Photos by IDS-Comval
With rainy season around, typhoons and floods are not far behind. As more typhoons – 15 or less – are expected before the year ends, floods will become a common thing Davao Region and other low-lying areas in the Philippines.
A flood is an overflow of water that submerges land which is normally dry. “Floods are due to the complex combination of weather, climatic and human activities,” explained Rosalie C. Pagulayan, weather specialist II of the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) during a seminar workshop convened by the Department of Science and Technology in Davao City some years back. “Most floods occur as a result of moderate-to-large-scale rainfall events.”
The Philippines, given the location and the topography of the country, experiences five weather-causing phenomena which can bring floods. These are: thunderstorms, cold front, monsoons, intertropical convergence zone (ITCZ), and tropical cyclones.
Thunderstorms, called local storms, occur when towering cumulus clouds reach a height where the temperature is well below the freezing point. Among the associated hazards are heavy rain (which may cause flashflood) and lightning (which may cause death, burns or fire).
Cold front is formed when cold air moves over areas of warm air. Since cold air is heavier than warm air, the warm air is pushed aloft by the cold air giving rise to widespread cloudiness. The cold front affects the eastern part of the country from November to late April or early May.
There are two types of monsoon: Southwest and Northeast. In the former, the Asiatic continent becomes warmer than the surrounding seas and a low pressure cell develops over the continent. This causes a flow of moist southwest wind over the Philippine area. At times, when this southwest flow becomes thick in depth, it persists for a long period causing continuous rains which may last for weeks during the months of June to September. The Southwest monsoon is responsible for the great portion of rainfall during the country’s wet season.
One of the worst Southwest monsoons that hit the country happened last year when an eight-day period of thunderstorm and torrential rain deluged the National Capital Region, the provinces of the Quezon, Cavite, Laguna, Rizal, Bulacan, Pampanga and Bataan.
In Northeast monsoon, the Asiatic continent is snowbound and the high pressure cell over China sends northeasterly winds over the Philippines giving the country cold temperatures, and causing much rainfall over the eastern coasts. This happens from November to February.
Known by sailors as the doldrums, the ITCZ is an area where the northern hemisphere trades meet the southern hemisphere trades. According to the weather bureau, ITCZ is characterized by towering clouds of cumulonimbus clouds accompanied with showers of widespread thunderstorms.
“The axis of convergence, which is usually oriented in an east to west direction, does not remain stationery at the equator but migrates north or south of the equator,” PAGASA’s briefing paper explains. In the Philippines, it oscillates during the months of May to October.
Tropical cyclones are low pressure systems characterized by relatively low atmospheric pressure at the center with very strong winds blowing counterclockwise (in the northern hemisphere) towards and around the center. The 1972 flood in Central Luzon was due to four storms that hit the region from July to August. The 1991 flash flood that happened in Ormoc City was due to Typhoon Uring.
All these weather disturbances bring a lot of water causing flooding in affected areas. The same thing happens when there is a storm surge, “a rise of seawater above the normal level on the coast generated by the action of the wind and atmospheric pressure, associated with the occurrence of a tropical cyclone.”
According to PAGASA briefing paper, a storm surge can inundate low-lying coastal communities as the level of the ocean is raised by several feet. This happened in Metro Manila in 2011, when large waves that hammered the coastline of Manila Bay caused flash floods in areas. The huge waves caused by the storm surge battered the bay’s seawall, causing portions of the wall to collapse.
Likewise, high tide that coincides with high stream flows can aggravate flooding near the coasts. Early this year, torrential rains inundated many barangays in Davao City as Bankerohan River overflowed and submerged houses along river banks displacing hundreds of residents.
As floods are common throughout the country, the weather bureau has launched the Flood Early Warning System (FEWS) capacities. It has five basic elements: prediction, detection, communication, decision-making, and mobilization.
“In any disaster of given magnitude, the first line of defense is still awareness of the communities at risk,” reminded Pagulayan.
Another PAGASA briefing paper shared some safety tips before flooding, during the flood, and after the flood. It said that when warned of flood, the following should be done. Securely anchor weak houses. Drinking waters must be stored in containers as water service may be interrupted. Household belongings should be moved to upper levels while livestock are bought to higher grounds.
Should there is an advice of an evacuation, it must be followed. “Do not panic, move to a safe area before access is cut-off by floodwaters,” it said. “Turn off main electricity switch and gas valve, and lock your house before evacuating.”
Before flooding occurs, keep these in mind: Keep informed of the daily weather conditions and forecast from the weather bureau. Be aware how often your location is likely to be flooded and to what extent. Know the flood warning system and evacuation plan of your community and make sure your family knows them. Designate an evacuation area for the family and livestock and assign family members specific instructions and responsibilities according to an evacuation plan. Keep a stock of food which requires no or little cooking and refrigeration, good at least for 3 days. Keep a transistorized radio and flashlight with spare batteries, emergency cooking equipment, candles, matches, and first aid kid hand in case of emergency.
During the flood, stay indoors. Do not attempt to cross rivers with flowing streams where water is above the knee. Beware of water-covered roads and bridges. Do not go swimming or boating in swollen rivers. Beware of contaminated food and water.
After the flood, here are the things you need to do: Reenter the house with caution using flashlights. Flammables and dangerous animals like snakes may be inside. Be alert for fire hazards like broken electric wires. Do not eat food and drink water until they have been checked for flood water contamination.
Report broken utility lines (electricity, water, gas, and telephone) to appropriate agencies or authorities. Do not turn on the main switch or use appliances and other equipment until they have been checked by competent electrician. Do not go “sight-seeing” in disaster area. Your presence might hamper rescue and other emergency operations.
It’s rainy season again – and forearmed is forewarned. Listen to the woes of one flood victim: “The downpour of rain is unprecedented. The rain came without much warning. When we woke up in the morning, there was intermittent heavy rain and I thought that it is seasonal – indeed the rainfall throughout this year has been quite heavy, unlike during the last three years. The rain water reached two feet on the main streets. I couldn’t drive, there was water everywhere.”
