Strategies to keep major cities cool depend on location and precipitation. The urban heat island effect describes when city temperatures are much higher than in surrounding rural areas. Densely packed populations, asphalt roads, high-rise buildings, and traffic all contribute to the urban heat island effect.
The size and intensity of a city’s urban heat island depend largely on precipitation levels, which is why there is no simple solution to mitigating urban heat island effect.
The researchers designed a simple model that uses population and precipitation data. Summer temperature data from more than 30,000 cities worldwide were included in the framework.
“There are a few cities — New York, London, Baltimore — that are studied intensively, and we don’t know very much about a large range of other cities,” said Elie Bou-Zeid, an author of the study. “With a reduced model that only needs information on precipitation and population, we are hoping to provide a simple framework that can give guidance to any city.”
While high levels of rainfall are linked to rising city temperatures, this effect has its limits. For cities that get around 39 inches of rain each year, city temperatures do not increase much more than two degrees Fahrenheit.
The team found that wetter cities require different approaches to tackling urban heat island effect compared to drier regions. It has been suggested that planting more vegetation and creating ample green space can keep temperatures down, but in wetter cities planting more trees won’t reduce temperatures.
“In places that are already wet and vegetated, adding more vegetation is not going to help,” explained Bou-Zeid.
One the other hand, cities with drier climates like those in Arizona could benefit significantly from more vegetation.
The researchers will continue fine-tuning their model to include factors like how seasonal changes impact urban heat island.
“Our results show that there is no one-size-fits-all solution to reduce city-scale warming,” said Gabriele Manoli, the lead author of the study. “The efficiency of heat mitigation strategies varies across geographic regions, and any effort aimed at greening and cooling world cities should be put in the context of local hydro-climatic conditions.”
The researchers published their findings in the journal Nature.
Image Credit: Shutterstock/TWStock