Abstract
A study was carried out to analyze the rainfall data for crop planning in rainfed regions,, Probability analysis of rainfall offers a better scope for predicting the minimum assured rainfall to help in crop planning. The 75% probability of rainfall occurrence was proposed as an index of dependable rainfall for crop production. Considering this in view, 25 years (1981-2005) of rainfall data of Mymensingh district have been analyzed in greater details covering probability aspects. Assured rainfall analysis, probability of potential evapotranspiration, water-balance approach and actual evapotranspiration were found quite effective to assess the water availability period for crop planning under rainfed condition. It was found that maximum rainfall occurred in July and minimum in December. The numbers of rainy days per year at 75% probability were 128 days. In the month of July and August numbers of rainy days were 20 and in December, it reduced to zero. The highest potential evapotranspiration was obtained in April (4.6 mm/day) and the lowest in January (2.4 mm/day).It was observed that April to October is the rainfall excess (rainfall>PET) and November to March is the deficit period (PET>rainfall). Climatic water balance revealed the possibility of water harvesting during May to October. It may be concluded that probabilistic rainfall data and number of rainy days, would be quite helpful for crop planning. It provides useful information like land preparation, planting, transplanting, intercultural operations, harvesting, threshing, drying and other cropping practices. This would go a long way in crop planning at farmers and at policy making level. DOI: http://dx.doi.org/10.3329/jbau.v11i2.19935 J. Bangladesh Agril. Univ. 11(2): 313-320, 2013
Highlights
The uneven distribution of rainfall of Bangladesh sometimes creates unfavorable conditions for crop growth and agricultural droughts of varying intensities limit the crop production potential
Analysis of rainfall in Mymensingh districts revealed that 85% (Table 1) of the total average annual rainfall occurred during the monsoon period (April to October), and the remaining 15% were distributed in the pre-monsoon and post-monsoon periods, respectively
About 70% of the annual rainfall occurred during the months of June to September and 90% during May to October
Summary
The uneven distribution of rainfall of Bangladesh sometimes creates unfavorable conditions for crop growth and agricultural droughts of varying intensities limit the crop production potential. Ali et al (1994) found that the average annual rainfall in the country was 2486 mm They found that the average monsoon rainfall in every year was 66.76% of the total rainfall in the year. Fluctuations in the monsoon alone attribute approximately 30% variation in the grain production (BBS, 2004).In Bangladesh work on rainfall for crop planning has been done by many workers. Little work has been done in Mymensingh on probability studies of rainfall for Agricultural planning. The parameters such as amount, intensity, spread of rainfall and number of rainy days are being used to characterize rainfall in a place. Rainfall prediction can help farmers in determining best adapted plant species, the optimum time of ploughing and seeding, planning supplemental irrigation schemes, evaluation of alternative cropping and soil-water management plans and selection of harvesting time
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