Impact of Urbanization and Land Use
Changes on Climate
Govindu Vanum
Asst.Professor, Geo-Information and Earth Observation Sciences, Mekelle University, Mekelle, Ethiopia.
International Journal of Physical and Social Sciences IJPSS, Volume 2, Issue 9, September 2012, PP 414 - 432:
ABSTRACT
The study examines the effects of urbanization and land use changes on climatic environment of Visakhapatnam city. A detailed study was carried out with regard to urban heat islands and to examine the nature and intensity of heat islands in the city. This study is very important in city planning for the avoidance of air pollution hazards. Trend analysis of the temperatures has been carried out in order to assess the effects of urbanization on thermal climate. The regression analysis gives an indication of overall tendency of the temperature. The mean annual temperature varies from 23.5°c to 30.9°c; mean maximum summer (April-June) temperature varies from 32.8°c – 34.0°c and mean minimum winter (Dec – Feb) temperature ranges from 17.5°c – 19.3°c. The mean annual rainfall is 954mm and Visakhapatnam receives maximum amount of rainfall during post monsoon period (Oct-Nov) due to cyclonic activity. The trends of both annual and monsoonal rainfall at Visakhapatnam over a period of 50 years, from 1951 to 2000 are also examined.
INTRODUCTION
With the increasing emphasis on planning for healthier and comfortable physical environment in cities, the need to recognize the role of cities in creating climatic change has become greater. This paper on climate impacts of urbanization demonstrates that the rapid urbanization and land use changes and their influence in modifying or creating climates which add to the city residents discomfort and even ill health. It is recognized that the climate of cities generally tend to be warmer than those of the surrounding countryside. Cities differ from the countryside not only in respect of their temperature but also in respect of other climatic elements. Very often, the city itself is the cause of climatic differences. Its compact mass of buildings and pavements and urban activities of its inhabitant are a considerable source of heat. Each city has its own landscape profile and thereby has its own climate. Hence it is difficult to infer the climate of all cities by generalizing from observations within one or a few cities.
Urbanization is one phenomenon that may cause changes in local and even regional climate. Urban development has introduced changes in land surface characteristics which in turn have changed the local climate into what can be defined as “urban climate”. The natural environment found in the rural side favored by an equable climate blessed with clean air and ample pure water, is indeed a wondrous and a most precious resource for mankind. Urban climates are mostly inferior in quality to rural climates, especially in relation to human health and well-being. It is clear that cities are warmer, cloudier, less sunny and less humid than surrounding rural environments. The city atmosphere is liable to pollution, greenhouse gases, dust, smoke and smog. These have the effects of changing the thermal properties of the atmosphere, cutting down the passage of sunlight and providing abundant condensation nuclei. The increase of particulate matter in the atmosphere is bound to affect the climate since particles not only scatter and absorb solar radiation but also have an effect on the outgoing radiation from the surface of the earth. Consequently cities receive less solar radiation than rural areas. And there is yet another fact, that cities have 10 per cent or more clouds which also affect the incoming solar radiation. City wind speeds are lower than those in the surrounding open country, owing to the scattering effect of the buildings and blocks (Landsberg, 1970). Another important distinguishing element between the urban and rural settings having a strong climatic impact is the vegetation cover. Rural areas have lower humilities as they are surrounded by agricultural lands and natural vegetation.
STUDY AREA
The present study discusses the effects of urbanization on climatic environment of Visakhapatnam city, Andhra Pradesh, India. The study with regard to urban micro climate is confined to Visakhapatnam main city area only. Based on topographical conditions, the city and its environs can be divided into four categories viz., hill ranges, upland area, central plain region and coastal zone. Visakhapatnam enjoys a characteristic tropical maritime climate. All the elements of the climate – temperature, rainfall, wind and humidity hardly exhibit well marked seasonal variations. Its natural local climate owes its origin to the peculiar topography on the north and on the south and the vast water body on the east contributing to the interesting land and sea breeze circulations.
METHODOLOGY
The most obvious method for the measurement of the temperatures over a city is to take observations at a number of locations simultaneously which require considerable equipment and man power. To facilitate the adequate coverage of the entire city some 12 traverses have been selected, each traverse covering about 15 to 20 pre-selected representative spots, in each section of the city. The observation period was near the minimum temperature epoch, when the heat island effects are known to be most prominent. Days with clear skies and calm winds were chosen as far as possible. On the day of observation, the survey was started form a suitable terminal point of the traverse. Surface temperature data were collected using thermometers at a number of predetermined points. Observations were completed as quickly as possible in order to minimize the effect of time changes during the observation period. The surveys were always terminated with repetition of observation at the starting point and observations were reduced to a common time base. Thermographs were also installed at representative locations to know the temperature trends. The observational points were so chosen as to ensure adequate representation of all parts (residential, commercial, industrial etc.) of the city. The temperatures were then plotted on a map of the city and isotherms were drawn taking topography into consideration. The survey programmes were conducted periodically and the temperature data for Visakhapatnam were obtained on representative days during the winter season and also summer season during the years 2007- 2008 and 2009.
CONCLUSION
The rapid urbanization, industrialization and land use / land cover changes have brought about micro climatic changes particularly with regard to its thermal structure. The well documented climatic modification of the city is urban heat island. The study reveals that heat islands can be found under all meteorological conditions during all seasons and but heat islands of higher intensities are observed only during winter season under calm conditions. At Visakhapatnam the formation of heat island is controlled by topography and urban morphology. The land and sea breeze circulation also interacts with the heat island. Hence, intensity of heat island is 3°c to 4°C at Visakhapatnam unlike other Indian cities where the intensities are more than 4°c. This study is important in city planning for the avoidance of possible air pollution hazards. Heat island also causes human discomfort during heat wave conditions of summer.
The rate of cooling of urban and rural environments also differs widely due to marked different land surfaces. Field surveys were conducted to observe cooling rates between urban and rural environment. Analysis of hourly temperature data reveals that the rate of decrease of temperature or cooling rate is 0.4°c / hr at urban centre of Visakhapatnam, 0.8°c / hr at sub-urban and 1.0°c / hr at rural area. Trend analysis of the temperatures has been carried out to assess the affect of urbanization on thermal climate. Trends of maximum and minimum temperatures have been evaluated by linear regression analysis. It is observed that there is an increasing trend of maximum temperature of 0.2°c / 40 years but trend is insignificant. With regard to minimum temperature, there is significant increasing trend of temperature i.e. 0.7°c over a period of 40 years. Trend analysis of both annual and seasonal rainfall (monsoon) has been carried out to observe temporal variations in rainfall. The results reveal that there is an increasing trend of rainfall both in annual and seasonal distributions over a period of 50 years i.e. 1951 – 2000
Proper application of climatic knowledge in land use, urbanization and building design can contribute to improved human health, environment, energy usage and other social and economic benefits.
REFERENCES
1. Greater London Authority, 2006b. London‟s Urban Heat Island: A Summary for Decision Makers. Greater London Authority, London.
2. Krishna, T.V., and Sachidevi.S., 2007. A study on surface Temperature Trends over Andhra Pradesh. The Indian Geographical Journal 81(2), December 2006
3. Landsberg, H.E., 1970. Climates and urban planning. WMO Tech. Note No. 108.
4. Mohapatra, M., 2002. Recent trends in climate of Bangalore, Mausam, 53(4): 425-438.
5. Murthy, B.P., 1979. Isothermal and isotherms in Pune on clear winter nights. A Met. Study. Mausam, 30: 473-478.
6. Murthy, B.P., 1999. Hot cities in hot climate. WMO Int. Conf. on Urban Climatology, Sydney.
7. Oke, T.R., 1974. Review of urban climatology 1968- 73. WMO Tech.Note 134, WMO No. 383, Geneva.
8. Oke, T.R., 1979. Review of urban climatology 1973- 76. WMO Tech. Note 169, WMO No. 539, Geneva.
9. Philip, Daniel and Murthy, K., 1974. Seasonal variation of surface temperature distribution over Bombay. Proc. Symp. Environ. Pollution, Nagpur.
10. Price, J., 1979. Assessment of the urban heat island effect through the use of a satellite data. Mon. Wea. Rev., 107: 1554-1557.
11. Rao G.S.P., Jaswal A.K., & De, U.S., 2000. Extreme temperature events in India, Proceedings of Tropmet-2000, 1-4 Feb., Kochi (India).
12. Rupakumar, K., Krishnakumar, K., & Pant, G.B., 1994. Diurnal asymmetry of surface temperature trends over India. Geophys.Res.Lett.21: 677-680.
13. Shende, R.R., & Gaikwad, A.N., 2003. Major inorganic ion composition of rainwater at some GAW (BAPMON) stations in India. Mausam 54 (3): 763-787. 14. U.S.De and G.S.Prakasa Rao., 2004. Urban Trends – The Indian Scenario. J.Ind.Geography.Union (July2004), Vol.8, No.3: 199-203
15. WMO, 1989. Proc. of Int. Conf. on Urban Climate, Planning and Building, Kyoto, Japan. 16. WMO, 1999. Proc. of Int. Conf. on Urban Climatology, Sydney, Australia
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