Urban heat islands in cities

This case study by the Stockholm Environment Institute uses Pärnu City and County in Estonia to illustrate the development and impact of urban heat islands (UHI). It employs satellite-derived land surface temperature data and social vulnerability mapping to demonstrate how heat risk is an interaction between physical hazards, population exposure, and social sensitivity.

• Estonia has experienced a temperature increase of 0.2–0.3°C per decade since 1951, which exceeds the global average for that period. This trend has led to more frequent and intense extreme weather events, with significant heatwaves occurring in 2010, 2014, 2018, 2021, and 2022.
• Heatwaves cause significant premature mortality in Estonia's five largest cities, averaging more than 36 deaths per year. Vulnerable populations, including children, pregnant women, the elderly, and those with chronic diseases, are disproportionately affected.
• Urban heat islands (UHI) occur when hard surfaces like roads and buildings absorb heat and a lack of green space prevents cooling, making these areas significantly hotter than outskirts, especially at night. In Pärnu City, this is compounded by coastal dynamics where the Baltic Sea bay warms quickly in summer, creating some of the highest coastal water temperatures in northern Europe.
• Spatial analysis in Pärnu County shows that the highest heat proximity correlates with urban density. While peat mining areas also show elevated temperatures due to dark surfaces, they are considered less relevant to heat island risk because they lack human exposure.
• Heat risk is defined as the interaction between hazard, exposure, and vulnerability. In Pärnu, vulnerability is unevenly distributed, with high concentrations of sensitive groups—specifically adults aged 65+ and children under 10—located in the city centre and certain surrounding clusters.

APA

Hoy, A. (2026). Urban heat islands in cities. Stockholm Environment Institute. https://www.sei.org/features/urban-heat-islands-cities-storymap/

Chicago

Hoy, Andreas. Urban heat islands in cities. Stockholm Environment Institute, 2026. https://www.sei.org/features/urban-heat-islands-cities-storymap/.

Wikipedia

{{cite report |last1=Hoy |first1=Andreas |title=Urban heat islands in cities |publisher=Stockholm Environment Institute |date=9 January 2026 |url=https://www.sei.org/features/urban-heat-islands-cities-storymap/ |access-date=17 August 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{hoy2026urban, author = {Hoy, Andreas}, title = {{Urban heat islands in cities}}, institution = {Stockholm Environment Institute}, year = {2026}, month = jan, url = {https://www.sei.org/features/urban-heat-islands-cities-storymap/}, urldate = {2026-08-17}, note = {Indexed by Climate Insights Directory} }