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Trend Analysis and Spatial Distribution of Monsoon Precipitation Over Bangladesh During 1951-2012

S. M. Quamrul Hassan
Bangladesh Meteorological Department, Agargaon, Dhaka-1207, Bangladesh

M. A. K. Mallik
Bangladesh Meteorological Department, Agargaon, Dhaka-1207, Bangladesh

Md. A. E. Akhter
Khulna University of Engineering & Technology

M. A. M. Chowdhury
Department of Physics, Jahangirnagar University, Savar, Dhaka, Bangladesh

Abstract/ Executive Summary:

In this study monthly rainfall data for 12 stations over Bangladesh for the period 1951-2012 are used to investigate and understand the inter-annual variability of the summer monsoon rainfall. Monthly, seasonal, and annual spatial rainfall patterns, and the spatial patterns of variability, are presented. Rainfall was found decreasing in the months of June, July and August but it was increasing in September. The trend of the country averaged monsoon rainfall was slightly decreasing during this period. Large spatial variation of the rate of change of monsoon rainfall was found over Bangladesh. The analysis of the decadal mean monsoon rainfall shows that the decades 1951-1960, 1961-1970 and 1981-1990 were wet i.e. rainfall was above normal and the decades 1971-1980, 1991-2000 and 2001-2010 were dry i.e. rainfall was below normal.

Keywords: Rainfall trends, Variability, Monsoon

Location: In Bangladesh

Start Date: 00-00-1951

End Date: 00-00-2012

Program Area: Resource Development and Management

Commodity: Precipitation, Trend analysis

Objectives:

The onset and withdrawal dates of the summer monsoon in Bangladesh vary from year to year. The summer monsoon generally begins over the southeastern part of Bangladesh by late May or early June and withdraws by the middle of October. Detailed work on the onset and withdrawal dates of summer monsoon over Bangladesh has been done by Ahmed and Karmakar (1993). As per their study, the mean onset dates of summer monsoon in Bangladesh in the extreme south-eastern coastal part and in the extreme north-western part are 2 June and 15 June respectively. The present study focuses on the spatial and intra-seasonal variability and trends of summer monsoon rainfall in more detail over Bangladesh by using the available long period dataset 1951-2012.

Methodology:

DATA USED In this study the observed daily and monthly rainfall data of 12 selected rain gauge stations of Bangladesh during the period 1951-2012 (62 years) were collected from the Bangladesh Meteorological Department (BMD). The stations are selected on the basis of the availability of maximum data length and data accuracy. There were some missing data that were filled up by 30 years average. For filling up missing data WinSurfer software was used by using the Kriging method. The monthly and seasonal rainfall data are constructed on the basis of the daily rainfall data.

In this study for data query Office Access version 10 has been used, for calculation and making graph MS-Excel version 10 has been used. For spatial analysis, WinSurfer version 10 has been used.

Source of Information: Journal of Engineering Science 06(1&2), 2015, 75-80

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

1. The long-term mean of the monsoon rainfall over Bangladesh during the period of 1951-2012 is 1602 mm (about 13 mm/day) and the standard deviation for this period is 206 mm (about 1.7 mm/day). 2. During the period 1951-2012, there have been 15 occasions when monsoon rainfall was deficient (below -10% of normal rainfall) and 15 occasions when the monsoon rainfall was excess (above 10% of normal rainfall). 3. Trend of the country averaged monsoon rainfall has a slightly decreasing trend at the rate of (-0.057 mm/year). There is a decreasing trend of rainfall in the months of June, July and August but it has an increasing trend in the month of September. The standard deviation of the monsoon rainfall anomalies indicates large variability at Comilla and Khulna region have large variability but less variability at Chittagong and Sylhet region. 4. There is a large spatial variation of the rate of change of monsoon rainfall over Bangladesh. The highest decreasing rate of rainfall is found over the Comilla region and the highest increasing rate is found over the Khulna region. 5. The decades 1961-1970 and 1981-1990 were wet and the decades 1971-1980, 1991-2000 and 2001- 2010 were dry.

Knowledge Management: Journal