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Probability Analysis of Monsoon and Off-monsoon Rainfall and Crop Planning in Bangladesh

Dr. M. H. Ali
SSO
BINA

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

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

Abstract/ Executive Summary:

Rainfall is the single-most important climatic parameter influencing agriculture. Agriculture in Bangladesh has developed over the centuries to accommodate and take advantage of monsoon rainfall. Information on variability of monthly rainfall is required in many areas of water resource management and engineering design, selecting areas for profitable rainfed farming and developing possible means for rainwater harvesting during monsoon season. It may also help in identification of appropriate crops and cropping sequences that can match the water-availability duration and ensure increased and stabilized crop production. Monthly rainfall for six selected stations (covering different regions of the country) for the period from 1948 to 2001 are analyzed in a greater details covering probability aspects. The rainfall analysis suggest that at different regions of Bangladesh, cropping during dry period (No.-March) can easily be adopted by proper selection of crops and varieties for increasing cropping intensity under rainfed cultivation.

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

Location: Throughout the country.

Start Date: 00-00-1984

End Date: 00-00-2001

Program Area: Risk Management in Agriculture

Commodity: Rice

Objectives:

Analysis of monsoon and off-monsoon rainfall with a view to assist in proper crop planning in Bangladesh.

Methodology:

Site description and data collection

Six different stations (Mymensingh, Pabna, Rajshahi, Comilla, Rangpur, Khulna) located at different representative regions (and agro-ecological zones) of the country were selected for study. Monthly mean data of rainfall, for the period from 1948 to 2001 were collected from Bangladesh Meteorological Department.

Probability analysis

Weibull’s ranking method was used to find the probability of a certain event. According to this method, yearly data were arranged in descending order for probabilities of exceedance. The probability, P, was calculated as follows: P = m /( N+1) .......................... ( 1 )

Where, N = number of records, m = rank number.

The probabilities thus found were plotted on log-normal probability paper. The points were found to approximate a straight line which indicated in all cases that the distribution is approximately log-normal. Then year value at 80 % probability (P80) was selected. The P80 represents the dry year. Deficit period was assessed from the graph of period of the year vs. rainfall and potential evapotranspiration (PET).

Calculation of potential evapotranspiration

Potential evapotranspiration (PET) was calculated by FAO ‘CROPWAT’ software (Windows version 4.2 ) using historical weather data.

Deficit was calculated as: Deficit = 0.3 ET – P80

Source of Information: Ali, M.H., M.G.M. Amin and A.K.M.R. Islam (2005). Probability analysis of monsoon and off-monsoon rainfall and crop planning in Bangladesh. Bnagladesh J. Env. Sci., 11(2): 290 - 295

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The rainfall analysis suggest that at different regions of Bangladesh, cropping during dry period (No.-March) can easily be adopted by proper selection of crops and varieties for increasing cropping intensity under rainfed cultivation.

Knowledge Management: Journal