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Trend of Rainfall and Temperature in Different Regions of Bangladesh During the Last Five Decades

Dr. M. H. Ali
SSO
BINA

A.K.M.R. Islam
Assist. Prof.
GTI, BAU

M.G.M. Amin
Assist. Prof.
IWM, BAU

Abstract/ Executive Summary:

Time series of yearly and monthly rainfall, and monthly maximum and minimum temperatures at five stations covering different regions of Bangladesh were investigated for temporal and spatial trends. The study reveals no significant trend in annual rainfall. Significant decreasing trend of monthly rainfall during monsoon (wet season) at two stations and increasing trend during dry season at several stations are observed. Time series of monthly maximum and minimum temperatures appear to follow some trends, showing increase and decrease at two extremes, respectively. Time series of minimum temperature showed inconsistent trends throughout the year and also between stations.

Keywords: Rainfall variability, Climate change, Monsoon, Agricultural practice, Bangladesh

Location: Mymensingh, Rangpur, Rajshahi, Khulna and Chittagong

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Non-commodity: Temperature, Rainfall

Objectives:

The main objectives of this study are to investigate the trend of: (i) yearly and monthly total rainfall, (ii) monthly maximum and minimum temperature over different regions of Bangladesh.

Methodology:

Five meteorological stations, were selected for study. The stations were: Mymensingh, Rangpur, Rajshahi, Khulna and Chittagong. The climatic data (monthly maximum/minimum temperature, and monthly total rainfall) from 1948 to 2001 were collected from Bangladesh Meteorological Department. Trends of yearly rainfall, monthly rainfall, monthly maximum temperature, and monthly minimum temperature were investigated by non-parametric as well regression (slope) method.

Trends were examined by ‘Spearman’s Rho’ test (Conover, 1980). The test statistic T of ‘Spearman’s Rho’ test is given by:

where X_i is the value of rainfall (or temperature) corresponding to the year Y_i, R(X_i) is the rank of rainfall (or temperature) X_i, and R(Y_i) is the rank of the year Y_i_.For n greater than 30, the quantiles of T is approximated by (Conover, 1980):

where x_p is the pth quantile of a standard normal random variable. Upper quantile was estimated from the equation:

In all cases, the two tailed test was done at level α = 0.05 .

Trend was also examined by testing the significance of slope of the linear regression line. For this purpose, climatic variables were plotted (Y-axis) against the relative year values (year rank, i.e. for 1948 to 2001, relative year values are 1 to 54). The slope of the plot represents the trend. The slope was then subjected to t-test for significance at 5 % level.

Source of Information: J. Agrometeorol.,9(1): 26-33, 2007

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The following conclusions can be made from the present study: There is no significant trend in yearly rainfall at different locations over 54 years data. Monthly rainfall indicates a change in pattern of rainfall, although it is not significant in most cases. Monthly maximum and minimum temperatures show trend in time series, showing warming and cooling at two extremes, respectively. Uncertainties of relating temperature to rainfall are exhibited.

Knowledge Management: Journal