Urban design and thermal comfort outdoors in warm-humid climates

Aims and method:

Investigates the relationship between urban design, urban microclimate, and outdoor comfort across different street patterns and in low-, medium-, and high-rise buildings in Dar es Salaam, Tanzania. Air temperature, wind speed, mean radiant temperature, and the physiologically equivalent temperature are simulated using ENVI-met to highlight the strengths and weaknesses of the existing urban design.

Key findings:

· Areas with low-rise buildings suffer from greater heat stress in urban spaces than areas with high-rise buildings.

· The use of dense trees helps to enhance the thermal comfort conditions by reducing reduce heat stress.

· Provision of shade is a more efficient way to reduce physiologically equivalent temperature than increases in wind speed.

Reference:

Yahia, M. W., Johansson, E., Thorsson, S., Lindberg, F., & Rasmussen, M. I. (2017). Effect of urban design on microclimate and thermal comfort outdoors in warm-humid Dar es Salaam, Tanzania. International Journal of Biometeorology, 1-13.

https://link.springer.com/article/10.1007/s00484-017-1380-7

The cooling and energy saving effect of landscape

Aims and method:

Investigates the cooling and energy saving effect of landscape parameters in an urban park of Beijing during a hot summer. Continuous on site microclimate data of the impact of individual parameters including grass, water bodies, trees and artificial shading devices and different combinations were collected. The thermal perception of people as effected by each parameter was studied according to both the measured data and thermal sensation votes from a questionnaire survey.

Key findings:

· Whilst it is possible to build manmade shading devices to deliver optimum cooling and energy saving effects, natural elements such as grass, trees and water can have similar impacts.

· Optimal benefits can be obtained by a combination of manmade and natural elements, notably designed shading and trees

Reference:

Xu, X., Sun, S., Liu, W., García, E. H., He, L., Cai, Q., & Zhu, J. (2017). The cooling and energy saving effect of landscape design parameters of urban park in summer: A case of Beijing, China. Energy and Buildings.

http://www.sciencedirect.com/science/article/pii/S0378778816319764

Energy, cool surfaces and shade trees

Aims and method:

Explores the relation between the existence of trees and other non-absorbent surfaces in urban areas and the energy demand for cooling and associated impacts on pollution in American cities. A range of simulation models were used to simulate energy use against different three dimensional ground conditions.

Key findings:

· Cool surfaces (cool roofs and cool pavements) and urban trees can have a substantial effect on urban air temperature and, hence, can reduce cooling-energy use and smog.

· About 20% of the national (USA) cooling demand can be avoided through a large-scale implementation of heat-island mitigation measures, with major impacts on liveability through reducing smog and urban heat island effects

· This amounts to 40 TWh/year savings, worth over $4 billion per year by 2015, in cooling-electricity savings alone. Once the benefits of smog reduction are accounted for, the total savings could add up to over $10 billion per year (2001 prices).

Reference:

Akbari, H., Pomerantz, M., & Taha, H. (2001) Cool surfaces and shade trees to reduce energy use and improve air quality in urban areas, Solar Energy, 70(3), 295-310

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.155.1477&rep=rep1&type=pdf

Urban form and reducing energy load through cooling

Aims and method:

Develops and tests a statistical model for estimating space-cooling energy use in residential homes by incorporating variables that represent external built form in the US. The study integrates a variety of quantitative data including geographic information systems (GIS) and light detecting and ranging data (LiDAR) to extract high resolution variables to represent urban form. These are combined with occupant behaviour, property and sociodemographic data to form 2D and 3D spatial data.

Key Findings:

· Higher population density, east-west street orientation, higher green space density within 100 ft radius, and a higher sum of tree heights on the east, south and west side of houses have statistically significant effects on summer cooling energy consumption.

· Building at greater density; planting more trees and greenspace at community level; and east-west street orientation, can all reduce energy load through cooling.

Reference:

Ko, Y., & Radke, J. D. (2014). The effect of urban form and residential cooling energy use in Sacramento, California. Environment and planning B: Planning and Design, 41(4), 573-593.

http://journals.sagepub.com/doi/abs/10.1068/b12038p

Pollution and resident behaviours

Aims and method:

Examines the impacts of traffic noise, air pollution and lack of public green space on self-reported health and well-being of Berlin residents. The study combines quantitative measures including a combination of GIS mapping of the environmental indicators and a survey of residents to analyse the relations between multiple neighbourhood burdens and health indicators, incorporating both ambient stressors and lack of environmental resources.

Key Findings:

· Traffic noise is the only statistically significant relationship with self-reported health behaviour

· Approximately a third of the variation in neighbourhood satisfaction scores was explained by the levels of traffic noise, air pollution and availability of green space.

· Perceived air pollution has the biggest impact on health behaviours.

Reference:

Honold, J., Beyer, R., Lakes, T., & van der Meer, E. (2012). Multiple environmental burdens and neighborhood-related health of city residents. Journal of Environmental Psychology, 32(4), 305-317.

http://www.sciencedirect.com/science/article/pii/S027249441200028X

Community noise exposure and stress in children

Aims and method:

Examines the stress outcomes of typical, everyday community noise exposure among children. The work examined multi-methodological indices of stress among young children living under 50 dB or above 60 dB in small towns in Austria.

Key findings:

· Children living in relatively noisy neighbourhoods had raised blood pressure, heart rates and levels of stress hormones, effects that happen at noise levels far below those required to damage hearing.

· Increased background noise also seemed to reduce child motivation, especially amongst girls and to ‘learned helplessness’ syndrome.

Reference:

Shield, B. M., & Dockrell, J. E. (2003). The effects of noise on children at school: a review. Building Acoustics, 10(2), 97-116.

http://journals.sagepub.com/doi/abs/10.1260/135101003768965960

Influence of density and morphology on urban heat island intensity

Aims and method:

The research simulated the urban climate of various generated cities under the same weather conditions. For mono-centric cities, a linear combination of logarithmic city area and logarithmic gross building volume was proposed, which also captured the influence of building density. By studying various city shapes, a reduced form to estimate urban heat island intensities based only on the structure of urban sites as well as their relative distances was generalised and proposed

Key findings:

·      Given the same urban area or gross building volume, the UHI intensity is strongly influenced by the building density so that increasing building density will lead to stronger urban heat island intensity. 

·      Due to different effects of aspect ratio, increasing building plan area causes a more rapid increase in urban heat island intensity than adding vertical building height.

·      There is an amplifying effect that neighbouring sites have on each other.

Reference:

Li, Y., Schubert, S., Kropp, J. P., & Rybski, D. (2020). On the influence of density and morphology on the Urban Heat Island intensity. Nature Communications, 11(1), Article 2647.

https://doi.org/10.1038/s41467-020-16461-9

Association between urban form and air quality

Aims and method:

The study aims to evaluate the association between urban form and air quality in China through the use of empirical evidence. The relationship between a variety of urban form metrics and concentrations of air pollutants were analysed through linear regressions using a data set of cross-sectional observations from 157 Chinese cities.

Key findings:

·      Higher population density and lower urban continuity are commonly associated with better air quality

·      Urban continuity has a significant but opposing influence on air quality for higher density Chinese cities than it does in lower density American and European cities

·      Urban form could play a modest but important role in improving air quality for Chinese cities.

Reference:

Yuan, M., Song, Y., Huang, Y., Hong, S., & Huang, L. (2018). Exploring the Association between Urban Form and Air Quality in China. Journal of Planning Education and Research, 38(4), 413–426. 

https://doi.org/10.1177/0739456X17711516

Green perimeter and the thermal environment around buildings

Aims and method:

The study analysed the impact of the location and type of green perimeter (green median or belt) around buildings on the thermal environment next to buildings. A co-benefit assessment model was developed to quantify green belt design parameters based on the identification of optimal green belt types and locations.

Key findings:

·      Compared with buildings without green perimeters, the optimal design (i.e. lawns, shrubs and trees configuration) could decrease the temperature around the building by 1.85°C, while the cooling efficiency reached 47.20%. 

·      The optimal lawn area distance was determined to be 0.5 S (S is the building’s footprint), the optimal shrub length was found at 0.6 L to 0.8 L (L is the length of the building), while the optimal tree spacing distance was determined to be 3.5 m to 4.0 m in this study.

Reference:

Cui, Y., Fan, C., Zhou, X., & Liao, Y. (2025). Analysis of green belt designs in mitigating anthropogenic heat emission from buildings by considering cooling efficiency and nurture costs. Indoor + Built Environment, 34(2), 438–459. 

https://doi.org/10.1177/1420326X241300594

Relationship between urban form and heat island intensity along urban development gradients

Aims and method:

The study aimed to show the changing patterns of the relationship between urban form and urban heat island intensity along the urban development gradient based on the investigation of 150 urban areas in the Jing-Jin-Ji region in China in 2000, 2005, 2010, and 2015. A comprehensive urban development index was defined taking into account the size of the urban area, population density and night light intensity to classify the different levels of urban development. A multi-model comparison was carried out to validate the results.

Key findings:

·      As cities become more developed, factors like population density, the physical layout of buildings and streets, the shape and complexity of city edges, and the amount of urban greenery all have a stronger influence on how much heat builds up. 

·      Factors such as nighttime lighting, how stretched out a city’s shape is, and forest coverage outside the city become less important.

·      Simply limiting city size or population density doesn’t effectively reduce heat in well-developed cities. 

·      Planting trees helps reduce heat in less-developed areas, but in larger, more complex cities, a mix of other design strategies is needed to manage heat more effectively.

Reference:

Liang, Z., Wu, S., Wang, Y., Wei, F., Huang, J., Shen, J., & Li, S. (2020). The relationship between urban form and heat island intensity along the urban development gradients. The Science of the Total Environment, 708, Article 135011. 

https://doi.org/10.1016/j.scitotenv.2019.135011