Influence of Multiyear Variability on the Observed Regime Shifts in Philippine Climatology

Abstract

In the advent of the new climate normal period (i.e., 1991–2020), questions are raised on what are the recent changes in the observed Philippine climatology. Here we present evidence that the Philippine climate has become warmer (i.e., increased annual surface temperatures) and wetter (i.e., increased annual rainfall) since the mid-1990s while an abrupt increase in tropical cyclone (TC) activity in the Philippines is detected in the mid-2000s. Such regime changes are mainly attributed with the shift of the Atlantic Multidecadal Oscillation (AMO) to its positive phase since the mid-1990s. A positive AMO enhances the Pacific Walker Circulation where the more intense convection center typically shifts towards the western Pacific – this translates to more rainfall, narrowing diurnal temperature range, warmer sea surface temperatures, and more intense TC activity in the Philippines. However, the recent positive AMO phase is reported as externally and possibly driven by anthropogenic warming rather than it is naturally oscillatory, which likely implies that the detected abrupt regime shifts in the Philippine climate, particularly in increased surface temperatures, are also externally driven. Our findings provide new insights on the long-term trends and variability of the Philippine climate in support of its disaster risk reduction preparedness and seasonal forecasting.