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IDF Curves

The IDF Curves tab assembles fitted Intensity–Duration–Frequency (and depth–duration–frequency) curves across durations, and builds design storms.

IDF curves — intensity vs duration, one line per return period IDF curves — intensity vs duration, one line per return period
IDF curves — intensity vs duration, one line per return period. Circles are observed durations, squares are ratio-estimated. (Illustrative synthetic data.)

Controls

  • Distribution — Gumbel (EV1), GEV, Log-Normal, or Pearson III — and Parameter estimation: Method of moments (the ECCC default), Maximum likelihood, or L-moments.
  • View — IDF Curves, DDF Curves, or Intensity Heatmap.
  • Options
    • Show fitted curves — draw the smoothing curve through the per-duration quantile points.
    • Curve form — Log-log linear (ECCC) or Sherman \(i = a/(d+b)^c\).
    • Climate-change uplift — apply a percentage allowance to the final intensity/depth values (the historical fit is untouched and the uplift is disclosed in the title, report, and exports).
    • Show 95% confidence intervals — bootstrap limits (with a Bootstrap samples count); markedly slower for GEV and Pearson III.
DDF curves — rainfall depth vs duration, one line per return period DDF curves — rainfall depth vs duration, one line per return period
The DDF view — the same fit shown as depth (mm) rather than intensity. (Illustrative synthetic data.)

Screening

Like the Analysis tab, this tab has its own independent Completeness screening and Exclude outliers sections, and a Compare impact… button that renders the curves with and without screening. Outlier removal here applies to observed durations.

Outputs

Run from ▶ Run IDF (cancellable mid-run). The result toolbar offers:

  • Pop out — open the plot in a resizable window for report sizing.
  • Export tables… — Excel (intensity, depth, CI bands, and a metadata sheet) or CSV.
  • Design storm… — generate a Chicago or alternating-block hyetograph (and SCS / NRCS distributions) from the fitted curves.

Notes

  • The run log reports which durations are observed versus estimated. For daily-only records, sub-daily depths are estimated from ecozone depth ratios and are approximate — see Why sub-daily estimates are approximate and the ratio methodology.
  • The ecozone used comes from the active location set on the Map tab.
  • The curve-fit forms (log-log linear, Sherman) and the design-storm methods (Chicago, alternating-block, SCS / NRCS) are summarised, with their sources, in the Methods overview.

See also: Analysis · Methods & References