling is higher. The city of Amsterdam already implements small-sized urban parks within multiple neighbourhoods. The two goals are to green the city and to strengthen the social cohesion within a neighbourhood. While this process is organised as a bottom-up approach, it is still unclear how a neighbourhood can adapt heat efficient as possible.

Testing various combinations of resolution and extent for a default park design within ENVI-met v4 resulted in a most suitable combination of 2m spatial resolution and 150m spatial extent. With this model set-up the default pocket park design, inspired by the design of De Nieuwe Maan Park, was implemented within three study areas. The objective was to assess the impact of a default pocket park within the local microclimate of the neighbourhoods. Besides, various designs, which differ in vegetation height and density were tested for these three study areas.

The size of pocket parks was determinative for the spatial range of the cooling effect (i.e. a higher surface area causes a wider cooling effect). The absolute air temperature encountered the highest mitigation of 2.22 ⁰C for scenarios where the vegetation diversity and density were the highest, caused by higher shading effect and evapotranspiration rate. During the night the microclimate was less sensitive for a cooling effect, explained by a surplus of sensible heat flux within the surface layer and a relative lower vertical and horizontal air turbulence.

Overall this research shows that vegetation stimulates the mitigation of the UHI. The spatial range of cooling effect and the absolute temperature difference depends on the park surface area, vegetation diversity, and vegetation density.