Enhanced Habagat
The southwest monsoon, locally known as Habagat, is a normal occurrence in the Philippines. Between the months of June to October, warm and moist winds travel towards the western coasts of the Philippines. Warmer air means the air can hold more water according to the Clausius-Clapeyron equation (Skliris, 2016). This increase in water capacity can then bring in more rain. As such, during the the peak Habagat season in the months of July, August, and September, high rainfall is expected.
Back in August 2012 when the Nationwide Operational Assessment of Hazards (NOAH) was a relatively young organization, we underwent what we call our “trial by fire”. Typhoon Saola (local name Gener) was about to leave the Philippines when Typhoon Haikui immediately came rushing afterwards. While both Tropical Cyclones did not make landfall in the country, the swirling dance of these storms was strong enough to pull in extreme rains from the southwest monsoon.
NOAH offered two things: near-real time weather information and hazard maps. The near-real time weather information could tell you when extreme rainfall could be coming, and where it will be falling. The hazard maps, on the other hand gave people an idea what kind of hazards we are expecting based on the incoming rain. These were critical during the August 2012 storms, and people were visiting our website by the thousands so they could access the said information. There were only four of us operating the website during the storm, and needless to say, we weren’t able to sleep properly that week.
To help us remember the horrors of this storm, we eventually decided to call it Habagat 2012.
Habagat 2012 brought 1,007.5mm of rain in 3 days, causing ₱3 billion in damages, leaving 109 people dead (Rappler 2013).
Just when we thought that this was a one time thing, it happened again in 2013.
In the third week of August that year, Tropical Storm Trami (local name Maring) pulled in the southwest monsoon, causing what we now call Habagat 2013. The combined systems of a cyclone and monsoon brought 1,120.2 mm of rain in 5 days, causing ₱ 689 million in damages, and leaving 27 dead (Rappler 2013).
As it started to become a yearly thing, the media and the weather bureau coined a new term: Enhanced Habagat.
During monsoon season, whenever Tropical Cyclones are expected to graze the Philippine Area of Responsibility without making landfall, people start to ask, “will it enhance Habagat?”
Will it happen again?
The thing is while people have been starting to ask if incoming Tropical Cyclones will enhance the monsoon, we then forget to ask, “has this happened before?”
My thesis mainly deals with Tropical Cyclones and extreme precipitation. While working on my thesis yesterday, I was looking through historical Tropical Cyclone archives along with historical precipitation archives.
It turns out that these enhanced Habagat rains have already happened before. The figure below shows enhanced Habagat maps for 1978, 1979, and 2007. Based on the records, there have been some cases of Tropical Cyclones in August that barely grazed the Philippine Area of Responsibility while causing more than 400mm of rainfall in 3 days.
Similar to other enhanced Habagat events, these Tropical Cyclones did not make landfall in the Philippines.
(as always, I did not explore data prior to 1978, but I have a feeling that there are more enhanced Habagat events way way back).
If it has been happening before, why are we only noticing it now? In one interview I gave a few years back, I mentioned that the number of Tropical Cyclones has not been increasing (David, et al 2013). It’s just that information is easier to share these days (lindol? tweet! baha? tweet! bagyo? selfie!). And thus while it seems like these disasters are happening more often, we just see them more often online. They could have been happening before but we just don’t remember them. Or it’s possible we weren’t even born yet when such incidents happen. In the same interview, a friend even remarked that if memory serves him correct, things could have been worse 3,000 years ago.
But there are a few things we are certain of. First, the climate is changing, the atmosphere is warming. How that will affect Tropical Cyclones in the Philippines is still subject to research, but we are not optimistic.
Second, while the Philippines is on its way to becoming one of the fastest growing economies, it’s also becoming one of the fastest growing populations. And as they say, there is no such thing as natural disasters since hazards only become disasters if people or resources are involved. And with more resources, assets, and people in the country, we are at risk for more disasters.
Will there be an enhanced Habagat event this year? We don’t know yet. It’s only May, and peak monsoon season is not until August. We can’t predict Tropical Cyclones that far in the future. But armed with the knowledge that it has happened before and it can happen again, we can at least prepare for incoming typhoons or rains, no matter how strong they could become.
Data (free!)
- International Best Track Archive for Climate Stewardship (IBTrACS) https://www.ncdc.noaa.gov/ibtracs/index.php?name=ib-v4-access
- Asian Precipitation — Highly-Resolved Observational Data Integration Towards Evaluation of Extreme Events (APHRODITE-2) http://aphrodite.st.hirosaki-u.ac.jp/
References
- BY THE NUMBERS: Ondoy, Habagat 2012, Habagat 2013. (n.d.). Retrieved May 9, 2019, from Rappler website: http://www.rappler.com//newsbreak/39948-by-the-numbers-ondoy-habagat-2012-2013
- David, C.C., Racoma, B.B., Gonzales, J., and Clutario, M. (2013). A Manifestation of Climate Change? A Look at Typhoon Yolanda in Relation to the Historical Tropical Cyclone Archive. Science Diliman, Vol 25 (2): 79–86.
- Skliris, N., Zika, J. D., Nurser, G., Josey, S. A., & Marsh, R. (2016). Global water cycle amplifying at less than the Clausius-Clapeyron rate. Scientific Reports, 6(1), 38752. https://doi.org/10.1038/srep38752
- Ybanez, R., Alconis, J., Crisologo, I., Eco, R., Racoma, B., Lagmay, A. (2013), First Use of Early Warning System “Project NOAH” during August 2012 Metro Manila Extreme Flooding, At: Brisbane, Australia, Conference: AOGS Annual Meeting, Affiliation: Asia-Oceania Geosciences Society, DOI: 10.13140/RG.2.1.1515.0960 (available via ResearchGate)
