Trees and heat islands

Rox Pena
Rox Pena

With the unbearable hot weather, many are appreciating the benefits that trees provide to the environment. Trees lower surface and air temperatures by providing shade and cooling through evaporation and transpiration, also called evapotranspiration. They reduce runoff and improve water quality by absorbing and filtering rainwater. To get a feel of the cool atmosphere provided by trees in an urban setting, visit the house of my radio partner Cecile Yumul in Lakandula, Mabalacat City.

Nowadays, trees are cut to give way to road widening, subdivision, industrial and commercial developments. It’s not just their loss that is contributing to this very hot weather. The hot temperature is amplified by the urban heat island effect, a situation where urbanized areas experience higher temperatures than outlying areas. When surfaces are cemented or covered with buildings, the change in ground cover results in less shade and moisture to keep urban areas cool. Paved areas also evaporate less water, which contributes to higher surface and air temperatures.

Structures such as buildings, roads, and other infrastructure absorb and re-emit the sun’s heat more than natural landscapes such as forests and water bodies. Nighttime temperatures in heat islands are high because cemented areas block heat coming from the ground from rising into the cold night sky. Because the heat is trapped on lower levels, the temperature is warmer.

Heat islands can worsen the impact of naturally occurring heat waves like what we are experiencing now. Warm summer months are hotter today due to climate change. The weather was made even hotter by the El Niño phenomenon resulting in record hot temperatures from June 2023 to March 2024.

Heat islands contribute to heat-related deaths and heat-related illnesses such as general discomfort, respiratory difficulties, heat cramps, heat exhaustion, and non-fatal heat stroke. A study published in The Lancet and led by the Barcelona Institute for Global Health (ISGlobal), revealed that over four percent of deaths in cities during the summer months are due to urban heat islands. The study results were obtained with data from 93 European cities.

One simple way to mitigate the heat island effect is to plant trees and other vegetation. Space in urban areas might be limited, but trees can be planted in grassy or barren areas, vacant lots, and open spaces. According to the ISGlobal study, one third of the deaths could have been prevented by increasing tree cover up to 30%, thereby reducing temperatures.

On the long term, good urban planning with the right blend of greeneries, open spaces and mixed-use areas will minimize heat islands. For existing areas, green roofs, also called ‘vegetated roofs’ or ‘living roofs,’ will help provide direct and ambient cooling effects. Vertical gardens on tall structures may also provide relief from heat.

We are saddened by the loss of trees, but we should be upset too by the lack of initiative to plant them. In spite of a law that requires us to plant at least one tree every year, there seems to be no significant progress in re-greening our land. Let’s plant trees now.

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