Reduced Urban Heat Island intensity under warmer conditions

Abstract

The Urban Heat Island (UHI), the tendency for urban areas to be hotter than rural regions, represents a significant health concern in summer as urban populations are exposed to elevated temperatures. A number of studies suggest that the UHI increases during warmer conditions, however there has been no investigation of this for a large ensemble of cities. Here we compare urban and rural temperatures in 54 US cities for 2000-2015 and show that the intensity of the urban heat island, measured here as the differences in daily-minimum or daily-maximum temperatures between urban and rural stations or Δ, in fact tends to decrease with increasing temperature in most cities (38/54). This holds when investigating daily variability, heat extremes, and variability across climate zones and is primarily driven by changes in rural areas. We relate this change to large-scale or synoptic weather conditions, and find that the lowest Δ nights occur during moist weather conditions. We also find that warming cities have not experienced an increasing urban heat island effect.

Interaction of urban heat islands and heat waves under current and future climate conditions and their mitigation using green and cool roofs in New York City and Phoenix, Arizona

“…ΔT 2 can be 4°C larger in Phoenix during pre-and post-heat wave periods, leaves a large uncertainty on the synergistic interaction between future climate and UHI under heat waves. A recent study (Scott et al 2018) compared daily minimum air temperatures in 54 US cities for 2000-2015 and suggested that UHI reduces under warmer conditions. It also looked at 15 hottest nights during 2000-2015 and found weaker UHIs during heat waves.…”

“…It also looked at 15 hottest nights during 2000-2015 and found weaker UHIs during heat waves. Based on the results, Scott et al (2018) suggested that the synergistic interaction between heat wave and UHI found by Li and Bou-Zeid (2013) is atypical. Schatz and Kucharik (2015) showed that in Madison, UHI estimated from daily maximum air temperature shows a much clearer increasing trend than UHI from daily minimum air temperature.…”

High‐resolution projections of extreme heat in New York City

“…Others have found evidence of UHI intensification during heat waves in Madison, WI (1.8°C daytime, 5.3°C night‐time; Schatz and Kucharik, ). However, Scott et al () showed in a multi‐city, multi‐year study that in 70% of the cities analysed, rural temperatures increased faster than urban temperatures, leading to lower UHI magnitudes during warm days. This underscores the need for studies of the underlying land surface processes that determine urban temperatures during hot days and how they vary across different regions and urban forms.…”

Star-shaped cities alleviate trade-off between climate change mitigation and adaptation

“…Green areas are commonly more abundant in leafy suburbs, compared to built-up inner cities. More compact cities tend to increase the UHI effect (Zhou et al 2017) and consequently worsen the impact of deadly heat waves (Mora et al 2017) (even if UHIs may often be of lower magnitude under warming conditions Scott et al 2018). While the UHI effect has positive effects in winter months in cities that have considerable heating demand, the impact of heat on health is emerging as one of the key and most harmful impacts of climate change (Gasparrini et al 2017).…”