Friday, November 8, 2013

Haiyan's Surge May Have Been Highest in East Asia History

Tropical Cyclone Haiyan slammed into the Philippines today, likely generating the most intense wind speeds at landfall of any tropical cyclone in recorded history, according to the Weather Underground. Jeff Master's blog stated, "Haiyan had winds of 190 - 195 mph at landfall, making it the strongest tropical cyclone on record to make landfall in world history." It appears as though Haiyan's intensity may have eclipsed the former record held by Hurricane Camille, which struck the Mississippi Coast of the United States in 1969.

 Tropical Cyclone Haiyan generated incredible winds exceeding 190MPH at landfall as it slammed into the island of Samar in the Philippines. Image Source: McIDAS.

It's very possible that Haiyan generated the highest storm surge in the history of East Asia, however, it will take time to measure the high water marks. The highest storm surges in East Asia have occurred in the Philippines, as the archipelago experiences frequent strikes from intense tropical cyclones.

Although we are looking into reports of a 10 meter (32.8 foot) surge that may have impacted the Philippines in 1968, at the moment the highest confirmed surge event in East Asia was a 7.3-meter (24 foot) storm tide that struck the Philippines in 1897 (Arafiles et al. 1978) . This cyclone, called the Typhoon of Samar and Leyte, struck on October 12, 1897, generated a peak water level at Hernani and Tanglad. Hernani is located just north of Haiyan's landfall, and would have experienced very intense onshore winds during Haiyan. The storm tide from the 1897 cyclone killed 1,300 people.

Tropical Cyclone Haiyan impacted the same area as the Typhoon of Samar and Leyte (1897), which generated the highest verifiable storm surge in the history of East Asia and drowned 1300 people. Image:  AFP PHOTO/CHARISM SAYAT/AFP/Getty Images

An interesting aspect of many Philippine storm surges is that coastal shape and configuration tends to play an important role for generating very localized surge events. This is because the Philippines is an archipelago of islands, many of which have large inlets and bays. Water tends to funnel into these areas, causing very high storm surge levels, while locations just a few miles away may observe relatively low water rises.

Take the 1897 surge event, for example. Storm surge levels varied greatly over relatively short distances, mostly because of coastal configuration. Arafiles and Alcances (1986) state, “The observed surge was 7.3 meters (24 ft.) above mean sea level at Hernani and Tanglad, Samar and the water level remained at this height for about two hours. This unusual height of the observed surge was to some extent magnified by the coastal configuration. In comparison, Pambuyan, which is better protected and had a rise of only 1.5 meters (4.9 ft.) while Guiuan, only 0.7 meters (2.3 ft.). Again to illustrate the effects of coastal topography, Basey had an observed surge of 4.9 meters (16 ft.) while Tacloban only 0.4 meters (1.3 ft.). It will be noted that there were many instances when coastal configuration played a vital role in further magnifying the total storm tide.”

Such history comes to life now, as Tropical Cyclone Haiyan has struck this same area. Haiyan made landfall on Samar, near Guiuan, and areas such as Hernani, which observed the highest storm tide levels in 1897, where located north of Haiyan’s track, and likely also observed very high water levels today. The 1897 cyclone shows us that this area has the potential to observe a surge of at least 7 meters (23 feet), and given Haiyan’s incredible intensity, we must wonder if some locations observed surge levels on par with the 1897 storm. The most positive aspect about Haiyan is that the forward speed of this story was relatively fast. Slower moving cyclones tend to build up higher storm surges.

Massive waves crash into the shoreline near Legazpi City, Philippines (Image: AP Photo/Nelson Salting)

A regional comparison shows that the highest surges in the Philippines have been larger than in other countries of East Asia. China’s highest storm surge was 5.94 meters (19.5 feet) at Nandu Tide Gage in 1980, while Japan’s highest storm surge occurred in the Isewan Typhoon (Vera) of 1959, when the water level reached 3.5 m (11.5 feet).

SURGEDAT has identified 113 storm surge events in East Asia, through the 2012 season. More than 25 of these events occurred in the Philippines, however, we’re still completing this dataset. Look for an updated global dataset to be uploaded to our website next spring, while we submit a paper on global storm surge observations and impacts.

The Southern Impact Planning Program (SCIPP) has funded the development of SURGEDAT, as SCIPP conducts stakeholder-driven research related to weather and climate hazards that impact six states in the South Central U.S. SCIPP has conducted much research and outreach related to storm surge, as this hazard has severely impacted the U.S. Gulf Coast. The global SURGEDAT database enables SCIPP to conduct data-driven research, such as investigating how tropical cyclone (hurricane) characteristics impact storm surge heights. Including international events in the database provides more comprehensive data and analysis, which ultimately will improve storm surge models.

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