Nature on our doorsteps: Trees, helping to keep us cool . . .

Rosaleen Dwyer is the County Heritage Officer at South Dublin County Council – every week she gives us an insight into the natural heritage around us and the beautiful biodiversity of the plants and creatures.

TREES offer a number of different important benefits to us, particularly in the built-up areas of our villages, towns, and cities.

While trees are recognised as important habitats for insects, birds, bats, and squirrels, a less visible benefit of trees in the urban environment would have been operating during the recent heatwave conditions.

Hot weather is more uncomfortable in our towns and cities than it is in the open countryside.

This is due to something called the ‘urban heat island’ effect. This effect results from the abundance of bricks and concrete used to construct walls and buildings, and from the many kilometres of asphalt laid down in roads and streets.

In sunny weather, these construction materials warm up quickly during the day.

They can then bounce, or radiate, this absorbed heat back into the air around us, adding even more heat to the air in the urban environment.

These construction materials also take time to cool down every evening.

These trees are helping to reduce the heat absorbed by road asphalt and concrete

They can continue to radiate heat back at us, long after sunset. In heatwave conditions, night-time therefore offers little respite from the  heat.

Trees, however, can significantly help by keeping the air around us cool.

A tree’s canopy acts like a parasol. It can directly shade external walls and windows, preventing up to  95 per cent of the sun’s rays reaching buildings and the ground.

This welcome shade helps to keep things cool. It also reduces how much heat is absorbed and radiated back at us by asphalt, bricks, and concrete.

Large mature trees are more effective at doing this than smaller trees.

Another way trees help is by a process called evapo-transpiration. When the sun shines on a tree, water is evaporated from its leaves, adding moisture directly into the air.

When the weather is hot and dry, the cool moist air around trees is more comfortable for us to breathe.

In other countries where summers are generally hotter than in Ireland, trees are deliberately planted throughout towns and cities to help make living in urban areas more comfortable.