Abstract
The urban heat island effect was first described 200 years ago, but the development of ways to mitigate heat in urban areas reaches much further into the past. Uchimizu is a 17th century Japanese tradition, in which water is sprinkled around houses to cool the ground surface and air by evaporation. Unfortunately, the number of published studies that have quantified the cooling effects of uchimizu are limited and only use surface temperature or air temperature at a single height as a measure of the cooling effect. In this research, a dense three-dimensional Distributed Temperature Sensing (DTS) setup was used to measure air temperature with high spatial and temporal resolution within one cubic meter of air above an urban surface. Six experiments were performed to systematically study the effects of (1) the amount of applied water; (2) the initial surface temperature; and (3) shading on the cooling effect of uchimizu. The measurements showed a decrease in air temperature of up to 1.5 °C at a height of 2 m, and up to 6 °C for near-ground temperature. The strongest cooling was measured in the shade experiment. For water applied in quantities of 1 mm and 2 mm, there was no clear difference in cooling effect, but after application of a large amount of water (>5 mm), the strong near-ground cooling effect was approximately twice as high as when only 1 mm of water was applied. The dense measurement grid used in this research also enabled us to detect the rising turbulent eddies created by the heated surface.
Highlights
In the past, the Japanese water throwing tradition known as uchimizu has been used widely to cool urban surfaces and decrease the air temperature around houses and in gardens
This paper presents and analyzes measurements of six experiments, with varying initial air temperature, ground surface temperature, shading, and applied amount of water
Slingerland (2012) [26] showed that a high amount of water might have a larger influence than 1 mm of water on the near ground temperatures, which suggests that Experiment 6 might result in different vertical cooling profile than the other experiments
Summary
The Japanese water throwing tradition known as uchimizu has been used widely to cool urban surfaces and decrease the air temperature around houses and in gardens. Uchimizu (combination of uchi for hit or throw, and mizu for water) is a tradition that stems from the 17th century [1]. Over the last 50 years, this environmental control method has lost popularity. This has been mainly caused by a rapid development in technology and by socio-economic change, causing citizens to feel that traditional methods were too laborious or low class [2]. Citizens practicing uchimizu in Japanese urban areas have been found to use less air-conditioning, which significantly decreases their domestic energy consumption [2]. It was found that the level of outdoor comfort among citizens is higher in areas that applied uchimizu [3]
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