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Tropical Cyclone Sidr devastates Bangladesh

By: Dr. Jeff Masters, 3:22 PM GMT on November 16, 2007

Tropical Cyclone Sidr has devastated the low-lying nation of Bangladesh. At least 496 are dead, 540 missing, and thousands injured. The cyclone's 150 mph winds and storm surge of at least 20 feet destroyed tens of thousands of buildings, and have left over 100,00 people homeless. A nation-wide power outage hit the country in the wake of Sidr, making communications difficult. Power is only now beginning to be restored to some regions. Most of the reported deaths were from collapsed buildings and flying debris hurled by the Category 4 cyclone, which hit the country at 9pm local time Thursday night. The storm moved northeastward across the country, and has now dissipated in the foothills of the Himalaya Mountains.

Figure 1. Population density map of Bangladesh for regions less than 10 meters in elevation (red areas) and higher than 10 meters (green areas). The path of Tropical Cyclone Sidr took it inland over the Sundarbans Forest, the least populated region of the coast. However, the more heavily populated provinces just to the right of the Forest, Barguna and Patuakhali, likely received a storm surge of 10-20 feet. Sidr passed near the city of Barisal, where sustained winds of 92 mph were measured at midnight local time. The deadliest cyclones for Bangladesh have always taken a more easterly track, near the city of Chittagong. Image credit: CIESEN, Columbia University. Thanks go to Margie Kieper for finding the image.

Sidr's storm surge
Storm surge is usually the biggest killer in Bangladesh cyclones, and was responsible for the vast majority of the 140,000 people killed in the 1991 Bangladesh Cyclone. This storm struck eastern Bangladesh as a Category 5 cyclone--the only Category 5 cyclone on record to hit the country. The triangular shape of Bengal Bay funnels high surges into the apex of the triangle where Bangladesh sits, and the shallow bottom of the bay allows extraordinarily high storm surges to pile up. The maximum storm surge from Sidr was probably 20-25 feet, and affected the regions near and to the right of where the eye made landfall. The eye fortunately came ashore in the Sundarbans Forest, the world's largest forest of mangrove trees. This region is the least populated coastal area in the country (Figure 1). Storm surge levels of 10-20 feet probably affected the provinces of Barguna and Paruakhali, which are more heavily populated. Undoubtedly, the storm surge killed many more people in these provinces, and Sidr's death toll will go much higher. However, Bangladesh has done a much better job providing shelters and evacuating people during cyclones since the 1991 storm. Over 650,000 people did evacuate from Sidr, and it is unlikely the death toll will put the storm on the list of the world's deadliest cyclones of all time. Bangladesh already holds ten of the top twenty spots on that list.

Jeff Masters

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