Climatological Analysis of Rainfall over Hinatuan City, Surigao del Sur in eastern Mindanao—the wettest location in the Philippines

Abstract

Analysis of the daily rainfall records from 43 synoptic stations of the Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA) from 1979 to 2019 reveal that the wettest station in the Philippines is in Hinatuan City, Surigao del Sur, in eastern Mindanao Island in terms of mean annual total rainfall. Despite being located at a low elevation (~ 3 meters above sea level), the mean annual total rainfall in this station is about 4554 mm, which is roughly 700 mm more than the mean annual total rainfall in Baguio City station, the station with the highest elevation (~ 1500 meters above sea level) in the country. Further analysis of the statistical characteristics of rainfall and comparison with other stations in terms of intensity, frequency, duration (i.e., short, medium, long, and very long events), and extremes show that this station has the highest number of wet months (200–500 mm month− 1) and heavy rainfall months (> 500 mm month− 1). It also ranks first in terms of monthly rainfall amounts from January to April. This station has varying ranks across the different duration categories and is not superior compared to the other stations. The contributions of multiscale disturbances such as Tropical Cyclones (TCs), Low Pressure Systems (LPSs), and the Madden-Julian Oscillation (MJO) to the rainfall extremes over Hinatuan City station are also quantified. The results show that TCs, LPSs, and MJO contribute by about 4–17%, 2–48%, 3–40% to the monthly extremes over Hinatuan City station. The impact of LPS is more apparent between June to November. Still, the largest portion of extremes are associated with other disturbances, which contribute about 30–70%. The results of this study may serve as a basis for future characterization of the spatial variation of rainfall including the variations in extremes and their potential causes over the Philippines.