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.
