Tropical cyclones (TCs) maintain their intensity, or maximum wind speed, during landfall and the first six hours over Luzon despite crossing the Sierra Madre Mountain Range (SMMR) and Cordillera Mountain Range (CMR), according to a 2023 study.
The study by Bernard Alan Racoma and Gerry Bagtasa from the University of the Philippines Institute of Environmental Science and Meteorology published in the Philippine Journal of Science said:
(D)espite traversing Luzon and interacting with both the SMMR and CMR, the intensity of TCs does not significantly weaken on landfall and during the first 6 h traversing land regardless of the mountains’ presence.
Former Ifugao Representative Teodoro Baguilat Jr. said in a Facebook post on Oct. 24 during the onslaught of Typhoon Kristine that the Sierra Madre weakens storms entering Luzon:
Salamat palagi, Sierra Madre. Sa tuwing humihina ang bagyo sa Luzon, ikaw palagi ang dahilan (Thank you, Sierra Madre. You are always the reason every time a typhoon weakens in Luzon).
Dubbed as the “backbone of Luzon,” SMMR is the longest mountain range in the country spanning 10 provinces in Cagayan Valley, Central Luzon, and Calabarzon.
Racoma and Bagtasa used the Weather Research and Forecasting, a scientific numerical weather prediction model, to simulate the influence of the SMMR and CMR on 45 Luzon-passing tropical cyclones from 2000 to 2020. They ran simulations with both the original topography and flattened terrain of the mountain ranges.
The t-test results yielded a probability value (p-value) of 0.80 for the difference between the unmodified terrain and flattened terrain runs for SMMR and 0.73 for CMR, higher than the 0.05 cutoff. The higher p-values indicate that the differences are not statistically significant or that the mountain ranges have no mitigating effect on the TCs.
The study found that the SMMR reduces wind field strength by -30% only over the eastern parts of the Bicol region and Catanduanes islands.
Results also showed the mountain ranges slow tropical cyclones’ translational speed, the distance traveled over time, increasing the period communities are exposed to wind and rain hazards.
The barrier effect of the SMMR depends on the location and the hazard involved, the study said.
For example, the mountain range reduces wind hazard exposure in Cagayan Valley and western and central Luzon by up to 13%. It also increases rainfall along its western slopes (25-55% in Metro Manila) but decreases rainfall in Cagayan Valley by 10-59%.
Using the same method, a 2016 study by Racoma and Bagtasa with other climate scientists said the slowing effect of SMMR on typhoon Labuyo, tropical storms Undoy and Mario led to increased rainfall along the mountain range.
As of writing, Baguilat’s post has garnered 31,000 reactions, 271 comments and 30,000 shares. (IA)