Lisbon records highs of 58.3°C on asphalt pavement in sun

A pilot campaign to measure the temperature of urban surfaces in Lisbon, coordinated by a residents’ association, recorded maximum temperatures of 58.3 degrees Celsius (°C) on asphalt pavement in the sun, corresponding to 31°C above the air temperature at the time.

This data comes from the TemperaturasLx project, coordinated by the residents’ association Vizinhos em Lisboa, which measured the temperature of urban surfaces in nine of the capital’s 24 parishes between June 12 and 17 – at times when the atmospheric temperature was around 21°C and 27°C, obtaining 245 readings in 108 locations.

With the aim of “identifying the most critical heat points”, creating a map of Lisbon’s heat islands, this pilot measurement campaign “found maximum temperatures of 58.3°C on asphalt pavement in the sun, up to 20°C higher than on Portuguese calçada (cobblestones) in the shade – where maximum values ​​of approximately 30°C were recorded.

In a statement, the association Vizinhos em Lisboa (Neighbors in Lisbon) argued that these results point to priority interventions such as “tree planting, shade, and water points,” to be proposed to parish councils and the wider City Council.

“On warmer days, which in the current context of climate change is becoming increasingly frequent, the surface values ​​recorded here will be even higher,” they emphasise.

While a maximum temperature of 58.3°C was recorded on asphalt pavement in the sun – which corresponded to 31°C above the air temperature at the time – measurements showed that the water in a fountain was at 23°C, 4°C below the atmospheric temperature.

Other data shows that maximum temperatures of approximately 41°C were recorded on Portuguese pavement in the sun, 30°C on Portuguese pavement in the shade, 34°C on lawn in the sun, and 26°C on lawn in the shade.

“These data demonstrate that shade, more than any other factor, is the public policy instrument with the greatest immediate return in terms of urban health,” argues the association.

The nine parishes where measurements were taken are Alvalade, Areeiro, Arroios, Avenidas Novas, Campo de Ourique, Estrela, Misericórdia, Santa Maria Maior and Santo António – with the campaign expected to be extended to the remaining 15 parishes of Lisbon during the summer, with volunteers, schools and local community groups.

The measurements were carried out with a portable infrared thermometer, which measures the radiation temperature of solid and liquid surfaces, the association explains, noting that the equipment used is not certified and is for indicative use, to “identify patterns and trends, support requests for technical inspections and guide intervention proposals”.

Among the nine parishes evaluated, Santo António, Misericórdia and Campo de Ourique have the highest average temperatures, exceeding 40°C.

The location with the highest average temperature in the entire sample is Avenida Álvares Cabral (Campo de Ourique), with 52.4°C in the sun, and the absolute maximum was recorded on Avenida Almirante Reis (Areeiro) with 58.3°C on bituminous pavement in a traffic lane.

Based on the data, Vizinhos em Lisboa highlight that Portuguese pavement in the shade is on average 10.2°C cooler than in the sun, noting that “a single tree with an adequate canopy produces this effect without any energy maintenance cost” and that grass in the shade registers temperatures lower than the air temperature, “behaving as an active cooling element through evapotranspiration”.

“The temperature difference between a bench in the sun and a bench in the shade is 15.9°C, greater than the difference between asphalt in the sun and pavement in the sun. Shading street furniture is as important as shading the pavement,” the association stresses, adding that the water in fountains and lakes recorded average temperatures of 22.9°C, much lower than any paved surface, arguing that “maintaining and expanding drinking fountains and water points is a measure with immediate impact.”

It goes without saying that these readings will hopefully dissuade dog owners from taking their pets out in the heat of the day.

One detail missing from the readings is how long pavements holding heat remain hot, once the sun is no longer shining on them.

Source material: LUSA