Dam releases change the timing and the peak of what arrives downstream, and no hazard map models them. Here is what to ask and who to ask.
A large reservoir upstream changes the river below it. Most of the time it reduces flooding, which is one of the reasons dams get built. During a large rainfall event it can do the opposite, because a reservoir that is full has to pass what comes in.
If your property is on a river below a major dam, that is part of your hazard picture, and it is not on any screening.
Mapped flood susceptibility describes where water goes given modelled rainfall and the shape of the land. Dam operation is a human decision made in real time, based on reservoir level, inflow forecasts, and downstream conditions.
That is an operational question, not a terrain question. No point-level national dataset encodes it, and printing a rating for it would be inventing a number. The general principle is in a layer came back blank on your report.
Quite a lot, actually. The terrain does not care where the water came from.
A property that screens clean on all three is in a better position regardless of dam operations. A property that screens as high susceptibility close to the channel is exposed to both rain and releases.
The operating agency. Major Philippine dams are operated by the National Irrigation Administration, the National Power Corporation, or their concessionaires, depending on the dam. Ask:
The provincial and municipal DRRM office. Ask how the warning reaches households, especially at night, and where the evacuation points are.
The barangay. Ask what happened in the last big release, how much notice people got, and how high the water reached.
The neighbours. Ask the same, and ask how many times.
The most common failure is not the absence of a warning, it is that the warning does not reach the household. Ask specifically:
Test it. If you cannot find out how you would be told, you would not be told.
The flooding in the Cagayan Valley during Typhoon Ulysses in November 2020 produced a long public argument about how much came from rainfall and how much from releases at Magat Dam. Both were involved.
For a buyer the argument matters less than the lesson: a reservoir upstream is part of the system, its behaviour under stress is not something you control, and the households that fared best were the ones who knew the warning existed and where to go. See Ulysses, November 2020.
A hazard screening describes terrain and mapped susceptibility at a point. It does not model reservoir operations, forecast inflow, or issue warnings. The operating agency and your local DRRM office are the authorities on releases, and PAGASA on the rainfall driving them.
CheckHazard does not replace a professional geotechnical or engineering survey.