How cool is uchimizu?
It has long been known
that cities are hotter than the surrounding countryside. Roads and buildings
absorb and retain more heat than soil and vegetation. For centuries the
technique of uchimizu has been used
in Japan to cool down that urban heat: uchimizu
is the simple old Japanese tradition of water sprinkling. That uchimizu indeed is an effective way of
reducing extreme heat in cities – it also works well against dust by the way -
has been shown by Delft researcher Anna Solcerova and colleagues. She presented her work at the 2017 EGU
General Assembly (European Geosciences Union).
Presentation Anna Solcerova (from 16 minutes)
Presentation Anna Solcerova (from 16 minutes)
Urban Heat Island
It has long been
known that, generally speaking, cities are hotter than the surrounding
countryside; a phenomenon known as the ‘Urban Heat Island’ (UHI). Roads and
buildings absorb and retain more solar radiation than the soil and vegetation
found more prominently in the countryside. This causes the city to heat up
more, an effect which is further reinforced by human activity such as heating
and transport.
17th century
The Urban Heat Island
effect was first described some 200 years ago, but methods for mitigating heat
in urban areas have been around much longer. ‘Uchimizu is one of these techniques, which was already being used
in Japan in the 17th century’, says Anna Solcerova. Houses, temples and gardens
and their surroundings were sprinkled with water to cool the surfaces and the
air, and to keep down the dust. Nowadays, mega-cities such as Tokyo are
attempting to breathe new life into these old methods. Local authorities
promote uchimizu as a “smart way to
stay cool”. ‘I was unable to find much in scientific literature about the
effect of uchimizu. The number of
studies published that quantify the cooling effect is limited, and they only
use temperature measurements from a certain height above ground.’
Cooling
Solcerova and Van Emmerik carried out several
experiments to systematically study the effect of the amount of water, the
starting temperature of the surface and the influence of shade on the cooling
effect of uchimizu. During the
conference in Vienna, the researchers will present the results and analysis of
the experiments which were carried out during one summer in Delft. The general
conclusion is that uchimizu always
works; the ground always becomes cooler. But the effect is greatest at times
when the heat is less intense. And the effect in the shade is greater than in
the sun (due to evaporation). ‘We show that this simple method of sprinkling
water has the potential to considerably reduce extreme heat in paved urban
areas. In addition, uchimizu presents
an opportunity to increase the awareness of city dwellers and to encourage them
to solve heat stress and to save energy. By adding new insights to the existing
knowledge of uchimizu, we want to
contribute to a revival of this old tradition.’
More information
Besides the presentation ‘How cool is uchimizu?’ at the EGU General Assembly in Vienna on April 26, an article will be submitted in the Journal of Applied Meteorology and Climatology.
Anna Solcerova: https://www.tudelft.nl/staff/a.solcerova
Presentation Anna Solcerova (from 16 minutes)
Anna Solcerova: https://www.tudelft.nl/staff/a.solcerova
Presentation Anna Solcerova (from 16 minutes)
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