Researchers may well try to see if these flooding events are somewhat related to climate events such as El Nino or La Nina. Also they may take note of how long the floods lasted before it subsided.
One very documented flood is the one that deluged Manila in November 1943. This is so significant that all writers of WWII memoirs recall it since it marked the start of the worst aspects of the Japanese occupation. The flood deluged parts of Manila under 2 meters of water as told by memoir writers Joaquin L Garcia and Benito Legarda Jr. Legarda even mentions how his father's Faura barometer plunged and then rose again as the storm passed. Based on Legarda's recollection, the heavy rain period started after lunch and ended 8 hours later. This 7 hour deluge is similar to what we experienced last September 26. Garcia lived across St Scho near DLSU and if that area sank in 2 m of water, then that is indeed like what Ondoy dished us. However unlike Ondoy, the water subsided immediately. During that time, the mountains surrounding Manila were not yet completely denuded and the waterways were still unobstructed.
But it is the more recent floods that we should take another look at. The Ormoc deluge of November 7, 1991 was brought about by a weak tropical depression (TD Uring (Thelma). As intense rainfall fell on a 100% denuded watershed, the water rose to more than 3 meters in Ormoc City within 4 hours. Seven thousand deaths were recorded and in one district of the city, only 200 out of 2500 residents survived. Ormoc City and its watershed has an area of 616.6 sq km. Uring dumped 580 mm of rain near Ormoc.
Since then we have had these type of floods in Bicol, Mindanao and more recently in July 2008 in Iloilo as a result of Typhoon Frank. Metro Manila residents while they read the news, were mostly unconcerned. The capital has more flood infrastructure and that being the center for national life and the economy, should be able to handle the usual floods.
But September 26 flushed away all of that. Metro Manila while having almost the same area as Ormoc 617 sq km, is almost completely built up. It thus became a mega Ormoc disaster. We haven't finally assessed the toll in lives and property lost or damaged but it is likely much much more than what was lost in Ormoc City.
Two weeks later crazy Typhoon Pepang (Parma) deluged the provinces of Tarlac, Pampanga, Nueva Ecija, Pangasinan and Cagayan. Pangasinan is the worst hit. All of Luzon's dams filled beyond capacity and had to release water. Again water rose to more than 3 meters in less than an hour. Luzon's > 5% forest cover is also attributed as a factor in the disaster.
Metro Manila and progressive northern Luzon has been hit with Ormoc style deluges. Perhaps Metro Manila has bought itself what Jared Diamond wrote in his book "Collapse" "the privilege of being the last to drown"
Ormoc City should have warned us of the dire consequences. Did we heed the message? We are quite sure that an event like this will happen again and again, as history tells us. What can we do?
After we have assessed the damage and began the reconstruction we have to reconstruct with one thing in mind...
Plant more trees!