The impact of urbanization and climate change on urban temperatures: a systematic review

Context Cities have elevated temperatures compared to rural areas, a phenomenon known as the "urban heat island''. Higher temperatures increase the risk of heat-related mortality, which will be exacerbated by climate change. Objectives To examine the impact of climate change and urban growth on future urban temperatures and the potential for increased heat stress on urban residents. Methods We conducted a systematic review of scientific articles from Jan 2000 to May 2016. Results The majority (n = 49, = 86%) of studies examined climate change and the urban heat island in isolation, with few (8) considering their combined effect. Urban growth was found to have a large impact on local temperatures, in some cases by up to 5 degrees C in North-east USA. In some locations climate change increased the heat island, such as Chicago and Beijing, and in others decreased it, such as Paris and Brussels. When the relative impact of both factors was considered, the temperature increase associated with the urban heat island was always higher. Few studies (9) considered heat stress and its consequences for urban populations. Important contributors to urban temperatures, such as variation in urban density and anthropogenic heat release, were often excluded from studies. Conclusions We identify a need for an increased research focus on (1) urban growth impact on the urban heat island in climate change studies; (2) heat stress; and, (3) variation in urban density and its impacts on anthropogenic heat. Focussing on only one factor, climate change or urban growth, risks underestimating future urban temperatures and hampering adaptation.