Project funded by the National Science Center

Urban Heat Island

As of 2022, the world's population is more than 8 billion, of which about 57% people live in cities. 

The urban population is estimated to increase by 2 people every second. It currently stands at more than 4 billion and will grow to 6.5 billion by 2050.
As a result of the impact of urban development, among other things, urban areas are characterized by distinct climatic conditions compared to non-urban areas. The city's climate is characterized by, among other things, increased air pollution, higher air temperature, higher precipitation totals, as well as more days with fog and lower wind speed.
A local climatic phenomenon occurring in the city is the urban heat island (UHI). Its manifestation is an increase in air temperature in the ground layer of the atmosphere in the city relative to the surrounding peripheral areas.
Such conditions are a consequence of the accumulation of a large amount of artificial surfaces in the city, which absorb more solar radiation than they reflect. In addition, this phenomenon is influenced by a smaller proportion of vegetated areas and weaker ventilation, as well as the emission of anthropogenic heat into the atmosphere produced by heating and air-conditioning equipment, automobile traffic, etc.
The characteristics of an urban heat island depend on the size and spatial structure of the city and the population. The name of this phenomenon is related to the course of isotherms, which on the city plan assume a shape similar to the contour of an island surrounded by a sea of cooler air (Figure 1).
Figure 1. Annual average UHI intensity in urban areas of Beijing (left) - values for 2007-2010 (source: Yang et al. 2013) and UHI index calculated for Warsaw (right) - values for 2011-2012 (source: Blazejczyk et al. 2016).
In the absence of accurate data on the spatial distribution of urban air temperature, a frequently used measure of the urban heat island is its intensity. It is calculated as the difference in air temperature between the urban center and the non-urban area. 

The urban heat island is a dynamic phenomenon characterized by high daily and annual variability. The greatest differences in air temperature between urban and non-urban areas are observed during bright and cloudless nights. The spatial extent of the heat island corresponds to the area of urban development.
The urban heat island was first recognized by L. Howard in London and was described in an 1833 book titled "The City of London. Climate of London deduced from meteorological observation made in metropolis and at various places around it

L. Howard presented a comparison of air temperature in London and out-of-town areas based on observations from 1807-1816. In subsequent years, similar studies were conducted in other regions of Europe, such as in Paris by E. Renou, in Vienna by W. Schmidt, and in Munich by A. Schmauss.
On the other hand, in the Polish literature, references to the characteristics of the climate of cities can be found in Merecki's 1915 work, in which he pointed out the reduction in solar totals in Warsaw relative to non-urban areas by about 100 hours. However, the urban heat island phenomenon began to be addressed in detail only since the late 1950s.

Literature

Błażejczyk K., Kuchcik M., Milewski P., Dudek W., Kręcisz B., Błażejczyk A., Szmyd J., Degórska B., Pałczyński C. (2014). Miejska wyspa ciepła w Warszawie. Uwarunkowania klimatyczne i urbanistyczne. Wydawnictwo Akademickie Sedno sp. z o.o. Warszawa. (in Polish)

Błażejczyk K., Kuchcik M., Dudek W.,Kręcisz B., Błażejczyk A., Milewski P., Szmyd J., and Pałczyński C. (2016) Urban Heat Island and Bioclimatic Comfort in Warsaw. [in:] Counteracting Urban Heat Island Effects in a Global Climate Change Scenario; Musco F. (ed.), Springer International Publishing: Cham, Switzerland, 305-321 ISBN 978-3-3-319-10424-9.

Fortuniak K. (2003). Miejska wyspa ciepła. Podstawy energetyczne, studia eksperymentalne, modele numeryczne i statystyczne. Wydawnictwo Uniwersytetu Łódzkiego, Łódź. (in Polish)

Majkowska A., Kolendowicz L., Półrolniczak M. et al. (2017). The urban heat island in the city of Poznań as derived from Landsat 5 TM. Theoretical and Applied Climatology 128, 769-783.

Tamulewicz J. (1997). Wielka encyklopedia geografii świata t.5. Wydawnictwo Kurpisz. (in Polish)

Yang, P., G. Ren, and W. Liu, 2013: Spatial and Temporal Characteristics of Beijing Urban Heat Island Intensity. J. Appl. Meteor. Climatol., 52, 1803-1816.
Research project on how urban development affects the intensity of urban heat islands.
Funding
National Science Center
Grant number 2023/48/Q/HS4/00147
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