Uchimizu: A Cool(ing) Tradition to Locally Decrease Air Temperature

Abstract

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.

Governing the Urban Climate in Fukuoka City, Japan: What Can a Policy Narrative Approach Teach Us?

“…Fukuoka City Government held an uchimizu event in summer 2019 with the explicit purpose of raising awareness of the urban heat island effect (Fukuoka City 2019a); and Fukuoka Prefectural Government provide technical data on how a community uchimizu event reduced surface temperature from 51 to 46.1 on a hot summer day (Fukuoka Prefecture 2019). However, uchimizu as a practice to promote cooling in Japan dates back to the seventeenth Century (Solcerova et al 2018), illustrating that the idea of creating and sustaining a comfortable environment extends far beyond the 'official' and techno-scientific justifications for uchimizu offered in more recent times.…”

Present day and future urban cooling enabled by integrated water management

“…The use of water provides urban cooling through evaporative cooling from large water bodies (Theeuwes et al, 2013;Völker et al, 2013). Additionally, irrigation of vegetated surfaces (Broadbent et al, 2017;Cheung et al, 2021) as well as impervious surfaces (Hendel et al, 2016;Solcerova et al, 2018) can provide cooling benefits.…”