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 reveals that the wettest station in the Philippines is in Hinatuan City, Surigao del Sur, in eastern Mindanao Island in terms of the mean annual total rainfall. Despite being located at a low elevation (∼ 3 m above sea level), the mean annual total rainfall in this station is about 4554 mm, which is approximately 700 mm more than the mean annual total rainfall in Baguio City station, the station with the highest elevation (∼ 1500 m 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 (1 − 2 days), medium (3 − 7 days), long (8 − 14 days), and very long (> 14 days) events), and 95th percentile extremes show that this station ranks first in terms of the frequency of wet months (200–500 mm month^− 1) and heavy rainfall months (> 500 mm month^− 1), mean monthly rainfall amounts from January to April, and the mean rainfall amount in the short duration category. The contributions of multiscale factors 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 about 0–5%, 0–38%, 3–38% to the monthly extremes over Hinatuan City station, respectively. Cases when TCs or LPSs are located within 1100 km radius centered at Hinatuan City station while MJO is active were also found and their contributions to the monthly extremes are 0–4% and 0–12%, respectively. The largest portion of the extremes are associated with other unaccounted factors, which contribute about 49–71%. 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