Global urban climatology: a meta-analysis of air temperature trends (1960–2009)

• Published in: NPJ climate and atmospheric science 2018-09, Vol.1 (1), Article 32
• Main Authors: Varquez, Alvin C. G., Kanda, Manabu
• Format: Article
• Language: English
• Subjects: 704/106/694/674; 704/158/858; Air temperature; Anthropogenic factors; Atmospheric Protection/Air Quality Control/Air Pollution; Atmospheric Sciences; Cities; Climate; Climate Change/Climate Change Impacts; Climatology; Diurnal; Earth and Environmental Science; Earth Sciences; Emissions; Enthalpy; Geophysics; Heat; Heat storage; Human factors; Inertia; Meta-analysis; Night; Sensible heat; Specific heat; Storage capacity; Technology assessment; Thermal resistance; Trends; Urban areas; Urban heat islands
• ISSN: 2397-3722; 2397-3722
• DOI: 10.1038/s41612-018-0042-8

Air temperature trends (1960–2009) based on stations in cities, minus those based on global surface temperature datasets, are defined herein as urban heat island (UHI) trends. Urban climate was examined globally by comparing UHI trends with indices of geophysical factors, including background climate, latitude, and diurnal temperature range (DTR) and indices of artificial factors, including anthropogenic heat emission (AHE) and population indices. Surprisingly, a better relationship was found between UHI trends and DTR—an integrated geophysical index representing thermal inertia—than with the indices of artificial factors. Thus, while an increase in sensible heat (mechanism 1) triggers UHI formation, this study infers that large thermal inertia (mechanism 2) contributes significantly on UHI. The correlation of UHI trends with other indices can be explained by both mechanisms. Climate: warming in cities linked to heat storage capacity of urban surfaces The capacity of urban areas to absorb heat largely explains the urban heat island (UHI) effect observed in global cities. Alvin CG Varquez and Manabu Kanda from Tokyo Institute of Technology, Japan, assess the trends in urban heat island effect from 1960 to 2009 in 286 cities globally. They find the UHI effect has increased in most cities by 1.38 °C per century on average, with a larger effect at night and a more pronounced trend at higher latitudes. Most UHI trends can be explained by the thermal inertia, a higher resistance to temperature changes of urban surfaces, with heat trapped during the day being released at night. Human factors such as heat emissions and population were not correlated to the trend, but further studies are needed to fully disentangle the interactions between all factors.