Urban heat island

This article is about higher temperatures in cities due to urbanization effects. For effects of climate change on city temperatures, see climate change and cities.
Example of dense urban living without green spaces which leads to a pronounced urban heat island effect (Milan, Italy)
Example of an inner city green space which can reduce the urban heat island effect (Central Park, New York)

Urban areas usually experience the urban heat island (UHI) effect, that is, they are significantly warmer than surrounding rural areas. The temperature difference is usually larger at night than during the day,[1] and is most apparent when winds are weak, under block conditions, noticeably during the summer and winter. The main cause of the UHI effect is from the modification of land surfaces while waste heat generated by energy usage is a secondary contributor.[2][3][4] Urban areas occupy about 0.5% of the Earth's land surface but host more than half of the world's population.[5] As a population center grows, it tends to expand its area and increase its average temperature. The term heat island is also used; the term can be used to refer to any area that is relatively hotter than the surrounding, but generally refers to human-disturbed areas.[6]

Monthly rainfall is greater downwind of cities, partially due to the UHI. Increases in heat within urban centers increases the length of growing seasons and decreases the occurrence of weak tornadoes. The UHI decreases air quality by increasing the production of pollutants such as ozone, and decreases water quality as warmer waters flow into area streams and put stress on their ecosystems.

Not all cities have a distinct urban heat island, and the heat island characteristics depend strongly on the background climate of the area in which the city is located.[7] The impact in a city can change a lot based on its local environment. Heat can be reduced by tree cover and green space which act as sources of shade and promote evaporative cooling.[8] Other options include green roofs, passive daytime radiative cooling applications, and the use of lighter-colored surfaces and less absorptive building materials. These reflect more sunlight and absorb less heat.[9][10][11]

Climate change is not the cause of urban heat islands but it is causing more frequent and more intense heat waves which in turn amplify the urban heat island effect in cities.[12]: 993  Compact, dense urban development may increase the urban heat island effect, leading to higher temperatures and increased exposure.[13]

  1. ^ Phelan, Patrick E.; Kaloush, Kamil; Miner, Mark; Golden, Jay; Phelan, Bernadette; Silva, Humberto; Taylor, Robert A. (4 November 2015). "Urban Heat Island: Mechanisms, Implications, and Possible Remedies". Annual Review of Environment and Resources. 40 (1): 285–307. doi:10.1146/annurev-environ-102014-021155. S2CID 154497357.
  2. ^ Solecki, William D.; Rosenzweig, Cynthia; Parshall, Lily; Pope, Greg; Clark, Maria; Cox, Jennifer; Wiencke, Mary (2005). "Mitigation of the heat island effect in urban New Jersey". Global Environmental Change Part B: Environmental Hazards. 6 (1): 39–49. doi:10.1016/j.hazards.2004.12.002. S2CID 153841143.
  3. ^ United States Environmental Protection Agency (2008). Reducing urban heat islands: Compendium of strategies (Report). pp. 7–12.
  4. ^ Li, Y.; Zhao, X. (2012). "An empirical study of the impact of human activity on long-term temperature change in China: A perspective from energy consumption". Journal of Geophysical Research. 117 (D17): D17117. Bibcode:2012JGRD..11717117L. doi:10.1029/2012JD018132.
  5. ^ Wang, K (February 6, 2017). "Comparing the diurnal and seasonal variabilities of atmospheric, and surface urban heat islands based on the Beijing Urban Meteorological Network". Journal of Geophysical Research: Atmospheres. 122 (4): 2131–2154. Bibcode:2017JGRD..122.2131W. doi:10.1002/2016JD025304.
  6. ^ Glossary of Meteorology (2019). "Urban Heat Island". American Meteorological Society. Retrieved 2019-04-12.
  7. ^ T. Chakraborty and X. Lee (2019). "A simplified urban-extent algorithm to characterize surface urban heat islands on a global scale and examine vegetation control on their spatiotemporal variability". International Journal of Applied Earth Observation and Geoinformation. 74: 269–280. Bibcode:2019IJAEO..74..269C. doi:10.1016/j.jag.2018.09.015. S2CID 53715577.
  8. ^ Waldrop, M. Mitchell (19 October 2022). "What can cities do to survive extreme heat?". Knowable Magazine. doi:10.1146/knowable-101922-2. Retrieved 6 December 2022.
  9. ^ "Nature of Cities". Regeneration.org. Retrieved 2021-10-16.
  10. ^ Cite error: The named reference :2 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference :13 was invoked but never defined (see the help page).
  12. ^ "Cities, Settlements and Key Infrastructure". Climate Change 2022 – Impacts, Adaptation and Vulnerability. 2023. pp. 907–1040. doi:10.1017/9781009325844.008. ISBN 978-1-009-32584-4.
  13. ^ Sharifi, Ayyoob (2020). "Trade-offs and conflicts between urban climate change mitigation and adaptation measures: A literature review". Journal of Cleaner Production. 276: 122813. Bibcode:2020JCPro.27622813S. doi:10.1016/j.jclepro.2020.122813. S2CID 225638176.