Cities are hotter than ever. Here are 5 things they can do about it

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A healthy canopy of trees is among the most effective and egalitarian defenses against the urban heat island effect. Seeking refuge beneath a tree can feel 11 to 25 degrees Celsius (20 to 45 degrees Fahrenheit) cooler compared to standing in direct sunlight, according to the US Environmental Protection Agency. Apart from the instant relief of shade, a process called “evapotranspiration,” where water transfers from plants and soil into the atmosphere, also helps cool surrounding areas by up to 5 degrees Celsius (9 degrees Fahrenheit).

Barcelona, which has become something of a laboratory for progressive urban interventions, may soon offer a vital case study on the efficacy of trees. Per its “Tree Master Plan,” the Spanish city aims to blanket 30% of its land with a variety of climate-resilient species by 2037. Today, holm oaks, Aleppo pines, plane trees, cypresses and other hardy species already line the city’s streets and new “superilla,” or superblocks, which are essentially reclaimed roads that have been turned into tree-lined public plazas. Only a handful of the planned 503 superblocks were completed in time for this grueling Spanish summer, though the city plans to finish them all by the end of the decade.