Modeling the Urban Heat Island in Gothenburg, Sweden: an analysis of the Urban Weather Generator Louise

Sammanfattning: Urban Heat Islands is a well-known phenomenon that has been observed in most cities around the globe. It is a night-time phenomenon occurring on calm and clear nights and is defined as the temperature difference between an urban area and its rural surroundings. As air temperatures are getting higher due to climate change, along with a global trend of urbanization, there is a need to identify the risks of urban heat to implement heat-mitigating measures. One method for modeling Urban Heat Islands is the Urban Weather Generator (UWG). This study aims to investigate the characteristics of the UWG and evaluate how well it performs in the city of Gothenburg, Sweden. A sensitivity analysis of the different input parameters was performed, as well as a model evaluation where modeled data was compared to observed air temperatures from five different sites around Gothenburg. Building density is the parameter that most influenced the modeled air temperatures, while vegetation had a low effect on the modeled results. The results of the model evaluation showed that the model estimates urban air temperatures well in built-up dense areas, while areas with a high fraction of vegetation were not captured efficiently by the model. In these areas, the modeled air temperature was higher than the observed. Therefore, one can conclude that the model performs well in estimating air temperatures in typical urban environments, while it needs improvements in capturing the mitigating effects of urban vegetation.