Characterization of 1994-95 drought in north western region of Bangladesh and its impact on agriculture

Abstract

This study involves meteorological characterization of drought and water deficit in north western region. Estimation of crop yield and income losses for 1994-95, together with an assessment of shortage of drinking water and increase in disease incidences are also investigated through questionnaire survey. The daily rainfall records of 35 sites in the north-western region of Bangladesh and three evaporation stations are used for this study. The analysis involves whether the selected rainfall series from a number of measuring sites of a region are discordant and determining the different sequential property with a view to apply simple analytical solutions to various problems related to stochastic behavior of wet and dry spells of rainfall sequences. The discordancy measure identifies no unusual sites. The daily rainfall record of monsoon period are persistenct in nature whereas in the premonsoon it is devoid of persistency. The persistent behavior of wet and dry spells are modeled by Markov (order 1) process using the theory of runs. As such, to build the model blocks, Poisson probability density function of the occurrence of spells is coupled with geometric distribution for the length of spells and the Weibull, normal, lognormal and gamma distributions for the total rain of wet spells. Random model appears to be a poor simulator and Markov model inferred as a promising one. Longest wet and dry periods are obtained by Markov model and largest rain-sum by Markov-Weibull model. Contour maps of longest dry or wet spells and largest rain-sum at different probability are drawn to identify the regional variation characteristics. The maximum longest dry spell is at lower part of Dinajpur and Rangpur districts which is 12-13 days at 50 perecnt probability and 19-20 days at 90 percent probability while the largest rain-sum (Sm) is at upper part consisting of Panchagarh, Nilphamari, Lalmonirhat and Kurigram which is about 350-450 mm at 50 percent probability while at 90 percent is 650-750 mm. The maxirimm longest wet spell (Lwm) is at upper part of Rangpur, Kurigram, Lalmonirhat and Parichagarh. II Water availability and la-day water deficit (i.e. demand) is calculated for the period of record 1976-96. 1994-95 has the higher deviation of 1132 mm from the average rainfall. Extreme value type 1 (EVl) distribution is fitted to la-day maxima for each station. Overall, EVI distribution seems to fit the demand well. To make an estimate of the agricultural damages, socio-economic and environmental impact, data related to these parameters are collected through questionnaire survey in Badarganj and Kishoreganj areas. Production and income losses are 30 and 60 percent respectively at Badarganj whereas at Kishoreganj it appears 15 and 25 percent. Badraganj is more severely affected area than Kishoreganj. In 1994-95 Boro and Aman crops were affected more than other crops. During the drought period there is no doubt about the increase of temperature and dust compared to normal years. Decline in water table below normal levels are also estimated. It has been observed that in 1994-95 groundwater level is about 2 m below than the other years.