Russian Journal of Earth Sciences Russian Journal of Earth Sciences Russian Journal of Earth Sciences 1681-1208 92997 10.2205/2026es001065 lnokiy ОРИГИНАЛЬНЫЕ СТАТЬИ ORIGINAL ARTICLES ОРИГИНАЛЬНЫЕ СТАТЬИ On a Possible Mechanism Forming the Nighttime Maximum of Urban Heat Island Intensity On a Possible Mechanism Forming the Nighttime Maximum of Urban Heat Island Intensity https://orcid.org/0000-0003-0607-234X Демежко Дмитрий Юрьевич Demezhko Dmitry Yurievich

доктор геолого-минералогических наук;

doctor of geological and mineralogical sciences;

 https://orcid.org/0000-0002-0881-1284 Горностаева Анастасия Александровна Gornostaeva Anastasiya Aleksandrovna free_ride_@mail.ru

кандидат физико-математических наук;

candidate of physical and mathematical sciences;

 https://orcid.org/0000-0002-5684-8786 Хацкевич Богдан Дмитриевич Khatskevich Bogdan Dmitrievich https://orcid.org/0009-0003-2438-7297 Факаева Нелли Рафаэлевна Fakaeva Nelly Rafaelevna ФГБУН Институт геофизики им. Ю.П. Булашевича Уральского отделения Российской академии наук Yekaterinburg Россия Bulashevich Institute of Geophysics, Ural Branch of RAS Yekaterinburg Russian Federation 29 07 2026 29 07 2026 26 3 ES3006 27 12 2024 06 10 2025 https://rjes.ru/en/nauka/article/92997/view

In most cities in the world, the daytime maximum of the urban heat island (UHI) intensity is observed after sunset. It is minimal around noon. We propose a new mechanism for the formation of the UHI intensity’s diurnal cycle that considers the phase shift between surface temperature variations in the city and surroundings. This phase shift occurs due to the difference in thermophysical structure of the subsurface in urban and rural areas. In the case of a homogeneous medium, the temperature maximum at the surface is observed π/4 later than the heat flux maximum at solar noon. With the presence of an upper layer having a low thermal conductivity compared to the underlying layers, the phase shift would be less than π/4. Such conditions are often observed in rural areas. The delay of the temperature variations in the city relative to those in the countryside leads to an even greater delay in the UHI intensity relative to the heat flux. This is probably the main reason for the UHI intensity’s diurnal variations being observed. The proposed mechanism was verified through the data obtained at weather stations in Yekaterinburg and its surroundings.

In most cities in the world, the daytime maximum of the urban heat island (UHI) intensity is observed after sunset. It is minimal around noon. We propose a new mechanism for the formation of the UHI intensity’s diurnal cycle that considers the phase shift between surface temperature variations in the city and surroundings. This phase shift occurs due to the difference in thermophysical structure of the subsurface in urban and rural areas. In the case of a homogeneous medium, the temperature maximum at the surface is observed π/4 later than the heat flux maximum at solar noon. With the presence of an upper layer having a low thermal conductivity compared to the underlying layers, the phase shift would be less than π/4. Such conditions are often observed in rural areas. The delay of the temperature variations in the city relative to those in the countryside leads to an even greater delay in the UHI intensity relative to the heat flux. This is probably the main reason for the UHI intensity’s diurnal variations being observed. The proposed mechanism was verified through the data obtained at weather stations in Yekaterinburg and its surroundings.

 urban heat island intensity diurnal cycle ground surface heat flux ground surface temperature solar radiation thermal effusivity thermal inertia urban heat island intensity diurnal cycle ground surface heat flux ground surface temperature solar radiation thermal effusivity thermal inertia This work was funded by the Russian Science Foundation (project No. 22-77-10018, https://rscf.ru/project/22-77-10018/). This work was funded by the Russian Science Foundation (project No. 22-77-10018, https://rscf.ru/project/22-77-10018/).

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