Study of Rainfall & Temperature Trend in Bangladesh

Abstract

Climatic data collected from Bangladesh Meteorological Department was used for the study. The regression equation, the coefficient of determination, standard deviation and coefficient of variation were calculated for the analysis. Mann-Kendall test for trend and Sen’s slope estimates were also calculated. Annual average temperature (Tavg) in all division is increasing. The Tavg in Khulna is increasing by 0.007ºC/year, in Dhaka it is increasing by 0.021ºC/year. The average temperature has also an increasing trend in other divisionsand the rates are 0.0110C/year in Rajshahi, 0.019ºC/year in Sylhet, 0.0001ºC/year in Rangpur, 0.013ºC/year in Chittagong, 0.012ºC/year in Barisal and 0.003ºC/year in Mymensingh.Annual maximum temperature (Tmax)has an increasing trend in Khulna, Dhaka, Rajshahi, Sylhet, Barisal and Chittagong divisions while it has decreasing trend in Rangpur and Mymensingh divisions. The Tmax in Khulna is increasing by 0.01 ºC/year, in Dhaka it is increasing by 0.0179 ºC/year. And the maximum temperaturehas also an increasing trend in Rajshahi, Sylhet, Chittagong and Barisal divisions.The rates of increase are 0.006 ºC/year in Rajshahi, 0.018 ºC/year in Sylhet, 0.020 ºC/year in Chittagong and 0.0178 ºC /year in Barisal divisions. Whereas the maximum temperature has a decreasing trendat -0.014 ºC/year and -0.004 ºC/year in Rangpur and Mymensingh divisions respectively. Annual minimum temperatures (Tmin) in all divisions areincreasing.The Tmin in Khulna is increasing by 0.0058 ºC/year, in Dhaka it is increasing by 0.024 ºC/year. The minimum temperature has also an increasing trend in other divisions and the rates are 0.016 ºC/year in Rajshahi, 0.021ºC/year in Sylhet, 0.015 ºC/year in Rangpur, 0.007 ºC/year in Chittagong, 0.006 ºC/year in Barisal and 0.010 ºC/year in Mymensingh. The Mann- Kendall test indicates that in Khulna division Tavg has an increasing trend in monsoon and post monsoon seasons with value of Z 6.31and 2.52 which are statistically significant. This test also indicates that in Dhaka division,it has an increasing trend in pre-monsoon, monsoon, post monsoonand winter seasons with value of Z 2.75, 6.23, 5.60 and4.62 respectively which are statistically significant. In Rajshahi division, it has an increasing trend in monsoon season with value of Z 6.25which is statistically significant.In Sylhet division, it has an increasing trend inpre-monsoon, monsoon, post monsoonand winter seasons with Z values of 2.24,6.10, 5.24 and4.60 respectively which are statistically significant.In Rangpur division, it has an increasing trend in monsoon while decreasing trend in winterseasons with valuesZ of 3.85 and -1.86 which are statistically significant. In Barisal division,it has an increasing trend in Monsoon and Postmonsoon seasons with Z values of are 4.77 and 3.48 which is statistically significant. In Chittagong division, it has an increasing trend in pre-monsoon, monsoon, post-monsoonand winter seasons with Z values of 2.25,6.44,3.94and 1.79respectively which are statistically significant.In Mymensingh division,it has an increasing trend inmonsoon season with Z value of 5.11 which is statistically significant. Annual total rainfall has an increasing trend in Khulna, Rajshahi, Sylhet, Chittagong, Rangpur and Mymensingh divisionswhile decreasing trend in Dhaka and Barisaldivisions. The total rainfall has an increasing trend in Khulna by 3.392 mm/year, in Rajshahi it is increasing by 2.3279 mm/year. The total rainfall has also an increasing trend in Sylhet, Rangpur, Chittagong and Mymensingh divisions. The rates are 2.6605 mm/year in Sylhet, 5.5885 mm/year in Rangpur, 1.889 mm/year in Chittagong and 2.283 mm/year in Mymensingh division. Whereas the total rainfall has a decreasing trends (-2.0292 mm/year) in Dhaka and (-1.985 mm/year) in Barisal division. The results suggest that temperature and rainfall are increasing in most of the stations and divisions.