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Urban Heat Island

Urban heat islands are regions around cities that experience higher temperatures as a result of energy use, lack of convection or evaporation due to loss of vegetation, and features such as roofs and pavement that absorb more heat than natural land.

Extent

On average, heat islands add several degrees Celsius to large cities.

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Sources: heat island effect in world cities by Estrada et al. 1, US cities estimated by Imhoff et al. 2, and humid and dry cities by Zhao et al. 3.

The urban heat island effect tends to be greater in larger, more compact, and more circular (as opposed to elongated) cities 4.

The urban heat island effect is responsible for 2-4% of observed global warming, with the rest caused by greenhouse gases and black carbon (79% and 18% respectively) 5.

Impact

About 166,000 people die every year from heat waves 6, which cause health problems including respitory issues, heat stroke, and others 7. Estimates for how many of these deaths can be attributed to urban heat islands varies considerably.

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Sources: 8, 9.

The urban heat island effect has been estimated to cause about $270 million (2020 US dollars) of net present value damage in Melbourne, Australia 10. Worldwide, it may cost about 3.4% of GDP in 2100 1. The effect costs 14 large cities an estimated 0.068% of GDP in extra air conditioning costs alone 11.

Urban heat islands have been linked with fish deaths 7, among other ecological impacts.

Mitigation

The urban heat island effect can be mitigated by increasing a city's reflectivity, such as through white roofs, and by planting more vegetation. Both strategies were found to have benefit-cost ratios greater than 1 in Austria 12. Such strategies were also found to save lives through reducing the severity of heat waves in Washington, D. C. 13.

Problem:
Urban Heat Island
Solution:
Heat Mitigation Through Trees - World

Shade, both from trees and from buildings, helps reduce the urban head island effect 14. Other strategies include green roofs and walls, reflecting roofs, cooler or less pavement, water fixtures such as fountains, and urban designs to facilitate passive cooling 15.

References

  1. Estrada, F., Wouter Botzen W. J., Tol R. S. J. "A global economic assessment of city policies to reduce climate change impacts". Nature Climate Change 7, pp. 403-406. May 2017. ↩ ↩2

  2. Imhoff, M. I., Zhang, P., Wolfe, R. E., Bounoua, L. "Remote sensing of the urban heat island effect across biomes in the continental USA". Remote Sensing of Environment 114(3), pp. 504-513. March 2010. ↩

  3. Zhao, L., Lee, X., Smith, R. B., Oleson, K. "Strong contributions of local background climate to urban heat islands". Nature 511, pp. 216-219. July 2014. ↩

  4. Zhou, B., Rybski, D., Kropp, J. P. "The role of city size and urban form in the surface urban heat island". Scientific Reports 7: 4791. July 2017. ↩

  5. Jacobson, M. Z., Ten Hoeve J. E. "Effects of Urban Surfaces and White Roofs on Global and Regional Climate". Journal of Climate 25(3), pp. 1028-1044. February 2012. ↩

  6. World Health Organization. "Heatwaves". Accessed April 22, 2021. ↩

  7. United States Environmental Protection Agency. "Heat Island Impacts". Accessed April 22, 2021. ↩ ↩2

  8. Dang, T. N., Van, D. Q., Kusaka, H., Seposo, X. T., Honda, Y. "Green Space and Deaths Attributable to the Urban Heat Island Effect in Ho Chi Minh City". American journal of public health 108(S2), pp. S137-S143. April 2018. ↩

  9. Heaviside, C., Vardoulakis, S., Cai, X. "Attribution of mortality to the urban heat island during heatwaves in the West Midlands, UK". Environmental Health 15: S27. March 2016. ↩

  10. AECOM Australia Pty Ltd. "Economic Assessment of the Urban Heat Island Effect". Prepared for City of Melbourne. November 2012. ↩

  11. Miner, M. J., Taylor, R. A., Jones, C., Phelan, P. E. "Efficiency, economics, and the urban heat island". Environment and Urbanization 29(1), pp. 183-194. April 2017. ↩

  12. Johnson, D., See, L., Oswald, S. M., Prokop, G., Krisztin, T. "A cost–benefit analysis of implementing urban heat island adaptation measures in small- and medium-sized cities in Austria". Environment and Planning B: Urban Analytics and City Science. December 2020. ↩

  13. Kalkstein, L. S., Sailor, D., Shickman, K., Sheridan, S., Vanos, J. "Assessing the Health Impacts of Urban Heat Island Reduction Strategies in the District of Columbia". Global Cool Cities Alliance. October 2013. ↩

  14. Park Y., Guldmann J. M., Liu D. "Impacts of tree and building shades on the urban heat island: Combining remote sensing, 3D digital city and spatial regression approaches". Computers, Environment and Urban Systems 88:101665. July 2021. ↩

  15. Williams, J. "7 ways to reduce the urban heat island effect". The Earthbound Report. July 2021. ↩