Editing Urban heat island (section)

=== Diurnal variability ===
[[File:Urban heat island variation.jpg|upright=1.55|thumb|Cities often experience stronger urban heat island effects at night; effects can vary with location and topography of metropolitan areas.]]
Throughout the daytime, particularly when the skies are cloudless, urban surfaces are warmed by the absorption of [[solar radiation]]. Surfaces in the urban areas tend to warm faster than those of the surrounding rural areas. By virtue of their high [[Heat capacity|heat capacities]], urban surfaces act as a reservoir of heat energy. For example, concrete can hold roughly 2,000 times as much heat as an equivalent volume of air.{{citation needed|date=July 2024}} As a result, high daytime surface temperatures within the UHI can be easily seen via thermal [[remote sensing]]. As is often the case with daytime heating, this warming also has the effect of generating [[Atmospheric convection|convective]] winds within the urban [[Planetary boundary layer|boundary layer]]. At night, the situation reverses. The absence of solar heating leads to the decrease of atmospheric convection and the stabilization of urban boundary layer. If enough stabilization occurs, an [[Inversion (meteorology)|inversion layer]] is formed. This traps urban air near the surface, keeping surface air warm from the still-warm urban surfaces, resulting in warmer nighttime air temperatures within the UHI.

Generally speaking, the difference in temperature between the urban and surrounding rural area is more pronounced at night than in daytime.<ref>{{Cite web |title=Urban Heat Islands {{!}} Center for Science Education |url=https://scied.ucar.edu/learning-zone/climate-change-impacts/urban-heat-islands |access-date=2024-07-02 |website=scied.ucar.edu}}</ref> For example, in the United States, the temperature in urban areas tends to be warmer than the surrounding area by about 1–7 °F (0.55–3.9 °C) during the daytime, and about  2–5 °F (1.1–2.8 °C) warmer at night.<ref name=":22">{{Cite web |last=US Envrionmental Protection Agency |first=OAR |date=2014-06-17 |title=Learn About Heat Islands |url=https://www.epa.gov/heatislands/learn-about-heat-islands |access-date=2024-07-01 |website=www.epa.gov |language=en}}</ref> However, the difference is more pronounced during the day in arid climates such as those in southeastern China and Taiwan.<ref>{{Cite journal |last1=Zhou |first1=Decheng |last2=Zhang |first2=Liangxia |last3=Hao |first3=Lu |last4=Sun |first4=Ge |last5=Liu |first5=Yongqiang |last6=Zhu |first6=Chao |date=2016 |title=Spatiotemporal trends of urban heat island effect along the urban development intensity gradient in China |url=https://doi.org/10.1016/j.scitotenv.2015.11.168 |journal=Science of the Total Environment |volume=544 |pages=617–626 |doi=10.1016/j.scitotenv.2015.11.168 |pmid=26674691 |bibcode=2016ScTEn.544..617Z |issn=0048-9697}}</ref><ref>{{Cite journal |last1=Liou |first1=Yuei-An |last2=Tran |first2=Duy-Phien |last3=Nguyen |first3=Kim-Anh |date=2022-02-22 |title=Diurnal and Seasonal Characteristics of Surface Urban Heat Island in Taiwan |url=https://easychair.org/publications/preprint/MjGx |journal=(CETA 2021) 2021 International Conference on Computer Engineering, Technologies and Applications |language=en-US |issn=2516-2314}}</ref> Studies have shown that diurnal variability is impacted by several factors including local climate and weather, seasonality, humidity, vegetation, surfaces, and materials in the built environment.<ref>{{Cite journal |last1=Amorim |first1=Margarete Cristiane de Costa Trindade |last2=Dubreuil |first2=Vincent |last3=Amorim |first3=Amanda Trindade |date=2021 |title=Day and night surface and atmospheric heat islands in a continental and temperate tropical environment |url=https://doi.org/10.1016/j.uclim.2021.100918 |journal=Urban Climate |volume=38 |pages=100918 |doi=10.1016/j.uclim.2021.100918 |bibcode=2021UrbCl..3800918A |issn=2212-0955}}</ref><ref name=":22" /><ref>{{Cite journal |last1=Shastri |first1=Hiteshri |last2=Barik |first2=Beas |last3=Ghosh |first3=Subimal |last4=Venkataraman |first4=Chandra |last5=Sadavarte |first5=Pankaj |date=2017-01-09 |title=Flip flop of Day-night and Summer-Winter Surface Urban Heat Island Intensity in India |journal=Scientific Reports |language=en |volume=7 |issue=1 |pages=40178 |doi=10.1038/srep40178 |pmid=28067276 |issn=2045-2322|pmc=5220321 |bibcode=2017NatSR...740178S }}</ref><ref>{{Cite journal |last1=Mohajerani |first1=Abbas |last2=Bakaric |first2=Jason |last3=Jeffrey-Bailey |first3=Tristan |date=2017-07-15 |title=The urban heat island effect, its causes, and mitigation, with reference to the thermal properties of asphalt concrete |url=https://www.sciencedirect.com/science/article/pii/S0301479717303201 |journal=Journal of Environmental Management |volume=197 |pages=522–538 |doi=10.1016/j.jenvman.2017.03.095 |pmid=28412623 |bibcode=2017JEnvM.197..522M |issn=0301-4797}}</ref>