Summer in the city: islands and heat waves

High temperatures in cities: causes and how to temper them

January 17, 2022

The recent heat wave that hit Argentina, Chile, Uruguay, and southern Brazil in the first weeks of January hoarded news and comments for days. Although in the southern hemisphere it is summer and high temperatures are expected, in the cities particularly this phenomenon put us in front of the effects of climate change.

In cities, there is the phenomenon called “urban heat island”. Heat island occurs in cities because, as they grow, they replace open spaces, vegetation, trees, and shady spaces with cement, asphalt, and hard soils.

These materials absorb the solar radiation and accumulate it during the day, releasing it during the night. Non-urban areas manage to lower the temperature during the night in the absence of solar radiation, while in the cities the accumulated during the day must dissipate during the night, resulting in hot nights. It results in a greater accumulation of heat in cities than in peripheries.

Other factors that influence cities to accumulate heat have to do with:

  • the combustion activities and processes that take place in the city: transport, lighting, heating, cooling.
  • changes in wind speed due to the phenomenon of construction and geometry of the city.
  • vertical construction, which causes heat to stay close to the ground
  • the least amount of green spaces, vegetation, shaded spaces, and bodies of water such as lakes, lagoons, streams, which would contribute to thermoregulation.
Phenomena multiply

As explained in the study by Alejandro Saez Reale of CIPPEC, although heat waves are non-permanent climatic events that are not directly related to urbanization, when they are simultaneous they act together: urban heat islands amplify the phenomenon of the heatwave, directly affecting the life of the city.

Some consequences of the urban heat island phenomenon that impact the environment and its inhabitants, both people and the rest of the biodiversity, are:

  • Climate change: temperatures, precipitation rate
  • Smog, pollutant emissions, and greenhouse gases
  • Runoff problems and the possibility of flooding
  • Reduced comfort and even health problems
  • Additional costs: demand for electricity and water supply
  • Impact on biodiversity: changes in species migration and flowering rates
Mitigation actions

The increase of trees, vegetation, the use of pavements, and fresh surfaces contribute to avoiding the accumulation of radiation and facilitate its dissipation.

  • Planting trees is one of the most effective ways to reduce the temperature in summer. According to ONU-Habitat, cities do not have enough green space, nor are they equally distributed, especially in informal slum areas.
  • Increase vegetation, green public spaces, install green roofs in buildings and homes.
  • Install cool ceilings with covers painted with light colors and avoid dark ones.
  • Increase the shady spaces, with the creation of galleries and overlays that give shadows over the houses and the streets.
  • Decrease the density and height of buildings
  • Use cold flooring, like ceilings, light colors. There is permeable concrete that could be applied to streets and avenues, which allow water filtration, reducing the risk of flooding and recharging the aquifers.
  • Promote public transport and that it moves away from the use of fossil fuels. Also, encourage the use of alternative transport such as bicycles.
Towards a sustainable future

The built environment contributes almost 40% of carbon emissions. Investments in green space can also help cities achieve broader sustainability goals, such as net-zero carbon.


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