Measures for the improvement of human thermal comfort in typical street canyons within highly dense neighborhoods in the context of heat stress in Hamburg

Abstract

Adaptation to climate change is one of the pressing issues that many cities will need to include in their development plans. Due to its oceanic climate, Hamburg is recognized by its windy and rainy seasons. Nevertheless, global warming and highly dense cities are causing the increase of urban heat island (UHI) effect and Hamburgers can already feel that today in the form of heat stress. Sunny summer days are long awaited opportunities to spend quality time outdoors in Hamburg. However, open spaces can quickly overheat and become unpleasant if not well designed. Due to their specific geometry, streets are known to block winds and capture heat. That is described by Oke (1981) as a typical street canyon (SC) effect of ‘delayed cooling’, when at night time facades release temperature gained during the day and such process takes longer than in open spaces. After a detailed urban analysis, a representative street canyon in the central Hamburg area was selected as the main unit for further thermal comfort assessment. Outdoor thermal comfort is determined by air temperature, mean radiant temperature, solar radiation, humidity, wind speed and direction, metabolic rate and clothing insulation. Physical elements of street canyons include adjacent buildings, street surfaces as well as urban green infrastructure. Through a detailed analysis of street canyon geometry and surface materials, thermal comfort was assessed by mean radiant temperature and universal thermal climate index (UTCI). With the help of mean radiant assessment tool (MRAT) and UTCI online platform, 24 different scenarios were tested. The results showed that moderate to strong heat stress is already present in Hamburg’s streets. This thesis investigates mean radiant temperature and outdoor thermal comfort at the level of street canyon with a goal of proposing effective adaptation measures during periods of heat stress. If implemented on a bigger scale, proposed measures can influence the UHI of an entire city. Additionally, the measures proposed for Hamburg’s streets are applicable in cities with similar climates and urban densities. By further refinement and implementation in zoning plans, the measures can be formalized and therefore, their effects ensured.