Study: Trees can reduce mortality during heat waves in cities. Even by a third

Cities tend to experience warmer temperatures than surrounding suburbs or rural areas. This is the so-called the urban heat island effect, caused primarily by the lack of vegetation and the presence of dark asphalt roads that absorb huge amounts of heat.

This is exacerbated by climate change, which made last summer in Europe the hottest on record. Published in The Lancet, the study focuses on how to combat urban heat with vegetation.

Researchers from Spain, Italy, the UK and the US analyzed premature mortality rates in 93 European cities. Scientists were interested in cases from the summer of 2015, which concerned people over 20 years old. The data was analyzed in relation to daily average temperatures for this period.

On average, in the summer of 2015, the temperature in cities was 1.5 degrees Celsius higher than in the surrounding countryside. The city with the biggest difference, as much as 4.1 degrees Celsius, was Cluj-Napoca in Romania. Across all urban centers, 75 percent of the population lived in areas that were at least one degree warmer than the surrounding countryside, and 20 percent experienced temperatures two degrees warmer.

Of all the deaths, as many as 6,700 may have been directly caused by the urban heat island effect on the body. The cities with the highest rates of temperature-related mortality were in southern and eastern Europe.

Based on the collected data, the researchers also calculated what these statistics would look like if the share of wooded areas in cities was increased to 30 percent – currently this indicator is 14.9 percent on average. The model showed that the denser vegetation cover could have reduced the number of heat deaths by up to 2,644 cases, or more than a third. The introduction of more trees into the urban landscape would also reduce the temperature on hot summer days by about 0.4 degrees Celsius.

As lead author of the study Tamara Iungman from the Barcelona Institute for Global Health explains, high temperatures in cities are associated with serious health consequences, including cardio-respiratory failure.

– Our goal is to inform politicians and decision-makers about the benefits of including green areas in spatial planning processes – he explains. ‘This is important as Europe is experiencing increasingly extreme temperature fluctuations due to climate change.

Previous research has shown that green spaces can have additional health benefits for city dwellers. Introducing trees and shrubs has a positive effect on mental health and cognitive abilities in children and the elderly.