Greening Cities: a Strategy against Extreme Heat

In recent weeks, many Mexican cities have faced more extreme heat waves than in previous years. While this phenomenon is closely related to climate change, it is also the result of urbanization processes that have replaced large areas of vegetation cover—such as forest areas, green areas, etc.—with concrete and asphalt. These materials retain much more heat than natural soils, generating what is known as heat islands: areas where the air temperature is significantly higher than in surrounding areas with greater vegetation cover.

International evidence helps to dimension this phenomenon. In the United States—where there is more evidence on this issue—the organization Trust for Public Land has documented that urban parks with a high density of vegetation can be up to 17 degrees Fahrenheit (9.4 degrees Celsius) cooler than adjacent areas. And a satellite analysis of more than 14,000 counties in that country reveals that areas located within a 10-minute walk of a park with sufficient trees have average temperatures 6 degrees Fahrenheit (3.3 degrees Celsius) lower than those further away.

In other words, vegetation cools cities. The shade of trees can reduce surface temperatures by up to 45 degrees Fahrenheit (25 degrees Celsius) in the most extreme cases, according to the United States Environmental Protection Agency. Added to this is the effect of evapotranspiration—the process by which water evaporates from the soil and is released by plants into the atmosphere—which further contributes to lowering the ambient temperature.