Flood Susceptibility

Flood susceptibility is the single biggest reason Filipino homes lose value, and it is the first thing this report checks. UP NOAH (the government's flood-hazard project) has mapped the whole country into three flood levels: Low, Medium, and High. We take your exact coordinates and ask one question first: does this point fall inside a flood polygon, and if so, at what level?

On top of the level, NOAH tags each zone with a return period. A "5-year" flood is the kind of water you can expect roughly every rainy season. A "100-year" flood is the once-in-a-generation, Ondoy-grade event. The same High label means something very different at 5 years versus 100, so we surface both.

The Philippines sits in the most active typhoon basin on Earth. Around twenty storms enter the area each year, and eight or nine make landfall. Flooding, not wind, is what reaches most homes.

Tropical Storm Ondoy (2009) and Typhoon Ulysses (2020) both put parts of Metro Manila under roof-high water. Buyers who only saw a property on a sunny day had no way to know the lot sat in a Level 3 zone until the water arrived. This layer is that missing context, delivered before you sign.

First a point-in-polygon test (PostGIS ST_Contains) checks whether your coordinate sits inside a flood polygon, returning the worst level found there.

If you are outside every zone, we measure the distance to the nearest flood edge. A 50 m proximity buffer catches lots sitting right on the lip of a zone, and a 200 m buffer flags properties next to a Level 3 area, because flood water does not respect a polygon's exact boundary.

Flood polygons come from the UP NOAH Center / DOST nationwide flood-hazard dataset, the same maps that LGUs and disaster offices use for planning.

We simplify the polygon edges slightly for speed (about 11 m on the ground) and subdivide them so a dense Manila address still answers in milliseconds, but the coverage is preserved exactly.