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In the first of a two part article, Drs Sheeba Valsson and Alka Bharat set the framework for a fascinating study of the variations in intra-urban temperature in the city of Nagpur, India. September’s edition of AWE will see a highly detailed analysis, where elements such as seasonal temperatures and land characteristics help explain variations in microclimate.
Given the large and ever increasing number of the urban inhabitants globally, and the profound effects of cities and their inhabitants on the atmosphere, both within and beyond urban limits, it is imperative that attention is directed towards the study of urban climates.
It is particularly important to understand the variables of a climate and how urban parameters affect them, and gain a better understanding of the local climate (micro level) in urban areas. This knowledge can then easily be applied by urban planners for the betterment and comfort of the urban people.
Introduction
During the last 200 years, the global population has increased only six times, while the urban population has grown 128 times (Schell et al, 1993). India is increasingly becoming urban. According to the 2001 census, 27.8% of the Indian population resides in cities, compared with 25.5% in 1990. The urban population is expected to rise to around 40% by 2020. It is evident from the World Urbanization Prospects – the 2009 revision (United Nations 2010), that in the future there will be a significant increase in the percentage of urban population, and it is projected that by 2050, 69% of the world’s population will live in cities. It is the quality of life of these urban dwellers that needs careful planning.
The study of urban climates is important in ensuring a healthy and comfortable environment for urban dwellers and to prevent the harmful effects of urbanisation on larger scale climates (Oke, 1987).
Area of study
Nagpur is a city in the central part of India in Maharashtra State. Figure 1 shows the map of Maharashtra highlighting the position of Nagpur city. It is the third largest city in the western Indian state of Maharashtra after Mumbai and Pune.
Nagpur covers an area of about 220 km2 and lies at about 310m above mean sea level. Nagpur district is located between 21°45` N to 20°30` N and 78°15` E to 79°45` E, and is located in the Deccan Plateau (Nagpur Development Plan).
On a global scale, Nagpur is estimated to be the 114th largest city and 143rd largest urban area in the world in terms of urban population.
The climate of this region is characterised by a hot and dry summer, and well distributed rainfall during the southwest monsoon. The cold season is from December to February and is followed by the hot season from March to May. The south west monsoon season is from June to September, while the period from October until November constitutes the post monsoon season. The highest maximum temperature recorded at Nagpur was 47.8° C on May 26, 1954, and the lowest minimum was 3.9° C on January 7, 1937.
Nine urban areas
A questionnaire survey and pilot study was conducted to decide upon the urban areas in Nagpur city which were to be selected for this study. There are various factors which influence the microclimate of a particular area. This particular research was basically on the influence of the percentage of distribution of land and the street sections, and hence the basic criteria for selection of study areas was such that all the other factors influencing microclimate could be considered to be similar in the selected areas.
Based on the pilot study and the questionnaire survey nine urban areas were selected for detailed statistical analysis and to establish a relationship between the climatic parameters and the urban variables. The selected study areas are shown in Figure 2, while Table 1 gives the names of the selected areas in Nagpur city.
Regional breakdown
1. A1 – Itwari The Itwari area situated in the north east zone of Nagpur city is extremely compact. The buildings are normally three to five storeys high, with mixed land use. The streets are narrow and cut deep canyons through the area. No transport by car is possible except for a few distributor roads. The street network is irregular, which increases the mutual shading by buildings. This area has only a few trees – it is sparsely vegetated.
2. A2 – Jafer Nagar Jafer Nagar is located in the north west zone of Nagpur city. This new area of the city is a sharp contrast to the Itwari area. Buildings are outward looking and the streets, which are designed for motor vehicles, are wide and provided with wide pavements. The street pattern is regular. The buildings usually consist of single or a few double storied structures.
3. A3 – Ravi Nagar On the west zone of the city, this is a residential area with quarters for government employees. They are basically low rise structures, mainly ground and ground plus first floor structures. The street pattern is regular, wide and has wide pavements. There are wider front and rear and side marginal spaces and lots of green areas around.
4. A4 – Sadar Also on the central zone of the city, this area is extremely compact. The streets are narrow and cut deep canyons through the area. The street network is irregular which increases the mutual shading by buildings.
5. A5 – Mahal This area is situated in the south east zone of Nagpur city and is a very congested, old area with narrow and irregular streets. The buildings are normally three to five storeys high, with mixed land use. The narrow and irregular street network increases mutual shading. It is not possible to move any heavy vehicles in this area, only two wheeled or pedestrian movement is possible. Vegetation is sparse. The overhangs on roads add to the shading of the streets.
6. A6 – Wardhaman Nagar This is a residential area in the east zone of Nagpur city, where buildings are outward looking and the streets, which are designed for motor vehicles, are wide and provided with wide pavements. The street pattern is regular.
7. A7 – Friends’ Colony This is a newly developed, planned residential area in the north west zone of Nagpur city with regular wide roads and pavements. It has planned open spaces and wider, marginal open spaces around each building.
8. A8 – Medical College quarters Near Ajni railway station, this is a residential colony for the medical college doctors. It is located in the south zone of Nagpur city. They are basically single storied structures. The street pattern is regular and wide and the layout has wider front, rear and side marginal spaces and lots of green area around.
9. A9 – Government quarters – civil lines This is a residential colony for government officers in the west zone of Nagpur city. They are basically single storied structures. The street pattern is regular and wide and the layout has wider front and rear and side marginal spaces and lots of green areas around.
Air and relative humidity
Once the study areas were identified and after the detailed study of the urban parameters of the selected areas, the foundations for the work was complete. Now the on site recording of the air temperature and the relative humidity in each of the nine study areas could be done.
Summer recordings were across 12 widely scattered days from the months of April, May and June representing the summer. Thus we had data for 12 days on temperature in °C recorded at three time periods, namely 05:00hrs, 14:00 hrs and 20:00 hrs.
Similarly, the winter temperatures at these nine areas were recorded by selecting widely scattered 12 days from the months of November, December and January.
Intra-urban air temperature variation
The research work undertaken tries to find out the variation in air temperature of one area to the other in a single city. This is done in three stages. The first stage is simply to work out the intra-urban air temperature variation. The second stage is understanding the behaviour of this variation by analysing the maximum and the minimum air temperature, and their difference in each of the nine study areas. The third stage relates the variation of air temperature with the urban land characteristics of that specific area.
Summer and winter variation
From the Table 11 and Figures 14, 15 and 16 it is observed that the maximum temperature in summer ranged from 41.95° C to 49.75° C and the minimum temperature in summer ranged from 31.27° C to 35.97° C. The maximum temperature in winter ranged from 24.03° C to 29.40° C and the minimum temperature in winter ranged from 18.12° C to 21.90° C.
There are a significant intra-urban air temperature variations – both maximum and minimum temperature – in the selected study areas.
References
1. Oke TR (1981), Canyon Geometry and the nocturnal urban heat island; Comparision of scale model and field observation, Journal of Climatology,Vol 1,237-254. 2. Oke, TR(1982) The energetic Basis of URBAN Heat Island, Quarterly Journal of the Royal meteorological Society, Vol.108(455), 1-24. 3. Oke, TR (1987). Boundary layer climates. London: William Clowes and Sons, pp 33-76. 4. Oke, TR (1988) Street design and urban canopy layer climate. Energy and Buildings, Vol. 11, 103-113. 5. Oke TR, Johnson GT, Steyn DG and Watson ID,(1991) Simulation of surface urban heat islands under ideal conditions at Night-part 2- Diagnosis and Causation, Bombay Layer Meteorology, Vol.56, 339-358. 6. Schell LM, Smith MT and Billsborough A,(1993) Human biological approaches to the study of third world urbanism, Urban ecology and health in the 3rd world, Cambridge University Press, pp 1-9. 7. United Nations, Department of Economic and Social Affairs, Population Division, World Urbanization Prospects: The 2009 revision, CD-Rom Edition – Data in digital form (POP/DB/WUP/Rev. 2009) http://esa.un.org/unpd/wup/index.htm, 2010). 8. Valsson Sheeba (2012) unpublished PhD Project titled Assessment of Microclimate variation in context to Urban Development.
Published: 31st May 2013 in AWE International
