A long-term simulation of urban climate was done using the easily available long-term meteorological data from a nearby synoptic station in a tropical coastal city of Dar es Salaam, Tanzania. The study aimed at determining the effects of buildings’ height and street orientations on human thermal conditions at pedestrian level. The urban configuration was represented by a typical urban street and a small urban park near the seaside. The simulations were conducted in the microscale applied climate model of RayMan, and results were interpreted in terms of the thermal comfort parameters of mean radiant ( ) and physiologically equivalent (PET) temperatures. PET values, high as 34°C, are observed to prevail during the afternoons especially in the east-west oriented streets, and buildings’ height of 5？m has less effect on the thermal comfort. The optimal reduction of and PET values for pedestrians was observed on the nearly north-south reoriented streets and with increased buildings’ height especially close to 100？m. Likewise, buildings close to the park enhance comfort conditions in the park through additional shadow. The study provides design implications and management of open spaces like urban parks in cities for the sake of improving thermal comfort conditions for pedestrians. 1. Introduction Dar es Salaam is a hot, humid tropical city situated along the Tanzanian coast on the Western Indian Ocean coast. It enjoys the sea-land breezes system which is observed to be more organised during the months of March, April, September, and October [1, 2]. On the other hand, sultriness is not uncommon particularly during the December–February (DJF) season. Such sultry conditions bring an undesirable thermal discomfort especially to pedestrians and street vendors. Most biometeorological studies done elsewhere have revealed the effects of street orientation and height to width ratio on the variation of local thermal comfort at an urban canyon level [3–6]. Although the human thermal comfort is influenced by four meteorological parameters of air temperature, humidity, wind speed, and radiation flux (usually quantified in terms of mean radiant temperature), it is the wind speed and mean radiant temperature which can be significantly varied by changing the street orientation and height to width ratio [7]. A past urban climate research in Dar es Salaam has suggested that the observed sea-land breeze effect could improve the thermal comfort at high ground places in the city like at the university of Dar es Salaam campus which is about 12？km to the west from the city centre
References
[1]
S. Nieuwolt, “Breezes along the Tanzanian East Coast,” Archiv für Meteorologie Geophysik und Bioklimatologie B, vol. 21, no. 2-3, pp. 189–206, 1973.
[2]
E. L. Ndetto and A. Matzarakis, “Basic analysis of climate and urban bioclimate of Dar es Salaam, Tanzania,” Theoretical and Applied Climatology, 2013.
[3]
F. Ali-Toudert and H. Mayer, “Thermal comfort in an east-west oriented street canyon in Freiburg (Germany) under hot summer conditions,” Theoretical and Applied Climatology, vol. 87, no. 1–4, pp. 223–237, 2007.
[4]
I. Charalampopoulos, I. Tsiros, A. Chronopoulou-Sereli, and A. Matzarakis, “Analysis of thermal bioclimate in various urban configurations in Athens, Greece,” Urban Ecosystems, vol. 16, no. 2, pp. 217–233, 2013.
[5]
F. Bourbia and F. Boucheriba, “Impact of street design on urban microclimate for semi arid climate (Constantine),” Renewable Energy, vol. 35, no. 2, pp. 343–347, 2010.
[6]
F. Ali-Toudert and H. Mayer, “Numerical study on the effects of aspect ratio and orientation of an urban street canyon on outdoor thermal comfort in hot and dry climate,” Building and Environment, vol. 41, no. 2, pp. 94–108, 2006.
[7]
T.-P. Lin, A. Matzarakis, and R.-L. Hwang, “Shading effect on long-term outdoor thermal comfort,” Building and Environment, vol. 45, no. 1, pp. 213–221, 2010.
[8]
E. Johansson, “Influence of urban geometry on outdoor thermal comfort in a hot dry climate: a study in Fez, Morocco,” Building and Environment, vol. 41, no. 10, pp. 1326–1338, 2006.
[9]
H. Sugawara, A. Hagishima, K. Narita, H. Ogawa, and M. Yamano, “Temperature and wind distribution in an EW-oriented urban street canyon,” Scientific Online Letters of the Atmosphere (SOLA), vol. 4, pp. 53–56, 2008.
[10]
R. Emmanuel and E. Johansson, “Influence of urban morphology and sea breeze on hot humid microclimate: the case of Colombo, Sri Lanka,” Climate Research, vol. 30, no. 3, pp. 189–200, 2006.
[11]
E. Johansson and R. Emmanuel, “The influence of urban design on outdoor thermal comfort in the hot, humid city of Colombo, Sri Lanka,” International Journal of Biometeorology, vol. 51, no. 2, pp. 119–133, 2006.
[12]
A. Lopes, S. Lopes, A. Matzarakis, and M. J. Alcoforado, “The influence of the summer sea breeze on thermal comfort in funchal (Madeira). A contribution to tourism and urban planning,” Meteorologische Zeitschrift, vol. 20, no. 5, pp. 553–564, 2011.
[13]
S. Ahmad, N. M. Hashim, Y. M. Jani, and N. Ali, “The impacts of sea breeze on urban thermal environment in tropical coastal area,” Advances in Natural and Applied Sciences, vol. 6, no. 1, pp. 71–78, 2012.
[14]
E. L. Krüger and F. A. Rossi, “Effect of personal and microclimatic variables on observed thermal sensation from a field study in southern Brazil,” Building and Environment, vol. 46, no. 3, pp. 690–697, 2011.
[15]
R. Emmanuel, H. Rosenlund, and E. Johansson, “Urban shading—a design option for the tropics? A study in Colombo, Sri Lanka,” International Journal of Climatology, vol. 27, no. 14, pp. 1995–2004, 2007.
[16]
A. Matzarakis, F. Rutz, and H. Mayer, “Modelling radiation fluxes in simple and complex environments—application of the RayMan model,” International Journal of Biometeorology, vol. 51, no. 4, pp. 323–334, 2007.
[17]
A. Matzarakis, F. Rutz, and H. Mayer, “Modelling radiation fluxes in simple and complex environments: basics of the RayMan model,” International Journal of Biometeorology, vol. 54, no. 2, pp. 131–139, 2010.
[18]
S. Thorsson, F. Lindberg, I. Eliasson, and B. Holmer, “Different methods for estimating the mean radiant temperature in an outdoor urban setting,” International Journal of Climatology, vol. 27, no. 14, pp. 1983–1993, 2007.
[19]
P. Jonsson, C. Bennet, I. Eliasson, and E. Selin Lindgren, “Suspended particulate matter and its relations to the urban climate in Dar es Salaam, Tanzania,” Atmospheric Environment, vol. 38, no. 25, pp. 4175–4181, 2004.
[20]
S. E. Mbuligwe and G. R. Kassenga, “Automobile air pollution in Dar es Salaam City, Tanzania,” Science of the Total Environment, vol. 199, no. 3, pp. 227–235, 1997.
[21]
A. Hill and C. Lindner, Modelling Informal Urban Growth Under Rapid Urbanisation: A CA-Based Land-Use Simulation Model for the City of Dar Es Salaam, Tanzania, Technische Universit？t Dortmund, Dortmund, Germany, 2010.
[22]
F. R. Fosberg, B. J. Garnier, and A. W. Küchler, “Delimitation of the humid tropics,” Geographical Review, vol. 51, no. 3, pp. 333–347, 1961.
[23]
M. Roth, “Review of urban climate research in (sub)tropical regions,” International Journal of Climatology, vol. 27, no. 14, pp. 1859–1873, 2007.
[24]
C. Howorth, I. Convery, and P. O'Keefe, “Gardening to reduce hazard: urban agriculture in Tanzania,” Land Degradation and Development, vol. 12, no. 3, pp. 285–291, 2001.
[25]
W. Kuttler, “Stadtklimain,” in Handbuch der Umweltver？nderungen und ？kotoxologie, R. Guderian, Ed., pp. 420–470, Springer, Berlin, Germany.
[26]
A. Matzarakis, M. Rocco, and G. Najjar, “Thermal bioclimate in Strasbourg-the 2003 heat wave,” Theoretical and Applied Climatology, vol. 98, no. 3-4, pp. 209–220, 2009.
[27]
M. G. Kendall, “A new measure of rank correlation,” Biometrika, vol. 30, no. 1/2, pp. 81–93, 1938.
[28]
A. Matzarakis, H. Mayer, and M. G. Iziomon, “Applications of a universal thermal index: physiological equivalent temperature,” International Journal of Biometeorology, vol. 43, no. 2, pp. 76–84, 1999.
[29]
H. Mayer and P. H？ppe, “Thermal comfort of man in different urban environments,” Theoretical and Applied Climatology, vol. 38, no. 1, pp. 43–49, 1987.
[30]
P. H？ppe, “The physiological equivalent temperature—a universal index for the biometeorological assessment of the thermal environment,” International Journal of Biometeorology, vol. 43, no. 2, pp. 71–75, 1999.
[31]
D. J. Wessel, Ashrae Fundamentals Handbook 2001, ASHRAE, Atlanta, Ga, USA, 2001.
[32]
A. Matzarakis, F. Rutz, and H. Mayer, “Modelling radiation fluxes in simple and complex environments—application of the RayMan model,” International Journal of Biometeorology, vol. 51, no. 4, pp. 323–334, 2007.
[33]
G. L. Makokha and C. A. Shisanya, “Trends in mean annual minimum and maximum near surface temperature in Nairobi City, Kenya,” Advances in Meteorology, vol. 2010, Article ID 676041, 6 pages, 2010.
[34]
O. Akinbode, A. Eludoyin, and O. Fashae, “Temperature and relative humidity distributions in a medium-size administrative town in southwest Nigeria,” Journal of Environmental Management, vol. 87, no. 1, pp. 95–105, 2008.
[35]
R. Emmanuel, “Thermal comfort implications of urbanization in a warm-humid city: the Colombo Metropolitan Region (CMR), Sri Lanka,” Building and Environment, vol. 40, no. 12, pp. 1591–1601, 2005.
[36]
C. Grimmond, S. Potter, H. Zutter, and C. Souch, “Rapid methods to estimate sky-view factors applied to urban areas,” International Journal of Climatology, vol. 21, no. 7, pp. 903–913, 2001.
[37]
N. D. Burgess and G. P. Clarke, Coastal Forests of Eastern Africa, IUCN, Gland, Switzerland, 2000.
[38]
J. Herrmann and A. Matzarakis, “Mean radiant temperature in idealised urban canyons-examples from Freiburg, Germany,” International Journal of Biometeorology, vol. 56, no. 1, pp. 199–203, 2012.
