Sprawl or compactness? How urban form influences urban surface temperatures in Europe

The surface of cities is often warmer than the surface of their surroundings. This phenomenon is known as the surface urban heat island (SUHI) effect and has several adverse implications. Studies have shown that the SUHI effect tends to be weaker if urban form is characterized by sprawl or polycentrism. These findings suggest that urban heat could be mitigated if a city is less compact. By analyzing high-resolution remote-sensing land surface temperature (LST) and land-cover data for 293 European cities, this study shows that — contrary to many previous findings — sprawling or polycentric urban forms do not necessarily lead to a decrease of LSTs over urban areas. In southern European cities, sprawl could even lead to the warming of urban areas during specific daytimes, highlighting the importance of considering environmental and regional contexts when determining the role of urban form in heat mitigation. It is also crucial to consider the predominant type of land cover surrounding a city since sprawl into forested areas could have a very different effect than sprawl into agricultural areas. These results illustrate the complexity of urban form related heat mitigation and that policy- and decision-makers have to consider local and regional contexts when steering urban form.