| Summary: | Green roofs can help with stormwater management and reduce the risk of flooding. Most studies on the hydrological abilities of green roofs have been conducted in temperate climates. There is therefore a need to also investigate this in cold climates. The purpose of the thesis is therefore to clarify whether the capabilities of green roofs also work in the Nordic climate. This was done by studying runoff data from two green roofs located in Umeå, and Kiruna. Modeling was also used to study factors that are difficult to change and test in practice. Precipitation and runoff data from the green roofs were analyzed to calculate their retention abilities during precipitation events. The retention ability is defined as the percentage of precipitation that does not flow through the green roof. When analyzing precipitation and runoff, an "event-by-event" method was used, which meant that the data was divided into different events based on predetermined criteria. 109 events were identified. The factors evaluated through modeling were roof slope, substrate depth and width. Simulations were carried out in the EPA SWMM software where the different factors were varied in a model of the green roof in Umeå. Differences in runoff during the simulations were noted to draw conclusions about which values of the various factors result in the best retention. The study of the two green roofs results in an average retention capacity of 63.1% for the green roof in Umeå, as well as 68.5% for the roof section KB1 and 59.7% for KB2 in Kiruna. It can therefore be concluded that both roofs can reduce the flow of runoff water in the event of precipitation. The simulations result in the green roof's retention capacity being positively affected by a higher substrate depth. However, the retention capacity of the roof is not affected by its roof slope or width.
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