Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather
By: Dr. Jeff Masters , 2:33 PM GMT on 五月 05, 2008
A disaster of horrific proportions has befallen Myanmar, where the death toll is now over 4,000, with thousands more missing, in the wake of Cyclone Nargis. Nargis--a popular woman's name in India--is the deadliest and most destructive tropical cyclone ever to hit Myanmar (Burma). The storm hit the coast of Myanmar Friday night as borderline Category 3/Category 4 cyclone, with winds of 130-135 mph. After passing over the low-lying and densely populated Irrawaddy River delta region, Nargis made a direct hit on the capital city of Rangoon (Yangon), as a Category 1 storm with top winds of 80 mph. Winds at the Yangon airport hit 69 mph, gusting to 138 mph, at 5:30am local time on Saturday. The anemometer failed at that point, and the winds likely rose higher.
Figure 1. Population density of Myanmar, with Nargis' track superimposed. Nargis passed over some of the most densely populated regions of the country. Image credit: Columbia University's CIESEN.
However, it was the storm surge, not the winds, that was the big killer in Nargis. The storm tracked over the low-lying Irrawaddy River delta region, which is highly vulnerable to storm surge deaths due to its low elevation, dense population, and limited hurricane awareness of the people. I could find no records of a major tropical cyclone ever making a direct hit on the Irrawaddy River delta. The ocean bottom off the coast of Myanmar is quite shallow (Figure 2). A large area of Continental Shelf waters with depth 200 meters or less extends far out to sea. This is a situation similar to the Gulf of Mexico, and is ideal for allowing large surge surge to pile up over the shallow waters. The counter-clockwise circulation of winds around Nargis likely built up a storm surge of at least 4 meters (13 feet), that then smashed ashore into the Irrawaddy Delta region, drowning thousands of people.
Figure 2. Bathymetry of the Bay of Bengal. The shallow waters of the Continental Shelf (mostly shallower than 200 meters) are shaded whitish-grey. The shallow waters south of Rangoon allowed the counter-clockwise circulation or winds around Nargis to pile up a large storm surge to the right of the storm's track. Image credit:geomapapp.org.
Storm surges of four meters have been recorded along the Myanmar coast in at least one other cyclone. The Gwa cyclone of May 4, 1982--a Category 4 storm with 140 mph winds--hit just north of where Nargis struck, and carried a four meter high storm surge to the coast. Fortunately, that storm hit far enough north that it was not able to pile up a huge storm surge along the southern shore of the Irrawaddy Delta. The official death toll from the Gwa cyclone was only five people, but was probably very much higher. The military junta that has controlled Myanmar since 1962 has been known to conceal the number of people killed in natural disasters. The highest official death toll from a tropical cyclone in Myanmar is 187, during the Category 1 storm that hit on May 7, 1975. According to a email I received form Chris Burt, author of the excellent book Extreme Weather:
Statistics concerning disasters in Burma since the mid-1960s must be viewed with some skepticism since the authorities always want to pretend they have control of all situations whether natural or societal, and outsiders are never allowed access to devastated sites--I am sure this will be the case again with Cyclone Nargis. We may never know the true magnitude of what happened. I was in Rangoon just 7 weeks ago (I've been visiting Burma for 30 years on a regular basis--every year since) and can tell you that if winds as strong as reported occurred, the damage must be enormous (the vast majority of structures in the city are poorly built and even the newer construction was not constructed with CAT 3 winds in mind.
During the tsunami event of Dec. 26, 2005 the 'official' death toll was something like 69, but in reality many hundreds were killed (estimates 300-800) in the Mergui Archipelago just north of the Thai border. In fact, not included in the official death toll (in Burma or Thailand) were hundreds and perhaps 1,000 illegal Burmese immigrants working in the hotel industry at Kao Lak in Thailand (just north of Phuket where the worst damage occurred in Thailand).
Figure 3. Simulated storm surge of the May 4, 1982 cyclone that hit Gwa, Myanmar. The Gwa cyclone was a Category 4 storm with 140 mph winds shortly before landfall. Storm surge values of four meters (13 feet) were measured and simulated just to the right of where the the cyclone hit the coast. Note that the counter-clockwise circulation around the cyclone also drove a high storm surge into the bay just east of Rangoon. The reported death toll was only five, but was probably much higher. Image credit: "Simulation of Storm Surges Along Myanmar Coast Using a Location Specific Numerical Model" (Jain et al., Natural Hazards 39, 1, September 2006).
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