Three new online articles of the group

Gepubliceerd op
19 maart 2015

Wiebke Klemm and Sanda Lenzholzer


Thermal comfort of outdoor spaces in Lahore Pakistan: Lessons for bioclimatic urban design in the context of global climate change

by: Mazhar, Naveed, Brown, Robert D., Kenny, Natasha, Lenzholzer, Sanda

in: Landscape and Urban Planning, February 2015

online link:

Abstract: Humans interact with urban microclimates through exchanges of energy. A surplus of energy can create thermal discomfort and be detrimental to human health. Many cities in warm regions all over the world are forecast to become very hot through global climate change. Some cities already experience extreme heat and have done so for centuries. We conducted a study of one such city in order to generate design guidelines for creating thermally comfortable outdoor places. In the hot, dry city of Lahore, Pakistan we compared the microclimates of two very different outdoor spaces. The first place was the 16th century Shalimar Garden, which contains much green infrastructure and water features. The other example was the hard-surfaced courtyard of the contemporary Alhamra Art Centre. In both places we measured the microclimatic characteristics and used those data to simulate thermal sensation through the energy-budget model COMFA. The measured air temperature and humidity in both spaces was similar. However, the solar radiation that would be received by a person in the Alhamra courtyard was much higher than in Shalimar Garden and was the main determinant of thermal discomfort. Results from this study can inform other cities in hot, dry climates about design responses that provide more outdoor thermal comfort and prevent health-threatening heat.


Street greenery and its physical and psychological impact on outdoor thermal comfort

by: Klemm, W. (1e), Heusinkveld, B., Lenzholzer, S., Van Hove, B.

in: Landscape and Urban Planning, February 2015

online link: 

Abstract: This study focuses on the benefits of street greenery for creating thermally comfortable streetscapes in moderate climates. It reports on investigations on the impact of street greenery on outdoor thermal comfort from a physical and psychological perspective. For this purpose, we examined nine streets with comparable geometric configurations, but varying amount of street greenery (street trees, front gardens) in the city of Utrecht, the Netherlands. Mobile micrometeorological measurements including air temperature (Ta), solar and thermal radiation were performed, enabling the calculation of mean radiant temperature (Tmrt). Additionally, semi-structured interviews with pedestrians about their momentary and long-term perceived thermal comfort and their esthetical appreciation of the green street design were conducted. Measurements showed a clear impact (p = 0.0001) of street greenery on thermal comfort through tree shading: 10% tree crown cover within a street canyon lowered street averaged Tmrt about 1 K. In contrast, our results did not show an influence of street greenery on street averaged Ta. Interview results indicated that momentary perceived thermal comfort tended to be related to the amount of street greenery. However, the results were not statistically significant. Related to long-term perceived thermal comfort respondents were hardly consciously aware of influences by street greenery. Yet, people significantly (p < 0.001) valued the presence of street greenery in esthetic terms. In conclusion, street greenery forms a convenient adaptive strategy to create thermally comfortable and attractive living environments. Our results clearly indicate that both physical and psychological aspects of thermal comfort have to be considered in urban design processes.


Designing urban parks that ameliorate the effects of climate change

by: Brown, Robert D., Vanos, Jennifer, Kenny, Natasha, Lenzholzer, Sanda

in: Landscape and Urban Planning, February 2015

online link:

Abstract: Many inhabitants of cities throughout the world suffer from health problems and discomfort that are caused by overheating of urban areas, and there is compelling evidence that these problems will be exacerbated by global climate change. Most cities are not designed to ameliorate these effects although it is well-known that this is possible, especially through evidence-based climate-responsive design of urban open spaces. Urban parks and green spaces have the potential to provide thermally comfortable environments and help reduce vulnerability to heat stress. However, in order for them to provide this function, parks must be designed within the context of the prevailing climate and predicted future climates. To analyze the effects of elements that alter microclimate in parks, we used human energy budget simulations. We modelled the outdoor human energy budget in a range of warm to hot climate zones and interpreted the results in terms of thermal comfort and health vulnerability. Reduction of solar radiant input with trees had the greatest effect in all test cities. Reduction in air temperature was the second-most important component, and in some climates was nearly as important as incorporating shade. We then conducted similar modelling using predicted climates for the middle of the century, emphasizing the importance of city-level efforts for park design to assist in minimizing future climate-related urban health risks. These simulations suggested that heat waves in many climates will produce outdoor environments where people will be in extreme danger of heat stress, but that appropriately designed parks can reduce the threat.