Does the Sierra Madre Mountain Range in Luzon Act as a Barrier to Typhoons?

Abstract

Tropical cyclones (TCs) making landfall in Luzon weaken due to the surface friction of Luzon’s mountainous terrain and the reduced ocean heat, momentum, and moisture fluxes over the landmass. Landmass also influences TC rain distribution by orographic enhancement or blocking of a TC’s moisture-laden circulation. In this study, we investigated the influence of the effects of the Sierra Madre and the Cordillera Mountains Ranges (SMMR and CMR) on TC-associated wind and rainfall hazards to answer the question of whether the SMMR or the CMR mitigates TC hazards. We used the Weather Research and Forecasting (WRF) model with modified SMMR and CMR terrains to disentangle the effects of the orography with flat land. Results show that Luzon-passing TCs maintain their intensities at landfall regardless of the frictional effects of the mountain ranges but the CMR inhibits the re-intensification of westward-moving TCs emerging from landmass after traversing Luzon. The SMMR reduces wind exposure and basin-wide rainfall of the Cagayan Valley. Hence, the SMMR can be considered a barrier for that region. In addition, the weakening effect of the SMMR reduces the wind exposure of the island of Catanduanes and eastern Bicol the most. However, for the rest of Luzon, the SMMR enhances rainfall which will likely compensate for the slight decrease in wind exposure – especially considering that most TC-related damages are water/rainfall related. The CMR, overall, has a larger hazard-mitigating effect than the SMMR. In any case, we believe that shifting the discourse to these mountains’ biodiversity conservation and restoration – rather than their purported TC mitigating effects – will be more strategically constructive.