Understanding the 2008 Cyclone in Myanmar

Formation of a Cyclone

Figure 1: Cyclone Formation, source: Jarreau, Paige Brown. "Storms Inside Storms" SciLogs International. Web.

Hurricanes, or cyclones in the southeastern Indian and southwestern Pacific and Oceans, are major atmospheric disturbances that occur between five and 30 degrees latitude on either side of the equator. They frequently begin as weak easterly winds in water at a temperature greater than 80 degrees Fahrenheit and at a depth of greater than 50 meters. 

Under such conditions, air begins to flow counterclockwise into the center of the storm as high pressure areas converge on the low pressure easterly wind. This converging air rises and diverges again in a clockwise motion higher up in the troposphere (see figure 1). The bands of thunderstorms are formed by conditionally unstable air as warm air is continuously rising compared to more dense cold air around it. Such a process is known as convergence and is most common near the equator in tropical climates near the Inter Tropical Convergence Zone (ITCZ). This creates a steep pressure gradient which forces air into the center of the storm. While there is rising air in the thunderstorm band around the eye, there is a sinking air within the eye, where weather conditions are relatively calm. On average, the eye of a cyclone is 30 miles in diameter and the diameter of an entire cyclone is approximately 120 miles wide on average. 

The biggest threat to human life during a hurricane is not high wind speeds but rather the storm surge. Storm surges are accompanied with hurricanes and cyclones making landfall. A large displacement of water is caused by conditional atmospheric instability and heavy winds. A tall surge over a low-lying coastal area can cause inundation for miles while wiping out critical infrastructure and homes. Poor land use can amplify the effects of a storm surge. For instance, mangroves and forests have proven to be effective natural barriers during heavy storm surges and tsunamis. 

The Saffir-Simpson Scale

In order to be classified a cyclone, a tropical storm much reach wind speeds of at least 74 miles per hour (mph). When it does, it becomes a Category 1 on the Saffir-Simpson Scale. At 157 mph, it becomes a Category 5 which is the highest ranking and can cause extensive damage to life sustaining infrastructure.

Figure 2: "Saffir-Simpson Hurricane Scale," Scioly.org. Web.

When a cyclone approaches land it begins to diminish in wind speed. However, cyclone winds can also create a storm surge to low-lying and unprotected areas. Such a situation poses a flooding risk to many coastal cities. Despite a weakening as a cyclone gets closer to land, waves may pose the most significant threat.

Formation of Cyclone Nargis in the Indian Ocean

Cyclone Nargis 

Figure 3: The Path of Cyclone Nargis. Source: NASA: Hurricane Season 2008, web. 

On April 28th, 2008, scientists began tracking Cyclone Nargis off of the coast of Myanmar. During its path towards India, scientists projected that the storm would turn on the normal cyclone track up towards Bangladesh or into the mountainous area of western Myanmar. However, the cyclone took an unpredictable path towards the Irrawaddy Delta. Citizens in this low-lying area did not anticipate such a storm.

Nargis made landfall on May 2, 2008 as a Category 3 storm with winds up to 120 mph. However, the more significant component of the event was the storm surge: 12 feet high and extending up to 24 miles inland. Due to the unusual track of the storm, the people living in the densely populated Irrawaddy Delta region outside of and in Yangon were largely unprepared for Nargis which would remain a cyclone until May 4, 2008.

Figure 3:"Myanmar Population Density, 2015," Encyclopedia Britannica, web. 

As shown by figure 3, the Irrawaddy Delta region, which is south and southwest of Yangon, is one of the most densely populated areas of Myanmar. Therefore, while wind force played a factor in the destruction of homes, the storm surge was most responsible for the predicted 200,000 deaths and the destruction of 95% of buildings in the delta. The Irriwaddy is a saltwater area that is almost entirely at sea level.

Poor Land Use Patterns and Warm Waters

In addition to a lack of warning time for those living in the Irrawaddy Delta, the region is also a critical area for both rice paddy and shrimp farming. However, farming practices prior to the 2008 cyclone had eliminated large swaths of mangrove forests that can act as a natural barrier to storm surges. This likely intensified the level of destruction and death wrought by Nargis. Some scientists also believe that climate change and warmer waters may have played a role in the destructive path of this storm. Although the track of a cyclone or hurricane is nearly impossible to predict, unseasonably warm surface temperatures allowed Nargis to remain strong as it moved on an usual trajectory. 

Limited Evacuation Plans for Yangon

Figure 4: Yangon after Nargis. Source: "Yangon, Myanmar" Doctors without Borders, web.

Under a strict military government during 2008, Myanmar had little access to news and warning systems as an underdeveloped country. Additionally many did not have access to cars. Infrastructure in and around Yangon is informal and does not meet any regulated building codes. With a storm that shifted tracks in a matter of hours, the city and its surrounding areas did not stand a chance.

Figure 4 illustrates the level of devastation in and around the city where 95% of all homes were eviscerated by Nargis and especially its storm surge and flooding. In a country with limited access to technology to drain the waters and to clear people from the area, the water stagnated for long periods of time as deaths continued to grow in the aftermath of the event. Additionally, the flooding brought an additional problem that mangroves could have helped to prevent as a natural barrier. The shrimp and rice farms were flooded and largely destroyed by the cyclone.

Explaining the Damage Caused by Cyclone Nagis

Sources


"Case Study: Cyclone Nargis." BBC News. Accessed 9 April 2016. Updated 2014. Web. 

"Hurricane Season 2008: Tropical Storm Nargis (Indian Ocean)." NASA. Accessed 9 April 2016. Updated 20 May 2008. Web. 

"Myanmar Population Density, 2015," Encyclopedia Britannica. Accessed 9 April 2016. Updated 2015. Web. 

Paige Brown, Jarreau. "Storms Inside Storms." SciLogs International. Accessed 9 April 2016. Updated 4 September 2011. Web. 

"Saffir-Simpson Hurricane Scale." Scioly.org. Accessed 9 April 2016. Web.

"Why the Cyclone in Myanmar was so Deadly." National Geographic. Accessed 9 April 2016. Published 8 May 2008. Web. 

"Yangon, Myanmar." Doctors without Borders. Accessed 9 April 2016. Updated 7 May 2008. Web.