Time Evolution of the Surface Urban Heat Island

• Published in: Earth's future Vol. 9; no. 10
• Main Authors: Stewart, I. D., Krayenhoff, E. S., Voogt, J. A., Lachapelle, J. A., Allen, M. A., Broadbent, A. M.
• Format: Journal Article
• Language: English
• Published: Bognor Regis John Wiley & Sons, Inc 01.10.2021; Wiley
• Subjects: Atmospheric models; Cities; Climate; Climate models; Diurnal; Diurnal cycle; diurnal temperature cycle; Diurnal variations; Evolution; Heat; Heat islands; Islands; Remote sensing; Rural areas; Satellite imagery; Satellites; Surface temperature; Temperature effects; Thermal imaging; thermal remote sensing; Urban climate models; Urban climates; Urban environments; urban heat island; Urban heat islands; France
• ISSN: 2328-4277; 2328-4277
• DOI: 10.1029/2021EF002178

Atmospheric and surface urban heat islands (UHI) originate from common energetic processes, but the status of scientific knowledge on their time evolution is highly disparate. The diurnal cycles of atmospheric UHI are well known based on years of continuous measurements in cities; the cycles of surface UHI, however, cannot be measured continuously or in situ. In this article, we aim to reconcile these differences. We begin with a synthesis of previous work on the diurnal evolution of surface UHI, which leads to a novel but historically minded approach to the research problem. The approach involves a combination of microscale and mesoscale urban climate models, each of which is forced with universally described urban and rural surface parameters and atmospheric profiles. With these models, we produce theoretical time‐temperature curves for the surface UHI that are comparable to the classic curves of atmospheric UHI. This work prompts a critical look at the use of satellite thermal imagery to assess heat islands and heat risks in cities. To that end, we recommend new and more functional definitions of surface temperature. Conceptually, these represent “incomplete” temperatures defined by specific facets of the urban environment. Plain Language Summary Urban heat islands (UHI) refer to the added warmth in cities due to the abundance of buildings, vehicles, and paved ground. However, very little is known about the hourly and daily changes in the surface temperatures of the city. This is partly due to the technological difficulties of sampling surface temperatures in urban environments, and to the myriad of surface types in cities. In this article, we aim to overcome this difficulty by using a combination of urban climate models, which can replicate daily temperature cycles for the surface UHI. With these data, we recommend new indicators of surface temperature that more accurately describe the heat risks and building energy demands in cities. Key Points Three numerical climate models are used to characterize the diurnal evolution of the surface urban heat island Diurnal evolution of surface heat islands varies with regional climate, urban morphology, rural land cover, soil moisture, and wind speed Satellite‐based observations of surface heat islands are likely to overestimate (underestimate) actual daytime (nighttime) impacts