2.4 Conclusions

The local rain gauge recordings in Quezon City already indicate the magnitude of the Habagat of August 2012 event. However, the rain gauge data alone could not provide a complete picture of what happened around Metropolitan Manila from 6 to 9 August.

Only the combination of the Subic S-band radar and the dense rain gauge network around Metropolitan Manila reveals that a significant portion of the heavy rainfall was dropped right over the shorelines of Manila Bay. Assuming a scenario in which the rainfall field was shifted eastwards by no more than 20 km, the peak discharge of the Marikina River would have increased by almost 30%, potentially resulting into a return period well beyond the 150 yr of Typhoon Ketsana in September 2009. It appears that—despite the terrible harm and damage that was caused by this flood event—the Habagat of August 2012 was no more than a glimpse of the disaster that Metropolitan Manila missed by no more than 20 km.

Nonetheless, a lot of open questions remain to be answered, particularly concerning the underestimation of rainfall by the radar, the potential effects of inhomogeneous vertical reflectivity profiles, the potential role of wind drift (from Manila Bay to Metropolitan Manila), and also the hydrological processes which resulted from the rainfall event. Beyond, additional data for the region are available from a C-band weather radar located near Tagaytay City. However, these data were not considered in this study since the role of attenuation induced by heavy rainfall has yet to be determined. All these questions need to be addressed as soon as possible so that the equipment installed can allow for the most accurate analysis of extreme rain events that certainly will occur in the future. However, even with the current level of data processing, the recently installed Philippine radar network demonstrates a huge potential for high-resolution rainfall monitoring as well as for risk mitigation and management in the Philippines.