Cooling the Urban Environments and its Impact on Climate Change in Informal Settlements through Outdoor Thermal Comfort (Case Studies: Aa’melli, Ghaleh Sakhteman and Hojjat Neighborhoods of Mashhad)

Document Type : Research Paper


1 Department of Architecture, Faculty of Architectural and Urban Engineering, Shahrood University of Technology, Shahrood, Iran

2 Young and Elite Researchers Club, Mashhad Branch, Islamic Azad University, Mashhad, Iran


The climate becomes warmer than ever before, as evidenced by numerous observations and modeling that has in turn created a warming climate in cities. Therefore, various climate change projects and attention to heatwaves in recent centuries have been considered and the increase in population and its activities in various fields have caused problems such as heatwaves around the world. In addition, changing the pattern of occurrence of these changes and their unpredictability has led to an increase in the number of them in cities and to reduce concerns and adapt to these risks in various aspects of urban life, especially human health, to create sustainable urban forms. This phenomenon has caused the death of thousands of people in the world, and one of the important reasons for this is the flaw of the cities to deal with the increase in heatwaves. While different changes and global warming can affect urban areas, urban areas can also exacerbate these changes. Rising urbanization rates and people's desire to live in cities have led to higher urban temperatures than their surroundings. Studies show that a city with a population of one million people has experienced an increase in temperature between 1 and 12 degrees. This increase in temperature is due to the structure of cities, which has many negative effects and consequences for cities, so urban environments should be planned and designed in such a way as to improve the health of individuals and thus the presence in public spaces of cities. Urban forms such as urban canyons and vegetation at the pedestrian level are among the factors affecting the reduction of urban temperatures in urban areas and neighborhoods, the impact of these factors on the outdoor thermal comfort of humans by few research in Iran has been considered. A review of the research background of the subject shows that no serious attention has been paid to the native urban forms of Iran as a factor for reducing urban heat and promoting human health; However, local urban planning helps architects and planners to address urban problems by identifying needs in indoor and outdoor environments to provide the most effective way to reduce the severity of outdoor environments using all design elements. Given that there is still, no place to pay attention to how urban forms change in order to reduce the effects of climate change and outdoor thermal comfort professionally, so the present study focuses on the impact of urban forms on informal settlements and old textures on outdoor thermal comfort. The ambient air temperature and the creation of outdoor thermal comfort in the city of Mashhad, which is one of the cities that experience the most urban forms of informal settlements. The present article, firstly, examines the research done in the thematic field of the article and then in the next part, the theoretical framework is extracted by using articles, dissertations, and books. In the third part of this framework, using simulation in Envi-met software and PET index output in Rayman software and analysis in Leonardo to identify the effects of urban forms on air the temperature in microclimate and outdoor thermal comfort using physiological equivalent temperature index (PET). Studies conducted in the summer and on August 26, 2019, have been selected due to the high heat of the sun and its effect on creating outdoor thermal comfort in open urban spaces.
Materials and Methods,
Due to the nature of the subject, the research method is applied and based on two parts. In the first part, the documentary method is used to formulate the theoretical framework. Thus, by referring to articles, treatises, and books by taking notes, the information needed to understand the thematic literature as well as studies conducted in the field of research has been collected and then using descriptive and analytical methods to prepare and compile the conceptual framework of research. In the next part of the research, the case study was studied and the maps were extracted using GIS. The method of survey and harvesting of climatic information from the Mashhad Climate Organization has been used to collect climatic data. In order to identify the effects of the influential components of the urban form, the Envi-met 4 and Leonardo software collections as well as Rayman have been used. In this study, most simulations were performed in summer (August) and based on data from Mashhad Meteorological Station. This simulation was selected on August 17, 2019, and at sunrise and sunset between 6:00 AM and 8:00 PM local time due to the high temperature of the sun and its effect on ambient temperature and surfaces in open urban spaces. This simulation lasted for 156 hours for three urban forms.
Discussion of Results
The present study investigates the outdoor thermal comfort in informal settlements in Mashhad. Various studies have shown that lowering the ambient temperature in summer can reduce environmental thermal stress and thus improve outdoor thermal comfort. The results in this paper suggest that as the height-to-width (H / W) ratio increases, the sun's access to the environment decreases, and the amount of shading on the surfaces increases resulting in a decrease in ambient temperature. Therefore, it can be said that the height-to-width (H / W) ratio is inversely related to the ambient temperature, and urban form factors such as the height-to-width ratio (H / W) and its shading play an important role in reducing the ambient temperature. On the other hand, the simulations performed to show the temperature difference, so that the difference between the mean indexes (PET) during the hours of thermal stress are 0.68 ° C, 2.53 ° C and 3.27 ° C. The heat stress of the Hojjat fabric is greater than that of the other two fabric and there are more hours in the absence of outdoor thermal comfort, which indicates the temperature difference in all three fabric; but the same the difference stems from different environmental parameters in the three urban forms. One of these parameters is the coverage of outdoor surfaces and materials used in the outer shell of buildings, which is indicated by the Tmrt average temperature index as an important parameter in creating thermal equilibrium in the environment. Studies show that the average temperature index of radiant temperature (Tmrt) is directly related to the PET index and the higher the average temperature index of radiant temperature, the higher the PET index, and vice versa, therefore, the high average radiant temperature in the texture of Hojjat compared to the texture of the agent and the Ghale of the building in the peak hours of heat shows the high rate of heat reflection to the environment in the texture of Hojjat compared to the other two textures. Higher average radiant temperature (Tmrt) in the texture of Hojjat means reflecting more heat than urban levels and can be closely related to the materials used in this texture and the amount of sun access and thus the effect of height to width ratio (H / W) on the ambient temperature. And have levels. Due to the color and texture of the brick, it absorbs less heat and gradually releases the hidden heat and its heat exchange with the environment during the night hours when the air cools down. On the other hand, the temperature a difference of 0.68 C in the first and last hours of simulation in the operating tissue shows that the use of brick materials can reduce the heat exchange with the environment and thus reduce the ambient temperature.


امیر فخریان، م. رهنما،.م.م، آقاجانی، ح،(1391). اولویت‌بندی نیاز به خدمات بهداشتی درمانی محلات حاشیه‌نشین شهر مشهد بر اساس سیستم پشتیبانی فضایی چند معیاره. مجله آمایش جغرافیایی فضا، 2(6)،صص 36-17.
ثناگر دربانی،ا. رفیعیان.م. حنایی،ت. منصفی پراپری.د،(1396). اثرات زیست‌محیطی تغییرات هندسه بافت شهری بر دمای محیط و آسایش حرارتی بیرونی در اقلیم خشک شهر مشهد (نمونه موردی بافت قدیمی پاچنار و بافت جدید شاهد). محیط شناسی،43 (4)، صص 578-561.
حیدری، ش. و منعام، ع،(1392). ارزیابی شاخصه‌های آسایش حرارتی در فضای باز. جغرافیا و توسعه ناحیه‌ای،11(20)، صص 216-197.
ذوالفقاری، ح،(1386). تعیین تقویم زمانی مناسب برای گردش در تبریز با استفاده ازشاخص و متوسط نظرسنجی پیش بینی شده PMV و دمای معادل فیزیولوژی(PET). پژوهش‌های جغرافیایی،39 (62)، صص 141-129.
مهندسین مشاور فرنهاد، (1388). گزارش مطالعات پایه محیط انسان‌ساخت جلد مسکن و نحوه سکونت، جلد اول.
Abreu-Harbich ,L. V., Labaki, L. C., & Matzarakis, A.(2014). Thermal bioclimate in idealized urban street canyons in Campinas, Brazil. Theoretical and Applied Climatology, 115(2-1),115-223.
Akbari, H.(2005).Energy Saving Potentials and Air Quality Benefits of Urban HeatIslandMitigation, Lawrence Berkeley National Laboratory: Lawrence Berkeley National Laboratory.
Akbari, H., Bretz, S., Kurn, D. M. and Hanford, J.(1997). Peak power and cooling energy savings of high-albedo roofs. Energy and Buildings, 25(2),117-126.
Amirtham, L. R.(2010).Effect of urbanization on urban heat island and thermal comfort in chennai metropolitan area(PHD Thesis), Anna University.
Baruti, M. M., Johansson, E., & Åstrand, J.(2019). Review of studies on outdoor thermal comfort in warm humid climates: challenges of informal urban fabric. International Journal of Biometeorology, 63(10),1449-1462.
Bramley, G., & Kirk, K.(2005). Does Planning Make a Difference to Urban Form? Recent Evidence from Central Scotland. Environment and Planning, 37(2),355-378
Bruse, M.(1999). The Influences of Local Environmental Design on Microclimate Development of a Prognostic Numerical Model ENVI-Met for the Simulation of Wind, Temperature and Humidity Distribution in Urban Structures(PHD Thesis). University of Bochum.
Clifton, K., Ewing, R., Knaap, G. J., & Song, Y.(2008). Quantitative analysis of urban form: a multidisciplinary review. Journal of Urbanism: International Research on Placemaking and Urban Sustainability,1(1),17-45.
Cuthbert, A. L., & Anderson, W. P.(2002).An examination of urban form in Halifax-Dartmouth: Alternative approaches in data. Canadian Journal of Urban Research,11(2),213-237. 
Dai, Q.(2014).The Impact of Urban Form on Thermal Comfort across Street Zones(PHD Thesis), The Chinese University of Hong Kong.
Dempsey, N., Brown, C., Raman, S., Porta, S., Jenks, M., Jones, C., & Bramley, G.(2010) .Elements of Urban Form. Dordrecht, Springer Netherlands.
Erell, E., Pearlmutter, D. , &Williamson, T. J.(2011) .Urban Microclimate: Designing the Spaces Between Buildings. Taylor & Francis.
Fabbri, K.(2015).Indoor Thermal Comfort Perception :A Questionnaire Approach Focusing on Children. Switzerland, Springer International Publishing.
Fanger, P.(1970).Thermal comfort. Analysis and applications in environmental engineering. Danish Technical Press, Copenhagen, Denmark
Fröhlich, D. , &Matzarakis, A.(2013). Modeling of Changes in Human Thermal Bioclimate Resulting from Changes in Urban Design: Example Based on a Popular Place in Freiburg, Southwest Germany. Theoretical and Applied Climatolog,443-449.
Galal, O. M., Mahmoud, H., & Sailor, D.(2020).Impact of evolving building morphology on microclimate in a hot arid climate. Sustainable Cities and Society,54,102011 .
Gambo Hamza ,Y., Ameta, S., Tukur, A. , & Usman, A.(2020). Overview on Evidence and Reality of Climate Change. Journal of Environmental Science Toxicology and Food Technology, 14,17-26. 
Höppe, P.(1999). The physiological equivalent temperature–a universal index for the assessment of the thermal environment. International Journal of Biometeorol, 43,71-75.
Horrison, E. , &Amirtham, L.(2016). Role of Built Environment on Factors Affecting Outdoor Thermal Comfort - A Case of T. Nagar, Chennai, India. Indian Journal of Science and Technology, 9(5),1-4.
IPCC.(2007).Climate Change Synthesis Report – Summary for Policymakers. Cambridge University Press, Assessment of Working roups I, II, and III. the Third Assessment Report of the International Panel on Climate Change.
IPCC.(2018).Global Warming of 1.5°C. Intergovernmental Panel on Climate Change Special Report. Geneva, Switzerland.
Irger, M.(2014).The Effect Of Urban Form On Urban Microclimate(PHD Thesis). The University of New South Wales
Jamei, E. , & Rajagopalan, P.(2018). Effect of street design on pedestrian thermal comfort. Architectural Science Review, 11(2),62-92.
Lee, H. , &Mayer, H.(2018). Thermal comfort of pedestrians in an urban street canyon is affected by increasing albedo of building walls. International Journal of Biometeorology, 62.
Lee, L. S. H. , & Jim, C. Y.(2019).Urban woodland on intensive green roof improved outdoor thermal comfort in subtropical summer. International Journal of Biometeorology, 63(7),895-909.
Matzarakis, A., & Mayer, H.(1996). Another kind of environmental stress: thermal stress. WHO Colloborating Centre for Air Quality Management and Air Pollution Control Newsletter,18,7-10.   
Matzarakis, A., Mayer, H., &Iziomon, M.(1999). Applications of a universal thermal index: physiological equivalent temperature. International Journal of Biometeorology,43(2),76-84. 
Matzarakis, A., Rutz, F, & Mayer, H.(2007). Modelling radiation fluxes in simple and complex environments: basics of the RayMan model. International Journal of Biometeorology, 54(2), 131-139
Mayer, H., &Höppe, P.(1987). Thermal comfort of man in different urban environments. Theor Appl Climatol,38, 43-49.
Muniz-Gäal, L. P., Pezzuto, C. C., Carvalho, M. F. H. d., &Mota, L. T. M.(2020). Urban geometry and the microclimate of street canyons in tropical climate. Building and Environment,169, 106547
Oke, T.R. (1987). Boundary Layer Climates. 2nd Edition, Methuen Co., London, New York,
Oke, T. R. (2006).Initial guidance to obtain representative meteorological observations at urban sites. WHO/TD.
Oliver, J. E.(2005).Encyclopedia Of World Climatology .Springer Netherlands.
Oliveira, V.(2016). Urban Morphology an Introduction to the Study of the Physical Form of Cities. Springer International Publishing
Peng ,Y., Feng, T., &Timmermans, H.(2019). A path analysis of outdoor comfort in urban public spaces.Building and Environment, 148,459-467.
Prasad, N., Ranghieri, F., Shah, F., &Trohanis, Z.(2009). Climate Resilient Cities : A Primer on Reducing Vulnerabilities to Disasters. Washington, DC, World Bank.
Roaf, S., Crichton, D., &Nicol, F.(2009).Adapting Buildings and Cities for Climate Change: A 21st Century Survival Guide. Oxford, United Kingdom, Taylor & Francis Ltd.
Santamouris, M., Adnot, J., Klitsikas, N., Orphelin, M., Lopes, C, & Sanchez, F.(2004).Cooling the cities: Energy Efficent Cooling systems and techniques for urban buildings. Greece, university of Paris.
Saud Alznafer, B. M.(2014).The impact of neighbourhood geometries on outdoor thermal comfort and energy consumption from urban dwellings a case study of the riyadh city, the kingdom of saudi arabia(PHD Thesis), Cardiff University.
Sen, S. and Roesler, J.(2020). Wind direction and cool surface strategies on microscale urban heat island.Urban Climate,  31,100548.
Shahmohamadi, P., Che-Ani, A. I., Etessam, I., Maulud, K. N. A., &Tawil, N. M.(2011). Healthy Environment: The Need to Mitigate Urban Heat Island Effects on Human Health. Procedia Engineering,  20(Supplement C),61-70.
Szokolay S. V.2008.Architectural Science The Basis Of Sustainable Design, Elsevier.
Xiong, Y., Zhang, J., Xu, X., Yan, Y., Sun, S., &Liu, S.(2020). Strategies for improving the microclimate and thermal comfort of a classical Chinese garden in the hot-summer and cold-winter zone. Energy and Buildings, 215.109914.
Yang W., Wong, N. H., & Lin, Y.(2015). Thermal Comfort in High-rise Urban Environments in Singapore. Procedia Engineering,  121(Supplement C) ,2125-2131
Yıldırım ,M.(2020). Shading in the outdoor environments of climate-friendly hot and dry historical streets: The passageways of Sanliurfa, Turkey. Environmental Impact Assessment Review80,1-11.
Yang, W., Wong, N. H., & Li, C.-Q.( 2016). Effect of Street Design on Outdoor Thermal Comfort in an Urban Street in Singapore. Journal of Urban Planning and Development,142(1),1-19.