Innsbruck’s urban heat island using measurements from the national weather service and a low-cost sensor network (I-UHI)

Urban heat stress is becoming an increasingly important topic. The well-known urban heat island (UHI) effect can reach up to 10 °C in large cities and affects a huge number of people: in Europe around 75% of the population lives in urban areas. Moreover, heat stress is on the rise – the frequency and severity of heat waves is increasing, bringing increased risks to human health and well-being. Elevated nocturnal temperatures in cities can be especially problematic as they do not give residents a chance to physiologically recover from extreme heat during the day.

The urban heat island effect depends on several factors. It is primarily a result of differences in surface characteristics between urban and rural areas: the large thermal mass of building and paved areas means cities store a lot more heat during the day and release it slowly at night; dissipation of heat is hindered by buildings which act to trap longwave radiation close to the surface; and limited vegetation cover restricts evaporative cooling. In addition, energy use for human activities results in additional heat emissions.

The shape of the UHI typically resembles that of an island – peaking in the city centre and declining towards the edges. In reality, temperatures can vary from place to place. Urban parks and water bodies can be several degrees cooler and can have a cooling effect on their surroundings. The UHI is also dependent on weather conditions, being usually largest during periods with clear skies and low wind speeds. UHI studies for cities in hilly or mountainous terrain reveal an even more complex picture. Orography results in spatial and temporal features in the UHI that differ considerably from the well-known characteristics of UHIs in flat terrain.

This project will investigate the UHI and near-surface temperatures in the alpine city of Innsbruck. First, the urban-rural temperature difference will be calculated from two stations operated by the national weather service, which have been operational for over 30 years. This long-term dataset will allow investigation of annual, seasonal and diurnal variability in UHI. Second, spatial variability in and around the city will be studied using a network of low-cost temperature sensors that was deployed in 2017-2018. Temperature patterns over the whole year will be explored with regards to land cover, urban characteristics and terrain features.