Amid the looming threat of El Niño, the Philippine Atmospheric, Geophysical, and Astronomical Services Administration (PAGASA) is hoping that rains in the coming months will help replenish the Angat Dam reservoir, which is Metro Manila’s primary source of water supply. “From June to August, mas mataas ang probability of having above-normal rainfall condition than having below near-normal rainfall condition (the probability of having above-normal rainfall conditions is higher than having below near-normal rainfall conditions),” PAGASA-Climate Monitoring and Prediction Section Chief Ana Liza Solis said in a climate outlook forum on Wednesday, May 24. “Ito yung mataas ang posibilidad na marami ang ulan na matatanggap ng ating Angat Watershed (There is a high probability that Angat Watershed will be able to receive a significant amount of rain),” she added. Angat Dam in Bulacan (Freddie Velez/Manila Bulletin file photo)
As of 6 a.m., Wednesday, the water level at Angat Dam was at 191.35 meters, or 18.65 meters below its 210-meter normal high water level. Solis said the “best time” to conserve water at Angat Dam is from June to August. “Pagdating ng September, October, November, mas mataas na yung possibility of near-normal rainfall ang matanggap natin at mas mataas na yung probability of having below-normal rainfall over Angat watershed (When September, October, November arrives, the possibility of near-normal rainfall is now higher, as well as the probability of having below-normal rainfall over Angat watershed),” she pointed out. El Niño, which is expected to develop in the coming months, increases the possibility of “below-normal” rainfall and could have unfavorable effects, like dry spells and droughts in some regions of the country. However, Solis pointed out that during the pre-development stage of El Niño, parts of the country may still receive “above-normal” rainfall during the southwest monsoon season, or “habagat.” Based on PAGASA’s data, hydrologist Richard Orendain said Angat Dam’s level is on a “downward trend” for the last three years. “Pero kung pagbabasehan natin sa normal na pagtaas o recovery period, usually by July, start na ng recovery period ng Angat Dam (But if we base it on the normal increase or recovery period, usually by July, the recovery period of Angat Dam begins),” Orendain said. He pointed out that when the forecast basin rainfall of 320.6 millimeters is combined with Angat Dam’s current allocation of 78 cubic meters per second, the reservoir water level by June 30 is 184.38 meters. “Ineexpect natin na bababa pa ang Angat Dam. Ang good news po ay mas mataas pa rin siya sa rule curve, which is may difference siya na 2.48 meters (We expect the level of Angat Dam to further go down. The good news is that it is still higher than the rule curve, which has a difference of 2.48 meters),” Orendain said. PAGASA defines rule curve elevation as the minimum reservoir elevation needed to be maintained by dam operators to ensure the availability of water for irrigation, power generation, and domestic supply. The forecast rainfall for July is 508.8 millimeters, and based on the current dam allocation of 78 cubic meters per second, Orendain said the reservoir water level will be 187.04 meters by the end of the month. “Umpisa na ng recorvery period ng Angat Dam kung ang basin rainfall natin ay 508.8 millimeters. It is now higher than the rule curve of 180 meters for July (Angat Dam’s recovery period may already begin if our basin rainfall is 508.8 millimeters. It will also be higher than the rule curve of 180 meters for July),” he added.