Diurnal Characterization of Localized Convective Rain Events in Urban Metro Manila, Philippines

The diurnal characteristics of localized rain events were investigated using observed rainfall data from 16 automated weather stations (AWS) in Metro Manila, Philippines during the period 2013 - 2014. Total rainfall was partitioned into four rain types: tropical cyclone (TC) rain, typhoon-enhanced rain (TER), stratiform rain, and convective rain, to determine the proportion of rain that is purely due to localized convection. The diurnal patterns of frequency and intensity of convective rain are investigated during the seasons of northeast monsoon (November to March), summer (April to May), and southwest monsoon (June to October). A set of criteria was adapted to further verify and characterize these localized rain events. The criteria considered maximum changes in meteorological variables, including wind speed, wind direction, pressure, temperature, and dew point temperature. Results show that the northern area of Metro Manila received more rainfall amount throughout the period compared to the total rainfall in the southern areas. While the highest total amount of rainfall was observed during the southwest monsoon season of the period, it is during the summer season that the largest proportion of the rainfall amount, which is approximately 380 mm, was attributed to convective rain. Almost 55% of the total afternoon rain events and 36% of the total evening rain events were identified as strong convective rain events based on the set of criteria. Localized rain events in Metro Manila were found to be more prominent and vigorous in the afternoon than in the evening during summer season, when the convection is mainly due to the heating of the land and is not affected by other synoptic systems such as tropical cyclones and monsoon activities. Furthermore, these localized rain events in Metro Manila have been observed to propagate from the northeastern side of the area towards the south and move along the direction of the prevailing wind during summer season of 2013-2014.