ROADS that trap water like a baby’s nappy could help keep the sweltering
streets of Tokyo cool, say the city’s engineers.
In the countryside, the air is cooled by water evaporating from leaves and
soil, and the vegetation also provides shade, keeping down temperatures. But
like many cities, built-up Tokyo doesn’t have much vegetation and as a result
suffers from the “urban heat island” effect.
In July, the city can be a few degrees hotter than the surrounding
countryside—often exceeding 30 °C. The materials used to build roofs,
roads and pavements compound the effect by absorbing more of the…
