Verification of effects of heat measures

The Institute for Environmental Science has conducted joint research with the National Research and Development Agency Agency for Marine-Earth Science and Technology (JAMSTEC).
Among the joint research efforts with JAMSTEC, in addition to the actual measurement survey, in order to verify the effectiveness of heat countermeasures, we examined the effects of introducing heat countermeasures under virtual conditions (for example, setting partitions near mist) and changes in the heat environment when setting values that affect heat mitigation (for example, the density of tree leaves, etc.) were changed.
In this page, we will introduce an example of each approach.

What is the Heat Island phenomenon?　／　Heat Island countermeasures　／　Temperature Observation in the City　／　 Heat Environment Survey　／　 Future forecast of city temperature

Special pavements such as water-retaining pavements and permeable pavements have the function of reducing the heat by storing rainwater in the pavement and reducing the temperature (ground surface temperature) of the pavement surface by the vaporization heat of the retained water. I am.
These special pavements have been introduced in a part of Mudgame Park in Kanazawa Ward, Yokohama City, and the water retention rate of the special pavement at this location is arbitrarily set, and the difference in surface temperature due to changing the evaporation efficiency from the pavement surface was verified by numerical simulation.
As a result of the verification, in the location of water-retaining pavement and permeable pavement, the ground surface temperature when setting the water retention rate during drying is 2 to 8 ° C higher, and the ground surface temperature when setting the water retention rate during wetting is 4 to 8 ° C lower than the normal water retention rate.

In addition, it was found that the difference in the water retention rate of special pavement also affects the temperature close to the ground surface (0.5m high).
During drying, water vaporization from the ground surface is low, and heat is used to increase the ground surface temperature, resulting in warming the surrounding air. For this reason, compared to normal times, it increased by up to 0.3 to 0.4 ° C near the water-retaining pavement on the south side of the park.
On the other hand, during wetting, heat is used to evaporate moisture from the ground surface, making it difficult for the ground surface temperature to rise and weaken the effect of warming the surrounding air. For this reason, compared to normal times, it was possible to see a drop in temperature throughout the park, with a maximum of about 0.7 ° C lower near water-retaining pavements and permeable pavements.

In this way, it has become possible to estimate the effects of heat mitigation by utilizing simulation technology even for efforts that are difficult to verify in actual measurement surveys.
For details of this initiative, please see pages 10 to 15 (* 1) of the results report.

※１　Chapter 5-1 Verification of the effect of water retention and greening of ground surfaces, etc.

The mist has the effect of cooling the air by spraying a mist-like water droplet, which deprives heat when the water droplets evaporate.
In order to maintain the cooling effect of the mist higher, the effectiveness of suppressing the spread of mist by providing partitions on the downwind side was examined in the case of mist installed at Mudgame Park in Kanazawa-ku, Yokohama.
As a result of using simulation technology to predict changes in temperature and other factors when a partition is set up, it was found that by providing a mesh-shaped partition with permeability, the temperature drops inside the partition.
In addition, when we actually installed a temporary windbreak net under the wind of the mist in Deiki, Kanazawa-ku Park, we were able to confirm that the temperature etc. had dropped inside the partition in actual measurement surveys.

Based on the above, it is considered that it is effective to prevent the spread of mist, such as by providing a partition on the lower side, in order to enhance the effect of mist.
For details of this initiative, please see pages 16 to 26 (* 2) of the results report.

※２　Chapter 5-2 Verification of the effect of micromists

As of 2018, there are more than 130,000 street trees (sidewalk trees and other Takagi) in Yokohama City. Street trees have various roles, such as creating shades of greenery to block the hot summer sunshine, lowering the temperature by the transpiration of leaves, and purifying the air by breathing plants and adsorbing air pollutants to leaves. It has the effect of
In order to investigate the heat mitigation effect of the shade of street trees, we conducted an actual measurement survey on the sidewalk of the main road where street trees (zelkova) are planted from the vicinity of Torigaoka, Totsuka-ku, Yokohama City to the vicinity of Ryoke, Izumi-ku. . As a result, compared to the green shade of strong pruning (pruning down trunks and thick branches to reduce the tree shape), the green shade of soft pruning (pruning to maintain a certain size while utilizing the tree shape) Has confirmed that the heat environment has been eased.
Soft pruning has a darker greenness in the Kimata body, and the branches and leaves block sunlight more, so it has a greater heat mitigation effect, and it forms a large shade of green, so it is expected to feel cool. It is thought that the area (range) has increased.

In addition, we modeled the street trees that were surveyed and verified them using numerical simulations.
In numerical simulations, in order to examine the elements of the role of street trees that affect the coolness of the shade of green, the height of the trees, the crown volume (6 types (*3) from Case 1 to 6), and the density of leaves (6 types of Case 7 to 12 (*3)), how the heat index (WBGT) changed.
As a result, the heat index in the shade of green depends on the solar radiation intensity that reaches the ground surface, and the greater the density of the leaves or the larger the canopy volume, the lower the heat index and the less the heat felt by humans. I found that the greater the effect.

※３　Canopy parameters used in Case 1 to 12 (PDF: 390KB)

In addition, based on the results obtained from numerical simulations, the conceptual diagram shows the relationship between the canopy characteristics (the density of leaves and the volume of the canopy) and the heat index.
If the density of the leaves has to be reduced, increase the crown volume (enlarge the value of the horizontal axis), and if the crown volume cannot be increased, increase the density of the leaves (enlarge the vertical axis) It was found that increasing the value of the vertical axis) can reduce the heat index, that is, improve the heat environment.

For details on the initiatives, please see pages 27 to 43 (* 4) of the results report.

※４　Chapter 5-3 Verification of differences in heat environment due to differences in pruning methods for street trees