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- Lau, Kevin Ka-Lun, 1983, et al.
(författare)
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Street geometry design and its effect on mean radiant temperature: A parametric study based on numerical modelling
- 2015
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Ingår i: ICUC9 – 9 th International Conference on Urban Climate jointly with 12th Symposium on the Urban Environment. 20-24 July 2015, Toulouse, France.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The spatial variation of hotspots, in terms of their locations and magnitude, is examined in the present study, using the Solar and LongWave Environmental Irradiance Geometry (SOLWEIG) model. The effect of street geometry design parameters such as H/W ratios and street orientations on the radiant heat load are analyzed for three European cities with different regional climatic conditions. Various physical configurations of street trees are examined for their corresponding potential in mitigating the radiant heat load within urban structures. Findings suggest that a dense urban structure (H/W ratio ≥ 2) is capable of reducing radiant heat load at street level. High H/W ratios do not only reduce the magnitude of hotspots, but also changes their spatial distribution. The N-S canyons are found to be more favourable than the E-W canyons since they limit sun exposure to several hours at noon, despite of the diminishing difference between two orientations when H/W ratio increases. Diagonal streets reduce the magnitude of hotspots but increase the areas affected by moderately high mean radiant temperature (Tmrt). NE-SW orientated streets exhibits higher average hourly Tmrt during daytime since they are largely sun-exposed at the hottest time of the day. The highest mitigating effect of street trees is found when they are located in the sunlit areas. The reduction in average Tmrt decreases with increasing H/W ratios but considerable mitigating effect is still observed in the NE-SW orientations. It is also observed that larger tree crowns, even with higher spacing between individual trees, provide better shading than closely placed trees with smaller tree crowns. The present study provides information about the locations and magnitude of hotspots in different urban settings as well as the design of street trees as a mitigation measure to radiant heat load. It helps urban planners and designers to better design neighbourhoods in order to improve pedestrian thermal comfort within urban areas.
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| 3. |
- Lau, Kevin Ka-Lun, 1983, et al.
(författare)
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The effect of urban geometry on mean radiant temperature under future climate change: a study of three European cities
- 2015
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Ingår i: International journal of biometeorology. - : Springer Science and Business Media LLC. - 0020-7128 .- 1432-1254. ; 59:7, s. 799-814
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Tidskriftsartikel (refereegranskat)abstract
- Future anthropogenic climate change is likely to increase the air temperature (T a ) across Europe and increase the frequency, duration and magnitude of severe heat stress events. Heat stress events are generally associated with clear-sky conditions and high T a , which give rise to high radiant heat load, i.e. mean radiant temperature (T mrt ). In urban environments, T mrt is strongly influenced by urban geometry. The present study examines the effect of urban geometry on daytime heat stress in three European cities (Gothenburg in Sweden, Frankfurt in Germany and Porto in Portugal) under present and future climates, using T mrt as an indicator of heat stress. It is found that severe heat stress occurs in all three cities. Similar maximum daytime T mrt is found in open areas in all three cities despite of the latitudinal differences in average daytime T mrt . In contrast, dense urban structures like narrow street canyons are able to mitigate heat stress in the summer, without causing substantial changes in T mrt in the winter. Although the T mrt averages are similar for the north–south and east–west street canyons in each city, the number of hours when T mrt exceeds the threshold values of 55.5 and 59.4 °C—used as indicators of moderate and severe heat stress—in the north–south canyons is much higher than that in the east–west canyons. Using statistically downscaled data from a regional climate model, it is found that the study sites were generally warmer in the future scenario, especially Porto, which would further exacerbate heat stress in urban areas. However, a decrease in solar radiation in Gothenburg and Frankfurt reduces T mrt in the spring, while the reduction in T mrt is somewhat offset by increasing T a in other seasons. It suggests that changes in the T mrt under the future scenario are dominated by variations in T a . Nonetheless, the intra-urban differences remain relatively stable in the future. These findings suggest that dense urban structure can reduce daytime heat stress since it reduces the number of hours of high T mrt in the summer and does not cause substantial changes in average and minimum T mrt in the winter. In dense urban settings, a more diverse urban thermal environment is also preferred to compensate for reduced solar access in the winter. The extent to which the urban geometry can be optimized for the future climate is also influenced by local urban characteristics.
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