Key Climatic Perils and Crop-Area Damage Assessment
This section presents an analysis of BBS great district or regional level crop-damage statistics by cause of loss (including flood, flash flood, cyclone, hailstorm, and tornado) for paddy crops cultivated in Bangladesh for the 16-year period 1990–91 to 2005–06. This analysis is useful to provide a macrolevel assessment of the relative exposure to and damage levels associated with each type of climatic or natural peril.
Key Climatic Perils
The geographical setting of Bangladesh makes the country very vulnerable to natural disasters. The country is ranked fifth out of 204 countries on the Natural Disaster Index. The major disasters affecting the agricultural sector in Bangladesh are the occurrences of river floods, flash floods, droughts, cyclones and storm surges, and tornadoes, and hailstorm. Map 3.4. shows the geographical distribution of the vulnerability to different natural hazards in Bangladesh.
River floods are a recurrent phenomenon in Bangladesh. The central and northeastern areas of the country are particularly prone to flood due to drainage congestion. Approximately 20 percent of the territory is normally flooded every year. However, abnormal floods affecting 37, 43, 52, and 60 percent of the territory are expected to occur with return periods of 10, 20, and 50 and 100 years, respectively (MFDM, 2006). The floods of 1988 and 1998 were particularly catastrophic for the country and for the agricultural sector. The normal flood period occurs between April to October, with the most severe events during the months of July to August.
Flash floods are a recurrent feature in the mountainous areas of the northeast and eastern Bangladesh. Flash floods can be defined as the sudden-onset floods caused by heavy and sustained rainfall. This type of flood normally takes place during the premonsoon season, from April to May. The occurrence of early flash floods can be extremely prejudicial to boro paddy as they coincides with the time of harvest. The most vulnerable regions are located in the northern and eastern part of the country.
Drought conditions due to rainfall deficit affect different parts of Bangladesh mostly during the premonsoon and postmonsoon periods. Out of the 55-year period from 1949 to 2007, 11 drought events occurred in Bangladesh. The worst drought in recent history occurred in 1979 affecting 42 percent of the territory. Dry spells or crop droughts, in particular between April to July, are common and can result in enormous suffering for the poor, especially for those depending on rainfed, subsistence farming. Drought in Bangladesh mainly affects the western part of the country, in particular the Barind Track region.
Cyclones affect the coastal Districts of Bangladesh, causing immense damage to the agriculture sector. Cyclones usually take place during premonsoon (April to May) and postmonsoon (September to November.) periods. The cyclone tracks, once they make landfall in Bangladesh, move northeastwards. The heavy rains accompanying cyclones and the wind-effect rise in tides, called storm surges, cause most of the damages in the agricultural sector. An average of one to three severe to moderate cyclonic storms hit Bangladesh each year, with associated storm surges as much as 13 meters higher than normal that in extreme cases can reach as far as 200 kilometers inland (Milliman et al. 1989). Storm surges of 4, 4.7, 5.4, and 6.4 meters above the normal sea level are expected to occur in Bangladesh with return periods of 5, 10, 20, and 50 years, respectively (Khan, 1993).
Hail and tornadoes affect all the areas throughout the country every year during the months of March, April, and May, being more severe in April. The occurrence of hail and tornadoes in Bangladesh is associated with the occurrence of locally severe seasonal storms, popularly known as norwesters. The tornado and hailstorms form within the norwesters and move eastward along the direction of the squall of the mother storm. These storms and tornadoes are more frequent in the afternoon. During this study, farmers in Dinajpur, Pabna, and Bogra mentioned that the occurrence of hail storms is one of the main causes of crop losses in northwestern Bangladesh.
Earthquakes and tsunamis are also significant natural hazards in Bangladesh. Although the direct impact of an earthquake on agricultural production is relative, it may affect it indirectly by affecting the irrigation and flood risk-mitigation infrastructure. The country is divided into three earthquake seismic zones, with the highest seismic activity in Zone I, covering the northern Districts from Kurigram to Moulvibazar. Experts have been forewarning a 6 to 7 magnitude earthquake to occur at any time, which would cause unimaginable destruction to infrastructure and loss of life, as well as damage to agriculture.
Map 3.4. Bangladesh: Vulnerability to Different Natural Hazards
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