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Trend of Monsoon Rainfall Pattern in Bangladesh

Mohammad Rezaur Rahman
Institute of Flood Control and Drainage Research, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh

Mashfiques Salehin
Institute of Flood Control and Drainage Research, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh

Jun Matsumoto
Department of Geography, University of Tokyo, Tokyo 113, Japan

Abstract/ Executive Summary:

Monsoon is a very important component of the climate of Bangladesh. Whether monsoon is being or will be affected by global warming has become a concern of environmentalists. Any change in monsoon climate will have significant bearing in Bangladesh as flood in Bangladesh is heavily dependent on monsoon rainfall. In this study long term trend of rainfall using data for the period of 1860-1991 at selected stations of Bangladesh for each month of monsoon has been investigated. Analyses show that although a few stations show evidences of a changing pattern of rainfall, overall it can be said that there is no conclusive evidence to suggest any changing pattern of monsoon rainfall.

Keywords: Rainfall, Monsoon rainfall, Climate, Global warming

Location: Institute of Flood Control and Drainage Research, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh

Start Date: 00-00-1960

End Date: 00-00-1991

Program Area: Socio-economic and Policy

Non-commodity: Rainfall

Objectives:

The objective of this paper was to investigate whether there exists any discernible trend in rainfall during different time periods within monsoon in selected stations of Bangladesh.

Methodology:

In this paper a month was taken as a period. Monsoon has been defined as the period between June to September. Therefore there are four periods (June, July, August, September) within each monsoon. In this study, monthly rainfall data for the period of 1860 to 1991 were used. The monthly rainfall data for the period of 1860 to 1946 were obtained from Indian Meteorological Department. The data from 1948 to 1991 were obtained from Bangladesh Meteorological Department. In this study a total of twelve stations representing different regions of Bangladesh were selected for analysis. There are some missing data, number of years of missing data for each station. It is seen that the missing length of data is considerably less compared to available length of data. So, no special treatment for missing data was made in this study. The trend analysis was done using a non-parametric test namely Mann-Kendall test. The advantage of the non-parametric test is that it does not depend on absolute values of data and is equally applicable for linear and non-linear trend. The test is reproduced here from Maidment (1992). Let the annual series be y_t, t = 1 ... N. Each value Y_t', t'=1, .... . N - 1 is compared with all subsequent values y_t, t = t' + 1, t' + 2, .... N, and a new series Z_k is generated by Z_k = 1 if y_t > y_t', Z_k = 0 . if y_t = y_t', Z_k = -1 if y_t < y_t', In which k = (t' - 1) (2N - t') / 2 + [t-t']. The Mann-Kendall statistic is given by the sum of the Z_k series. This statistic represents the number of positive differences minus the number of negative differences for all the differences considered.

Source of Information: Bangladesh Journal of Water Resource Research, Vol. 14-18, 1997

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Long term trend of monsoon rainfall was investigated in this study. The results indicated that there is no discernible change in total monsoon rainfall. Although Chittagong showed a changing pattern of rainfall, the overall evidences do not suggest any changing pattern of monsoon rainfall within Bangladesh. This finding is similar in line with findings of studies that have been carried out for India which has similar climatic features like Bangladesh. Therefore, it can be concluded that any observed recent warming of global mean temperature has little effects upon rainfall' regimes over South Asian monsoon rainfall, as far as monthly or seasonal amount is concerned. However, further study is needed to investigate if there is any trend in other rainfall characteristics, such as rainfall intensity or duration of rainfall.

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