Traditional Japanese uchimizu technique works to cool down hot cities

April 24, 2017, Delft University of Technology
Credit: Delft University of Technology

The simple old Japanese tradition of water sprinkling - uchimizu - is an effective way of reducing extreme heat in cities. This will be TU Delft researcher Anna Solcerova's message at the EGU General Assembly (European Geosciences Union) in Vienna on Monday 24 April.

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 have been around much longer. 'Uchimizu is one of these techniques, which was already being used in Japan in the ', 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.'


For this reason, this study, which is part of Anna Solcerova's PhD research, uses a 3-D Distributed Temperature Sensing (DTS) system to record extremely precisely (in space and time) the air temperature in one specific cubic metre of air above a pavement in a city. Solcerova and her colleague Tim van Emmerik tested this system using a large cube with fibre optic cables (designed by Van Emmerik and TU Delft colleague Koen Hilgersom) that measure the temperature. They poured water around and under the cube; first 1 mm, then 2 mm, and so on.


Several experiments were carried out 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 in paved urban areas. In addition, uchimizu presents an opportunity to increase the awareness of city dwellers and to encourage them to solve 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.'

Explore further: Researchers plant seeds to make renewable energy more efficient

Related Stories

When the heat is on, we need city-wide plans to keep cool

January 30, 2017

The recent spate of heatwaves through eastern Australia has reminded us we're in an Australian summer. On top of another record hot year globally, and as heatwaves become more frequent and intense, our cities are making ...

Using Google to map our ecosystem

February 28, 2017

Researchers in the Singapore-ETH Centre's Future Cities Laboratory developed a method to quantify ecosystem services of street trees. Using nearly 100,000 images from Google Street View, the study helps further understanding ...

Cool roofs in China offer enhanced benefits during heat waves

December 22, 2015

It is well established that white roofs can help mitigate the urban heat island effect, reflecting the sun's energy back into space and reducing a city's temperature under normal weather conditions. In a new study of Guangzhou, ...

Recommended for you

Light-based production of drug-discovery molecules

February 18, 2019

Photoelectrochemical (PEC) cells are widely studied for the conversion of solar energy into chemical fuels. They use photocathodes and photoanodes to "split" water into hydrogen and oxygen respectively. PEC cells can work ...

Solid-state catalysis: Fluctuations clear the way

February 18, 2019

The use of efficient catalytic agents is what makes many technical procedures feasible in the first place. Indeed, synthesis of more than 80 percent of the products generated in the chemical industry requires the input of ...

Engineered metasurfaces reflect waves in unusual directions

February 18, 2019

In our daily lives, we can find many examples of manipulation of reflected waves, such as mirrors, or reflective surfaces for sound that improve auditorium acoustics. When a wave impinges on a reflective surface with a certain ...

Design principles for peroxidase-mimicking nanozymes

February 18, 2019

Nanozymes, enzyme-like catalytic nanomaterials, are considered to be the next generation of enzyme mimics because they not only overcome natural enzymes' intrinsic limitations, but also possess unique properties in comparison ...

Sound waves let quantum systems 'talk' to one another

February 18, 2019

Researchers at the University of Chicago and Argonne National Laboratory have invented an innovative way for different types of quantum technology to "talk" to each other using sound. The study, published Feb. 11 in Nature ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Apr 30, 2017
Hottest on record in a city of 5 million people. Comparing this Hottest on record temp to temperatures in the same location 150 years ago is pointless because of the Urban Heat Island effect..
100 km away from this heat island, temps drop about 10 degrees...
So much for CO2?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.