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Inter-annual and Seasonal Variations of Surface Air Temperature of Major Cities in Bangladesh

Nazlee Ferdousi
SAARC Meteorological research Centre (SMRC), Dhaka, Bangladesh

Md. Mizanur Rahman
SAARC Meteorological research Centre (SMRC), Dhaka, Bangladesh

Abstract/ Executive Summary:

The present study investigated recent trends in the mean annual maximum and minimum surface air temperature at selected six major cities over Bangladesh by using statistical techniques. Annual and seasonal records of maximum and minimum surface air temperature of major cities for the period 1971-2011 were used in this analysis. The cities are Rajshahi, Sylhet, Dhaka, Khulna, Barisal and Chittagong. The trend of mean annual maximum and minimum surface air temperature has been analyzed using linear regression technique, which showed that the warming trend is dominant over the city areas in Bangladesh. It has been found that at Sylhet, Barisal, Chittagong and Dhaka the temperature shows very strong warming trends of maximum temperature with high values of 0.048^o, 0.026^o, 0.024^o and 0.022^oC/year. These cities also show strong warming trends of minimum temperature.

The values of seasonal mean maximum and minimum surface air temperatures in the cities were computed for winter (December–February), pre-monsoon (March-May), monsoon (June-September) and post-monsoon (October-November) seasons. The seasonal mean maximum and minimum surface air temperature show increasing trends except Rajshahi (-0.015^oC/year) for minimum temperature in post-monsoon. Rajshahi also shows decreasing (cooling) trend in the winter season of -0.011^oC

Keywords: Inter-annual variation, Linear trend, Statistical techniques, Surface Air Temperature.

Location: Rajshahi, Sylhet, Dhaka, Khulna, Barisal and Chittagong.

Start Date: 00-00-1971

End Date: 00-00-2011

Program Area: Resource Development and Management

Commodity: Temperature

Objectives:

Considering the above, in the present paper, the study has been carried out on the recent annual and seasonal climate variability and its trends using the data of maximum and minimum surface air temperatures in Bangladesh.

Methodology:

The maximum and minimum surface air temperatures for individual years and seasons (winter, pre-monsoon, monsoon and post-monsoon) have been estimated from the monthly data. The data period of temperature was used from 1971 to 2011 but for Khulna city minimum temperature was used from 1981 to 2011. The interannual variability and linear trends have been analyzed using the temporal plots of these parameters and least square regression analysis. The significance levels of the slopes of the linear trends have been calculated using the student t-test.

Source of Information: Journal of Engineering Science 05(1), 2014, 91-97

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

On the basis of the present study, the following conclusion can be drawn: i. The mean maximum surface air temperature shows strong warming trend over all selected major cities in Bangladesh for the period 1971-2011. Among the major cities temperature shows a higher warming trend at Sylhet and lower warming temperature at Khulna with the values of 0.048^oC/year and 0.015^oC/year respectively which are statistically significant at 1% and 5% level respectively. The causes of the warming are attributed mainly to the radiative forcing due to the increased greenhouse gases. Besides, the local changes such as urbanization, land-use changes and industrialization have impacts on the local changes of the thermal regime. Very strong warming in the cities at Sylhet, Barisal, Chittagong, Dhaka and Rajshahi at the rate of 0.049^oC/year, 0.026^oC/year, 0.025^oC/year, 0.022^oC/year and 0.019^oC/year respectively is due to the rapidly expanding urbanization in these cities areas. ii. Strong warming trends of mean maximum surface air temperature is observed in all the seasons except the winter seasons where the increasing trend is very week except at Sylhet and Chittagong. Sylhet and Chittagong shows warming trend at the rate of 0.045^oC/year and 0.038^oC/year respectively which are statistically significant at 1% level and decreasing trend is also observed at Dhaka and Rajshahi cities at the rate of -0.0002^oC/year and -0.012^oC/year respectively, which are not statically significant. iii. The mean minimum surface air temperature during the study period 1971-2011 shows the strong(highest) warming trends of 0.040^oC/year and 0.037^oC/year at Khulna (data was used from 1981- 2011) and Sylhet respectively, which is statistically significant at 1% level and lowest of 0.001^oC/year at Rajshahi which is not statistically significant. iv. The seasonal mean minimum surface air temperature of major cities for all four seasons shows increasing trends except Rajshahi and Chittagong. Rajshahi city has been found decreasing trends at the rate of -0.011^oC/year and -0.015^oC/year for winter and post-monsoon seasons and Chittagong city has also been found almost neutral trend (0.005^oC/year) for the post-monsoon season. These are not statistically significant. Very strong warming trends are exhibited at Khulna and Dhaka with high values of 0.058^oC/year and 0.055^oC/year for the winter season, which are statistically significant.

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