🌧️ PAGASA IDF Curve Lookup

Turn your station's PAGASA RIDF (Rainfall Intensity–Duration–Frequency) equation into intensities for any storm duration, a plotted IDF curve, and a rational-method peak runoff. Learn how IDF, return period, and the rational method fit together. Free to use.

⚠️ This app ships NO rainfall data. PAGASA RIDF values are station-specific — request the RIDF table for your station from PAGASA (or use the one your professor provides), then enter its equation coefficients below. The curve and runoff this tool computes are only as correct as the coefficients you supply. Always verify against the official PAGASA RIDF.

1 · Enter your PAGASA RIDF equation

A PAGASA RIDF table gives one intensity equation per return period. Pick the form your table uses and type its coefficients. i = intensity (mm/hr), t = storm duration (minutes).

Equation form

b (min)

n (exponent)

Return period label (for your records — e.g. "25-yr")

The default coefficients above are placeholders to show the format — replace them with your station's real RIDF values.

2 · Design point & rational-method runoff (optional)

Design duration t (min) — usually t_c

Runoff coefficient C (0–1, blank to skip)

Catchment area A (hectares, blank to skip)

📊 Results

Design intensity i

—

Peak runoff Q_p

—

IDF curve

Intensity by duration

Duration t (min)	Intensity i (mm/hr)	Depth (mm)

Depth = i × (t/60), the rainfall accumulated over the duration.

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Tip: tap a category header to collapse it. This is a study aid — for design, always use the official PAGASA RIDF for your station and your professor's notes.