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Gamma Distribution and Its Application of Spatially Monitoring Meteorological Drought in BARInd, Bangladesh

A. T. M. J. Alam
Department of Environmental Sciences, Jahangirnagar University, Dhaka, Bangladesh

M. M. Huq
Department of Statistics, University of Rajshahi, Rajshahi, Bangladesh

H. M. Saadat
Department of Environmental Sciences, Jahangirnagar University, Dhaka, Bangladesh

M. S. Rahman
Department of Statistics, University of Rajshahi, Rajshahi, Bangladesh

Abstract/ Executive Summary:

The Barind tract of Bangladesh suffers from frequent drought due to erratic rainfall distribution. In the present study details analysis of rainfall data has been carried out for the years 1971-2010. The Standardized Precipitation Index (SPI) which is followed by gamma distribution is used to evaluate drought vulnerability based on frequency and severity of drought events at multiple time steps (3, 5 and 12 months). Drought severity maps are generated in a GIS (Geographical Information System) environment using inverse distance weighting method. Critical (threshold) rainfall values are derived for each station at multiple-time steps in varying drought categories to determine least amount of rainfall required to avoid from drought initiation. The study found that drought vulnerability portrays a very diverse but consistent picture with varying time steps. Analysis and interpretation of the map shows a similar spatial distribution of drought in pre-monsoon season but in monsoon season rainfall deficits shifts its position time to time and occurred in certain discrete pockets. In 12 months period the spatial distribution of drought was almost similar with monsoon season. In pre-monsoon season drought severity was higher in north eastern part of the study area compare to other parts. The study also evident that critical threshold values of rainfall to avoid drought condition was higher in the northern part of high Barind than southern part.

Keywords: Barind tract, Drought, Gamma distribution, GIS, Spatial analysis, SPI

Location: Barind tract of Bangladesh

Start Date: 00-00-1971

End Date: 00-12-2010

Program Area: Risk Management in Agriculture

Non-commodity: Impact

Objectives:

1. The study also identifies annual and seasonal critical or threshold value of rainfall that is requires avoiding drought condition. The identified critical value of rainfall can be utilized as a planning period for mitigating the impacts of meteorological drought that manifests as a result of rainfall shortages in the area.

Methodology:

It is proposed Standardized Precipitation Index to assess anomalous and extreme precipitation. Since precipitation data are mostly skewed, in order to compute SPI, precipitation data are normalized using gamma function. SPI is based on the probability of precipitation for any desired time scale. In order to compute SPI, historical rainfall data at each station are fitted to gamma probability distribution function.

Source of Information: J. Environ. Sci. & Natural Resources, 5(2): 287 - 293, 2012; ISSN 1999-7361

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The study found that monsoon and yearly drought follow almost a similar spatial distribution in the same year but the magnitude and frequency of drought varies year to year in some discrete pockets. On the other hand pre monsoon drought is focused mostly on the north western corner with higher magnitude. Critical analysis of rainfall also suggests that the area is vulnerable to future chronic drought event. Moreover, it is require higher amount of rainfall in the northern part of the study area to avoid drought.

Knowledge Management: Journal