Trees as heat stress mitigators. The frequency of heat and cold stress in a redevelopment area in Borås, Sweden

Abstract

As future climate is predicted to generate higher temperatures as well as more frequent extreme weather scenarios, it is essential to plan to mitigate the effects of climate change. In an attempt to mitigate one effect of climate change, this master’s thesis examines both the heat and cold stress at the area Pulsen in Borås Stad, both as the conditions are today, and after the implementation of a new detail plan. The thermal comfort was analysed using SOLWEIG, both on the present detail plan and on the new one, both during summer and winter. Using the new detail plan as the point of departure, the tool TreePlanter was used to “plant” trees in the most optimal place for heat stress mitigation. Afterwards, the thermal comfort was again analysed using SOLWEIG during both summer and winter; the analysis was repeated to see the effect of the trees after 5, 10 and 25 years. It was found that trees strongly enhance the thermal comfort on a hot summer day, and the bigger the trees are, the bigger their effect is. During winter, instead, trees both enhance and reduce the thermal comfort. In shade behind buildings, they enhance the thermal comfort, but in open areas they reduce the thermal comfort. The placement of the trees is crucial for their success in enhancing the thermal comfort during summer while avoiding the reduction of thermal comfort during winter.