Yes, it's raining, but not much over Angat Dam

MANILA, Philippines – It's been nearly two weeks since the start of the rainy season, but the water level of the Angat Dam in Bulacan continues to drop. Why?

The Philippine Atmospheric, Geophysical, and Astronomical Services Administration (PAGASA) explained on Wednesday, June 26, that the rain simply isn't falling that much over the Angat Dam yet.

This is bad news for residents in parts of Metro Manila, Rizal, and Cavite, who are still dealing with daily water interruptions due to the Angat Dam's critically low level. (READ: Manila Water and Maynilad schedules)

"Kung napapansin 'nyo, 'yung Bulacan-Norzagaray area, hindi po gano'n kalakas 'yung ulan doon, sa may bandang eastern section. Ang malakas po dito, dito sa bandang western section [like Quezon City].... 'Yung Angat may ulan, pero light lang...kaya hindi tumaas 'yung tubig," said PAGASA Weather Division Chief Esperanza Cayanan in a press briefing on Wednesday morning.

(If you notice, in the Bulacan-Norzagaray area, the rain there isn't that heavy, in the eastern section. The rain is heavy here, here in the western section [like Quezon City].... There's rain over the Angat Dam, but it's just light...which is why the dam's water level isn't going up.)

The Angat Dam's water level was at 158.40 meters as of 6 am on Wednesday, 0.37 meters lower than its level at 6 am on Tuesday, June 25.

The minimum operating water level (MOWL) of the Angat Dam is 180 meters. It had gone below 180 meters last April, during the dry season, then plunged below the critical low level of 160 meters last Saturday, June 22.

When will the Angat Dam's water level normalize? It may take 2 to 3 more months before the dam recovers, or by August or September.

While the MOWL is 180 meters, the normal high water level (NHWL) of the Angat Dam is 210 meters.

"Hindi natin siya nakikita na biglang tataas except kung merong bagyo na talagang tatama, dadaan, at magbubuhos ng ulan doon mismo sa Angat Dam," Cayanan said.

(We don't expect its water level to quickly rise except if there are tropical cyclones which will really hit, pass through, or bring rain right over the Angat Dam.)

PAGASA data show that 50% of the Philippines' annual rainfall comes from tropical cyclones. In 2019, there have been 4 tropical cyclones, so far, and the total estimate for the entire year is 14 to 18. (READ: FAST FACTS: Tropical cyclones, rainfall advisories)

How about the La Mesa Dam? The La Mesa Dam in Quezon City is gradually seeing improvement due to the southwest monsoon or hanging habagat and thunderstorms.

According to PAGASA, the effects of the southwest monsoon are usually felt before dawn until early morning, and then mid-afternoon until evening. Thunderstorms are usually in the afternoon or evening.

"'Yun 'yung maganda dito sa La Mesa Dam, kasi tuwing hapon nagkaro'n ng mga thunderstorms and then sa madaling araw naman nagkaro'n ng habagat. So palaging merong pandagdag na tubig sa dam natin, sa La Mesa Dam, unlike Angat," said PAGASA Assistant Weather Services Chief Rene Paciente in the press briefing.

(That's what's good about the La Mesa Dam, because during the afternoon there are thunderstorms and then in the wee hours there's the southwest monsoon. So there's always a source of rain to fill up the dam, the La Mesa Dam, unlike Angat.)

The La Mesa Dam's water level was at 69.98 meters as of 6 am on Wednesday, 0.78 meters higher than its level at 6 am on Tuesday. Its NHWL is 80.15 meters.

The Angat Dam supplies around 96% of Metro Manila's water needs. From Angat, water flows through the Ipo Dam, then to the La Mesa Dam, before reaching consumers. – Rappler.com