WunderBlog Archive » Category 6™

Category 6 has moved! See the latest from Dr. Jeff Masters and Bob Henson here.

Top weather story of 2008: Cyclone Nargis

By: Dr. Jeff Masters, 5:04 PM GMT on January 05, 2009

The top weather story of 2008 has to be the catastrophic impact of Cyclone Nargis on the nation of Myanmar (formerly Burma). Nargis (the Urdu word for 'daffodil') hit the low-lying, densely populated Irrawaddy Delta region of Myanmar on May 2, 2008. Nargis' Category 4 winds of 135 mph brought a storm surge of up to 4 meters (13 feet) to the coast, inundating regions up to 40 km inland. At least 140,000 people perished, according to official estimates by the U.N. and the government of Myanmar. This makes Nargis the ninth deadliest cyclone in world history. The storm made 800,000 people homeless, destroying 450,000 homes. Approximately 2.4 million people were significantly affected by the cyclone, and total damage has been estimated at $4 billion.

Recovery from the cyclone will take years. The loss of livestock, buffalo for plowing, fishing nets, and boats was near total in many regions of the coast. Fallen trees still block many transportation routes, and the much of the rich farmland used to grow crops has been made salty by the inland penetration of Nargis' storm surge. About 30% of the villages in the devastated region still have a high proportion of their homes using plastic or canvas sheeting for roofs or walls, and undernutrition and lack of clean water are still problematic. However, international aid has made a big difference, and much of the affected area has benefited from the aid.

A once-in-500-year event for Myanmar?
Tropical cyclones are uncommon in Myanmar, which has had only six Category 1 or stronger storms since 1970, and eleven since 1948. Nargis is the third strongest cyclone on record to hit Myanmar, and the deadliest and most damaging. The previous highest death toll from a tropical cyclone in Myanmar was 187, during the Category 1 storm that hit on May 7, 1975. Nargis is the first major tropical cyclone to hit Myanmar since Category 3 Cyclone Mala hit on April 28, 2006. Mala hit a less populated area less prone to storm surge, and killed 22 people and damaged 6000 buildings. It is remarkable that no other tropical cyclone over the past 300 years has hit the Irrawaddy Delta and caused major loss of life. An unusually strong and far-southward extending trough of low pressure turned Nargis to the east much farther south than is the norm for the North Indian Ocean. In the pre-1970 years, there is only one hurricane-force storm recorded to have hit Burma, a Category 1 cyclone in 1936 that killed 36 people. A significant cyclone hitting the Irrawaddy Delta causing thousands of deaths would very likely have been recorded, had this happened any time in the past 300 years. Such events were recorded in both India and Bangladesh during that period. Nargis appears to have been the only major tropical cyclone to hit the Irrawaddy River Delta in recorded history, and may be a once-in-500-year event.

Figure 1. Visible satellite image of Nargis shortly before landfall. Image credit:NASA.

Nargis' storm surge
Nargis took the worst possible path, tracking right along the low-lying, heavily populated Irrawaddy River Delta. Moreover, the storm hit at high tide, greatly increasing the impact of the storm surge. Tidal range in the Irrawaddy River Delta is about five feet between low tide and high tide, and the death toll would have been much, much lower had the storm hit at low tide. Further amplifying the storm surge's height was the fact that Nargis was moving rather slowly--about 11 mph. Slow moving tropical cyclones can drive a much higher storm surge into narrow estuaries that connect to the ocean, since there is more time for the surge to penetrate inland. Nargis' track, forward speed, and high tide timing created a "perfect storm" able to cause an unprecedented storm surge in the Irrawaddy River Delta. The only saving grace was the relatively small size of the cyclone.

Human factors helped make the storm surge worse. About 80% of the mangrove forest along Myanmar's coast has been destroyed, to make room for rice paddies and shrimp farms. Mangroves--tall, gnarly, salt-tolerant trees--act to blunt and slow down the progress of the storm surge and reduce the wave action of the ocean. Had more mangroves been left to survive, the impact of the storm surge would have been lessened. How much so, no one can say, for there are few observations of the storm surge to verify models of this. Keep in mind that the mangroves are far more effective in protecting against a sudden, powerful wave like the 2004 tsunami, compared to the slower, hours-long inundation of a storm surge.

Figure 2. Topography of Myanmar, with track of Cyclone Nargis superimposed. Image credit: NASA.

Failure of the Myanmar government
Nargis was remarkable not only for its death toll, but for the failure of Myanmar's dictatorship to provide adequate warnings before the storm. The Indian Meteorological Department (IMD), which is responsible for tropical cyclones warnings in the North Indian Ocean, classified Nargis as a "severe cyclonic storm" three days prior to landfall, and warned of landfall in Myanmar of Nargis as a Category 1 or 2 storm. However, the official state-controlled New Light of Myanmar newspaper carried this forecast the day before landfall: "the severe tropical cyclone NARGIS...is forecast to cross the coast during the next 36 hours...Under the influence of this storm, rain or thundershowers will be widespread...frequent squalls with rough seas will be experienced off and along the Myanmar coast. Surface wind speed in squalls may reach [50] mph." This forecast was buried on page 15 of the miscellaneous section of the newspaper. No mention of hurricane-force winds or of Nargis' storm surge was made. However, the IMD does not make forecasts of storm surge, which is something that needs to be corrected in the future, according to an excellent assessment of Cyclone Nargis published in Nature by Dr. Peter Webster of Georgia Tech. Dr. Webster also advocates that a relatively small investment by the developed world in improved warning systems and shelters for the region can dramatically lower death tolls and the money needed for aid responses for future storms. Sounds like a great investment to me!

Finally, Nargis was also remarkable for the initial refusal of Myanmar's government to allow foreign aid into the country after the storm. Over a week passed before significant aid was allowed in, which greatly exacerbated the suffering of the storm victims and undoubtedly led to a higher death toll.

Nargis links
Post-Nargis Joint Assessment (July 2008).
Post-Nargis Periodic Review I (December 2008).
Nature paper by Dr. Peter Webster of Georgia Tech (July 2008).

My next blog post will be Wednesday or Thursday, when I'll continue to report on the major weather and climate events of 2008.

Jeff Masters

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.