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Ancient Japanese Water Ritual Cools Modern Cities
9 Oct
Summary
- Uchimizu tradition involves splashing water to reduce heat.
- Evaporation cools surfaces and surrounding air by drawing energy.
- Revival efforts underway in Japanese cities like Tokyo.
An ancient Japanese custom, known as uchimizu, is re-emerging as a potential strategy to combat rising urban temperatures. This practice, which involves splashing water onto the ground, leverages the principle of evaporative cooling to mitigate the effects of summer heat.
The tradition, documented as far back as the 17th century, sees water thrown across parched land, with its high heat of vaporization drawing heat away from surfaces and the air. Researchers have noted its revival efforts in cities such as Tokyo, with municipal programs sponsoring public events.
Scientific studies, including a 2018 Delft University of Technology research published in the journal Water, have quantified the cooling effects. Experiments demonstrated that uchimizu can cool the air by approximately 1.5 degrees Celsius. The cooling is more pronounced closer to the ground, especially on shaded pavement, with greater cooling observed when more water is applied.
While air conditioning led to a decline in the tradition over the past 50 years, there's a renewed interest in older, sustainable methods. Findings suggest that uchimizu is most effective on shaded surfaces and that the cooling effect persists as long as the ground remains wet, typically for over an hour.
Public trials, like those conducted in Tokyo since 2003, have shown average temperature reductions of around one degree Celsius. Despite the need for further study on city-wide impacts, uchimizu offers a simple, traditional solution for localized cooling.
