Spatio - temporal assessment of drought patterns in Bangladesh

Abstract

Recently the frequency and intensity of drought conditions have been increased throughout Bangladesh. As the agricultural activities of the country are still very much dependent on nature especially on seasonal rainfall, shortage of rainfall found during dry periods has adverse impact on agriculture as well as the economy of the country. Intensified drought damages have increased the urgency of proper assessment of drought in Bangladesh. There is no unique method for the assessment of drought and the study on drought assessment in Bangladesh is very few. Within the constraints of necessary data, this study has been performed to propose several methods to characterize; assess; quantify meteorological drought severity and damage; and prioritize potential adaptation measures against drought in Bangladesh. Two principal meteorological parameters, rainfall and temperature have been used in this study to assess drought scenario of Bangladesh. Drought condition has been defined and seasonal dryness maps have been proposed for identification of dryness well as drought area throughout the country. In this study, discrete as well as cumulative rainfall anomaly, Rainfall Anomaly Index etc have been used to characterize drought scenario in Bangladesh. Again, spatio-temporal variations of seasonal rainfall intensity, Drought Area Index, Drought Severity Index etc have been used to quantify drought in the country. Drought potential also has been assessed by Stochastic (Random) Component Time Series analysis and analyses on upper confidence level of temperature and lower confidence level of rainfall. Again, drought damage cause factors have been proposed in this study. Based on the proposed methods, the driest pre-monsoon has been found in Madaripur due to decrease of rainfall of 9.61 mm/year. Comilla has got the driest monsoon and post-monsoon having the rainfall decrease of 12.41 mm/year and 1.48 mm/year respectively. The driest winter has been found in Tangail where the rainfall decrease is 2.20 mm/year. Again, Dinajpur and Chuadanga have been found in the worst condition of dryness and prone to drought from the consideration of developed dryness slopes. Analyses on rainfall anomalies show that extended drought periods have been returned during 2002 – 2008 after the period of 1953 – 1963 in Dhaka. Maximum decrease in monsoon rainfall has been found in Comilla at the rate of 0.006 mm/hr. The ranges of rainfall intensity for drought condition have been found as 0.00-0.29 mm/her in pre-monsoon, 0.00-0.45 mm/hr in monsoon, 0.00-0.17 mm/hr in post-monsoon and 0.00-0.03 mm/hr in winter. Percentage of seasonal rainfall anomaly shows that percentage of dry year is the maximum (42%) in Jessore, while it is 38% in Dhaka. Stochastic Component Time Series (SCTS) analysis presents that the probability of high drought is the highest in Comilla (61%) and the lowest in Dinajpur (2%). Drought damage cause factors are the minimum during the wet periods whereas these are the maximum during dry periods. In Dhaka, the minimum damage cause factor has been found as 0.02 °C/mm.month during monsoon, whereas the maximum has been got as 5.46 °C/mm.month during winter. This study presents some recommendations for future scope of research on drought in Bangladesh.