Preparing for storm surges
It is appalling to see the death and devastation which the Supertyphoon “Yolanda” brought to Tacloban, Ormoc and several other areas in the country.
Although Tacloban and Ormoc have the same magnitude of physical destruction caused by the strong winds of the typhoon, an estimated 2,500 died in Tacloban, while only around 20 casualties have been reported in Ormoc City. The storm surge that occurred at the height of the supertyphoon in Tacloban City was likely the one responsible for the deaths of thousands.
Although both a tsunami and a storm surge are characterized by an increase in the level of sea water, flooding the areas along the coast, they are actually two different natural phenomena.
A tsunami is usually caused by earthquakes, undersea landslides and volcanic eruptions. A storm surge is an abnormal rise of sea water level whipped up by a storm, over and above the predicted increase in the tides, such as when there is high tide. Extreme flooding in coastal areas is caused by the rise in water level, which is made worse when the storm surge coincides with normal high tide.
Storm surge
A storm surge is predominantly wind-carried. Just imagine the water being pushed to the shore by the strong winds of the storm. And if you have a storm whose winds were as strong as Yolanda’s, the resulting storm tide can reach up to seven meters or higher and the death and destruction it can cause is unimaginable. In coastal areas in a typhoon-prone country like the Philippines, a storm surge is often the greatest threat to life and property.
Before Yolanda, the worst storm surge was caused by Hurricane “Katrina” in the United States. At least 1,500 people perished and many of these deaths were attributed directly, or indirectly, to the storm surge.
According to an expert interviewed on CNN, a storm surge is a complex phenomenon, the magnitude of which for a particular location depends on a number of different factors, such as storm intensity, forward speed, size (radius of maximum winds), angle of approach to the coast, central pressure, and the shape and characteristics of the coast.
The width and slope of the coastal shelf impact the magnitude of the resulting storm surge. For example, a shallow slope and wide shelf, such as those of the Tacloban and Boracay coasts, can produce a greater storm surge of about 20 feet or higher than a shore with a steep shelf, wherein the continental shelf drops off very quickly, such as the Palawan shoreline. Here, the same storm would cause a storm surge of around eight- or nine-foot waves.
The battering waves, carrying with them immense power of approximately 1,700 pounds per cubic yard, can damage even concrete buildings, and can sweep away and drown people and animals easily. Big storm surges not only affect the coast but could also extend inland like what happened in Tacloban City. In low-lying areas, a storm surge can extend up to several kilometers inland.
What happened in Tacloban was an unfortunate confluence of events. A local expert said that the storm surge came on top of a high tide; hence, it reached areas which would otherwise have been safe. The powerful winds of Yolanda magnified the destructive powers of the pounding waves which literally destroyed every structure and many living beings along their way. The typhoon ripped off roofs, knocked down concrete structures, washed away roads and vehicles including big trucks on them, and even ran aground one ship.
Near-perfect accuracy
The Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pag-asa) has to be commended for the near-perfect accuracy in predicting the strength and path of Yolanda. It’s especially challenging to forecast the path since it could be erratic. It was just unfortunate that although Pagasa, and even CNN, has been warning all residents of coastal areas including Tacloban of the danger of storm surges, many did not know what a storm surge was. And they were completely caught off guard.
It’s counterproductive to point fingers at anyone at this point, but it’s worthwhile to stress the importance of a more proactive local disaster preparedness so that this tragedy would not be repeated again. Yolanda will not be the last of our supertyphoons, so all coastal and risk-prone areas should have a good disaster preparedness plan, with back-up contingency plans. Urgent execution of plans for worst-case scenarios every time there’s a major typhoon affecting the area should be done.
It’s better to overreact even if nothing happens, than to underreact and massive tragedy the magnitude of what happened in Tacloban City strikes.
