January 2023 floods in the Philippines and Climate Change
Interview by the Washington Post
Is this sort of flooding normal in the Philippines — and is it normal in the months of December/January? Is climate change predicted to make this worse?
There are two ways to look at this:
First is to look at the trend analysis on rainfall in the Philippines. There is an undergraduate research study by Kenneth Brian Anareta (with Prof. Richmark Macuha [rnmacuha@up.edu.ph] as thesis adviser) from the UP Institute of Civil Engineering, where he has conducted trend analysis of rainfall data across weather stations in the Pasig - Marikina- Laguna De Bay basins (where Metro Manila is situated). The trend analysis of the rainfall data suggests that:
There will be an overall increase in rainfall intensity from 2022 to 2050 during the dry season (which includes January), with a maximum increase of 40% projected.
The subsequent spatial analysis suggests that Metro Manila will have wetter days during the dry season, and the typically wet portions of the basin will be drier during the wet season.
The third impact assessment on climate change (https://www.sciencedirect.com/science/article/pii/S2225603220300199) also suggests that there will be an average 16.5 percent increase in rainfall by 2055.
Second is to look at the catalysts of the rainfall. The recent rainfall was caused by a low-pressure area, which typically develops into tropical cyclones. Comparing the trends of tropical cyclone (TC) probabilities (a byproduct of my analysis on typhoons) of the period from 1977 to 2010 and the period from 2011-2021 suggests an overall increase in TC probability for January.
Figure 1. Change in TC Probability - 1977-2010 vs. 2011-2021. (Areas in red suggest that there has been an increase in TC Probability within the past 12 years)
The data for the percent increase are as follows:
Southern Luzon (including Metro Manila)
Mean: 115%
Median: 147%
Palawan
Mean: 180%
Median: 147%
Visayas
Mean: 72.79%
Median: 106%
Mindanao
Mean: 71.06%
Median: 54.55%
Summing all the findings suggests that the increase in temperature increases the probability of tropical cyclone formation (genesis), resulting in an increase in average and maximum precipitation that tropical cyclones typically bring.
Is the Philippines equipped to handle this kind of flooding? What should the Philippines do to become more resilient?
Filipinos are well aware that the Philippines is famously known for its resilience against natural hazards. But having known for resiliency also resulted in some drawbacks. Many Filipinos are confused in drawing semantics from the natural hazards they are exposed to, as they term the resulting calamity or tragic events as a "natural disaster." The confusion is seemingly innocent, but they are stripped of the reality that it is only the hazards that are natural but not the disaster that they have been caused, as humans mainly cause the disaster for their lack of response. Filipinos are indeed aware that they are vulnerable to flood, but whether they are equipped to respond to it is another thing. Also, due to our political culture, much focus was put on disaster relief (where personalities seize opportunities to put themselves in a good light through philanthropy) rather than on disaster prevention (where comprehensive disaster risk management is needed, with science steering the policies). I think I have also answered the follow-up question in the previous sentences. For more information about resilience, it is better to ask our resident resilience engineer, Dr. Harold M. Aquino [dmaquino@up.edu.ph].
What makes these typhoons or rains so fatal in the Philippines? Why do people die?
Risk is a product of three factors: hazard, exposure, and vulnerability. Hazard pertains to the flood height and/or the speed of the floodwaters. Exposure pertains to the location of the houses, whether the houses were in the areas where flooding will most likely happen. The vulnerability pertains to the capability of the houses exposed to the risk of not sustaining damage nor subjecting their occupants to risk during a flooding event with a given flood height and/or speed. We have already mentioned the hazard, with the increasing trend of rainfall intensity and frequency of flooding events. Exposure suggests that a higher portion of the population is residing in areas where there is a high probability of flooding to occur. Vulnerability can point to the fragility of the houses being built in these highly-exposed areas, being made with flimsy materials, or having a total height less than the height of flood that has occurred or will occur. Combine those three, and we have our worst-case scenario where most of the population is situated in areas with high flood risk while residing in houses/structures that are incapable of sustaining the risk posed by the increasing flood hazards due to the increasing rainfall intensity.