Urban influences on selected climatic parameters in Dhaka metropolitan area

Abstract

In this study, efforts have been made to study the effect of urbanization on selected climatic parameters such as rainfall, surface temperature 'and atmospheric pressure for Dhaka metropolitan area. The development of Dhaka metropolis was very rapid between the 70's and 90' s of this century. Dhaka city is often criticized as the city of unplanned growth, which if continued would have adverse effects on the environment and economy. An understanding of the changes in the magnitude of rainfall, surface temperature and atmospheric pressure due to increased urbanization is essential for proper land use planning and checking unplanned growth of metropolitan area. Mymensingh and Tangail have been chosen together with Dhaka city to compare the changes of climatic parameters between less urban area and a highly urban area. The annual and seasonal data were studied for the period from 1953 to 1995 for Dhaka, 1951 to 1995 for Mymensingh and 1962 to 1995 for Tangail. The data required for this study are daily values of rainfall, maximum temperature, minimum temperature and atmospheric pressure. Changing trends of summer, monsoon and annual data senes of rainfall for Dhaka show different patterns from that of less urban area i.e. Mymensingh and Tangail. Annual rainfall and monsoon rainfall of Dhaka does not show any significantly increasing or decreasing trend; only the pre-monsoon rainfall shows a linearly increasing trend. One day annual maximum rainfall and the number of monsoon rainy days for Dhaka exhibit a significantly decreasing trend. Whereas, these data series of rainfall for Mymensingh and Tangail show a significantly increasing trend. Coefficient of variation of mean monthly rainfall is less in Dhaka than the other two less urban stations. Significantly decreasing trend of coefficient of variation of annual rainfall for Dhaka and Tangail provides the evidence that the increase in the rainfall variability is occurring at a slower rate, and this rate of decreasing tendency is more in Dhaka than Tangail. The decreasing trend of coefficient of variation of annual rainfall for Mymensingh is not significant Surface temperature in Dhaka, a rapidly growing urban area, exhibits an increasing trend during the last two to three decades compared to less urban area. Significant urban heating effects have apparently taken place in Dhaka, as urban-affected temperature increase of O.75°C to 1.15°C over 43-year period have been found in this study. In contrast, temperature for less