An old Japanese tradition of sprinkling water on the ground can reduce the urban heat island effect by up to 8 degrees Celsius. Authorities are now trying to revive the technique as a ‘smart way to stay cool’.
The Japanese developed a water sprinkling technique called uchimizu in the 17th century to reduce heat in urban areas. Water was poured around houses, temples and gardens to settle the dust and cool the surfaces and the air.
As Anna Solcerova, a researcher at Delft University of Technology, told participants at the General Assembly of the European Geosciences Union in Vienna on Monday, local authorities in mega-cities like Tokyo are trying to revive this traditional method in the face of rising urban temperatures.
As part of her PhD research, she set out to determine the precise cooling effect of uchimizu using a 3D Distributed Temperature Sensing (DTS) system that records air temperature in one specific cube metre of air. With 53 horizontal levels and more than 35,000 measurement points, the cube produces very precise measurements in time and space.
Her experiments revealed that uchimizu has a cooling effect of up to 8 degrees Celsius, with the greatest cooling at ground level as that is where the water is poured. But it can still cool the air by up to 2 degrees Celsius at 1.5 to 2 metres above the ground, or the height of an average person.
Uchimizu has the big advantage that it promotes citizen participation as anyone can pour water onto pavement without requiring permission from the authorities, says Solcerova. It also increases the awareness of city dwellers and encourages them to solve heat stress and save energy. Finally, it can be used anywhere in the world where rainwater is easily harvested.