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Ancient Japanese technique becomes cool again

by Liz Kalaugher

The 17th century saw Japanese citizens sprinkle water onto the ground and walls around their temples, gardens and houses. Not only did this suppress dust formation but it also cooled temperatures by evaporation. Now Tokyo is promoting uchimizu once more and a team from the Netherlands has investigated exactly how much this uchimizu technique could benefit today’s cities.

As Anna Solcerova of the Delft University of Technology in The Netherlands detailed at the European Geosciences Union (EGU) meeting in Vienna, adding just 1 or 2 mm of water to a paved area can reduce air temperatures near the ground by as much as 8-10 degrees and at human height by up to 2 degrees.

To come up with these figures, Solcerova and colleagues Tim van Emmerik and Koen Hilgersom fitted a 1 x 1 x 1 m cube with fibreoptic temperature sensors, providing 3D Distributed Temperature Sensing (DTS) measurements at 35 heights.

Adding water always cools the ground, the team found, but the effect is greater when the heat is less intense, or in shade. Solcerova stressed that it’s important to use rainwater rather than tap water for uchimizu and that the technique boosts humidity – whilst this would not be an issue in the Netherlands, it may be elsewhere.

The uchimizu technique died out with the advent of aircon units that can cool a room to any temperature desired, although on the downside, the units spew additional heat into the city outside. Perhaps we’ll see more of uchimizu in the future.

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