Squares in towns or cities are public places where people can spend time. Providing space for a variety of uses, they are therefore of key importance to the local population. In view of the increasing heat stress in urban areas, such squares need to be designed to be more resilient to the effects of climate change in order to sustainably improve thermal comfort and thus the quality of time spent there. As part of the BUOLUS project, temporary adaptation measures have already been implemented and monitored at the real-world laboratory square “Salzstadel” in Rosenheim. Among others, these include a partially-greened, multifunctional seating element.
To identify further suitable heat adaptation measures for the Salzstadel square, various scenarios were developed using the PALM-4U Urban climate model (see Figure 1). The focus of the climate simulations was on improving thermal comfort during the day and on cooling the square at night.
The relevant parameters considered were air and surface temperature, wind speed and direction and the UTCI comfort index (Universal Thermal Climate Index). The UTCI enables thermal outdoor daytime conditions to be comprehensively assessed and integrates meteorological parameters such as wind, average radiation and air temperature. A total of ten measures were studied. To this end, an original scenario (parking spaces with surfaces that were fully sealed up till 2009) with minimal effect was conceived together with an extreme scenario (simulation with comprehensive redesign) with maximal effect in order to classify the simulated impact of the various measures. This reference context is shown in Figure 2.
The results show that the original scenario with fully sealed surfaces and no trees leads to less favorable climatic conditions, while the extreme scenario shows significant improvements. Design measures on vertical surfaces, such as greening the façades of nearby buildings, had no appreciable effect on the target values considered. This is because the resolution chosen in the simulation program is too coarse to accurately depict the processes. Modifications to horizontal surface properties such as albedo and removal of the surface sealing proved to be more efficient. In particular, introducing water features, changing the use of the streets by removing the road surface, planting new trees and greening helped to improve thermal comfort and nighttime cooling.
It also became apparent that implementing measures throughout the whole square is more effective than implementing “selective” measures only in the center where people tend to gather. In addition, the measures need to be evaluated differently depending on the time of day, as they have different effects. For example, while large groups of trees provide shade and evaporative cooling during the day, they can impair air exchange at night and store heat under their canopy. To continue to design the square to meet the needs of the various user groups, whilst at the same time increasing the quality of the stay, a combination of measures was recommended on the basis of the simulation results, including water features and changing the use of the streets.
The simulations made it possible to test the practical suitability of PALM-4U and to gain valuable insights into the effectiveness of various urban planning measures for improving thermal comfort and night-time cooling. In principle, the measures can be transferred to squares in other towns or cities. However, they must be adapted to the local conditions because every town or city has its own microclimate, which in turn is heavily dependent on the urban structure and local wind conditions.
The results were displayed on posters in the Salzstadel square in the summer.
The following three graphs show a summary of the simulation results, the different scenarios, and more detailed information on the urban climate simulation.
Fraunhofer Institute for Building Physics IBP
