[H-CG22] Adaptation to climate change and its social implementation

[HCG22-02] Historical and Future Synoptic Conditions over the Philippines and their Implications for Extreme Rainfall over the Country

*Alyssa Gewell Agena Llorin ¹, KOJI DAIRAKU¹ (1.University of Tsukuba)

Keywords:principal component analysis, synoptic conditions, extreme rainfall , Philippines

Increasing trends in extreme rainfall over the Philippines threaten worsening damages and associated costs, exacerbated by the country’s vulnerability to climate change. Unfortunately, existing research on extreme rainfall formation in this region is still limited due to its complex features and sparse automated weather station records. This study aims to address this research gap by establishing the synoptic conditions most conducive to extreme rainfall events in the Philippines and exploring the frequency of these conditions in future climate scenarios. The methodology mainly involves using the principal component analysis (PCA) technique. The dominant patterns in geopotential height at 850 hPa over the Philippines from 1991 to 2021 are first identified using ECMWF Reanalysis ERA5 data. Daily rainfall data provided by the Philippine Atmospheric, Geophysical, and Astronomical Services Administration (PAGASA) agency covering the same period is used to compute rainfall indices under each identified synoptic pattern. Finally, the PCA technique is applied to the historical and SSP5-8.5 scenarios of selected CMIP6 global climate models (GCM). The Mann-Kendall trend test is applied to the calculated principal components to understand how the signal magnitudes of each synoptic pattern will change in future decades. Preliminary results show that while the most dominant synoptic patterns cover the expected equatorial low band, subtropical high band, and intertropical convergence zone (ITCZ) transition over the country, a substantial amount of days still feature distinct low-pressure systems in the country’s vicinity. The third and sixth most dominant patterns, which had a low-pressure system directly over and to the northeast of the country, respectively, were associated with most of the extreme rainfall amounts recorded. Both the MPI-ESM1-2HR and EC-Earth3 GCMs show decreasing annual contributions from the third and fourth patterns during the 2015-2100 period. The results of this study confirm the potential of the PCA technique for synoptic climatology over the Philippines and should aid in forming the framework needed to understand extreme rainfall in this region.