Simple Daily Intensity Index SDII

Compute SDII using observed precipitation only on wet days at caller inclusive threshold; zero observed wet days is undefined rather than inventing a daily intensity.

Description

The simple daily intensity index describes average precipitation on wet days.

The simple daily intensity index describes average precipitation on wet days. Its denominator counts wet days rather than all days, so it separates rainfall intensity from how often rain occurs.^{[1, 2]}

Compute SDII using observed precipitation only on wet days at caller inclusive threshold; zero observed wet days is undefined rather than inventing a daily intensity.

When to use Simple Daily Intensity Index SDII

Use this tool to compute SDII using observed precipitation only on wet days at caller inclusive threshold; zero observed wet days is undefined rather than inventing a daily intensity.

Prepare the climate observations and any independently chosen thresholds or model parameters. Confirm units, daily coverage, time order and the intended seasonal window.

How to use Simple Daily Intensity Index SDII and understand its results

Prepare the climate observations and any independently chosen thresholds or model parameters. Confirm units, daily coverage, time order and the intended seasonal window.
Enter dailyPrecipitationMm, callerWetDayThresholdMm using the field table and calculation rules, then run the tool.
Read wetDayCount, totalWetDayPrecipitationMm, simpleDailyIntensityMmPerWetDay. The explanation below defines the units, signs, ordering and any flags or placeholder values.
If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.

Input field	Meaning	Value type; see rules below	Requirement
dailyPrecipitationMm	Daily precipitation mm	list of number	Required
callerWetDayThresholdMm	Caller wet day threshold mm	number	Required

Enter nonnegative daily precipitation in mm and a positive wet-day threshold. A value equal to the threshold counts as wet. The tool sums precipitation on qualifying days, counts those days and divides the sum by that count to return mm per wet day. It rejects input with no wet days.

SDII = Σ P_i over P_i ≥ wet threshold / number of qualifying wet days

Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.

Output field	Meaning	Value type
wetDayCount	Wet day count	number
totalWetDayPrecipitationMm	Total wet day precipitation mm	number
simpleDailyIntensityMmPerWetDay	Simple daily intensity mm per wet day	number

json

{
  "input": {
    "dailyPrecipitationMm": [
      0,
      1,
      3
    ],
    "callerWetDayThresholdMm": 1
  },
  "output": {
    "wetDayCount": 2,
    "totalWetDayPrecipitationMm": 4,
    "simpleDailyIntensityMmPerWetDay": 2
  }
}

Limitations and assumptions

Choose a threshold appropriate to the index convention and gauge resolution. The tool does not fill observation gaps or assess rainfall intensity within a day. A high wet-day mean can result from a few extreme days or many moderately wet days.

Numeric inputs and returned numeric values must be finite; an unrepresentable returned value produces an error. Numeric lists are limited to 100,000 entries; the rules above may require smaller limits. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use Wet Spell Length Analyzer: Analyze full consecutive wet spell distribution at a caller inclusive precipitation threshold; supplied sequence must have no missing days and zero means no observed qualifying spell. For a complementary task, use Rainy Days Threshold Counter: Audit a supplied increasing rain-threshold policy over observed daily precipitation with coverage denominator; no missing-as-dry treatment or climate category lookup.

Further background: Climate extreme index definitions.

References

Simple Daily Intensity Index SDII — tool.io
Climate extreme index definitions — Climdex

Similar or alternative tools

Wet Spell Length Analyzer
Analyze full consecutive wet spell distribution at a caller inclusive precipitation threshold; supplied sequence must have no missing days and zero means no observed qualifying spell.
Rainy Days Threshold Counter
Audit a supplied increasing rain-threshold policy over observed daily precipitation with coverage denominator; no missing-as-dry treatment or climate category lookup.