The urban climate of the largest cities of the European Arctic

Recent studies have found intense and persistent positive temperature anomalies associated with urban areas in high northern latitudes. However, understanding the intensity and variability of urban heat islands (UHI) in these regions remains limited. Here we study the urban climate of the seven largest cities in the European Arctic. These cities with populations ranging from 50,000 to nearly 300,000 span four countries and three bioclimatic zones in northern Fennoscandia. They include coastal and inland cities—and have complex local geography associated with topography and water bodies. We analyze land surface temperature (LST) satellite remote-sensing data with the Moderate Resolution Imaging Spectroradiometer (MODIS) from 2000 to 2020. The aim is to assess the intensity and temporal (seasonal and interannual) variability and trends of LST anomalies to learn about surface UHI development over different time frames in the urban Arctic. We observed persistent urban temperature anomalies in every season in the range of 1–5 °C, with the highest values for the largest city Murmansk (Russia). There is a strong inverse relationship between surface UHI intensity and its temporal variability: the more substantial the surface UHI, the more stable it is and the lower its temporal variability. Murmansk and Tromsø (Norway) have the highest thermal anomalies showing relatively low temporal variability, whereas the surface UHI in Bodø (Norway) is low and very volatile. We found no general direction of surface UHI change in the long term, as statistically significant changes were identified for only 10 of 56 cases. The study also suggests that in addition to the size (population) of the city, the presence of compact and dense urban infrastructure causes strong and stable urban temperature anomalies and has a more significant impact than the geographical setting of the city.