PDD Positive Degree Days Melt

Apply separate snow/ice positive-degree-day factors sequentially while exhausting a supplied snow-water reservoir; interval temperatures are means and no snow replenishment is assumed.

Description

Positive-degree-day models relate warmth to melt through empirical factors.

Positive-degree-day models relate warmth to melt through empirical factors. Snow and exposed ice can use different factors, so exhausting a snow reservoir changes subsequent melt.

Apply separate snow/ice positive-degree-day factors sequentially while exhausting a supplied snow-water reservoir; interval temperatures are means and no snow replenishment is assumed.

When to use PDD Positive Degree Days Melt

Use this for the following task: Apply separate snow/ice positive-degree-day factors sequentially while exhausting a supplied snow-water reservoir; interval temperatures are means and no snow replenishment is assumed.

Prepare the measurements and calibration parameters in the declared units. Keep vector entries aligned and choose a consistent spatial frame and time basis.

How to use PDD Positive Degree Days Melt and understand its results

Prepare the measurements and calibration parameters in the declared units. Keep vector entries aligned and choose a consistent spatial frame and time basis.
Enter meanTemperaturesC, intervalDays, initialSnowWaterEquivalentMm, snowDegreeDayFactorMmPerCDay, iceDegreeDayFactorMmPerCDay using the field table, then run the tool.
Read snowMeltMm, iceMeltMm, remainingSnowMm, totalMeltMmWaterEquivalent. Interpret flags, units, ordering and placeholder values using the rules below.
Review any reported issue or failed check, correct the supplied values when appropriate, and verify the result in its intended context.

Input field	Meaning	Value type and bounds	Requirement
meanTemperaturesC	Mean temperatures c	list of number; each entry: number	Required
intervalDays	Interval days	list of number; each entry: number	Required
initialSnowWaterEquivalentMm	Initial snow water equivalent mm	number	Required
snowDegreeDayFactorMmPerCDay	Snow degree day factor mm per c day	number	Required
iceDegreeDayFactorMmPerCDay	Ice degree day factor mm per c day	number	Required

Process aligned intervals in order. Consume snow first, convert its melt back to used degree days, apply leftover warmth to ice, and sum water-equivalent melt.^[1]

PDD = max(0,T)Δdays; snow = min(reservoir, snowFactor×PDD); ice = iceFactor×remaining PDD

This summarizes the declared operation. Units, indexing, inclusivity and exceptional cases are explained in the surrounding text.

Output field	Meaning	Value type
snowMeltMm	Snow melt mm	list of number
iceMeltMm	Ice melt mm	list of number
remainingSnowMm	Remaining snow mm	number
totalMeltMmWaterEquivalent	Total melt mm water equivalent	number

json

{
  "input": {
    "meanTemperaturesC": [
      -1,
      2,
      4
    ],
    "intervalDays": [
      1,
      1,
      1
    ],
    "initialSnowWaterEquivalentMm": 6,
    "snowDegreeDayFactorMmPerCDay": 3,
    "iceDegreeDayFactorMmPerCDay": 5
  },
  "output": {
    "snowMeltMm": [
      0,
      6,
      0
    ],
    "iceMeltMm": [
      0,
      0,
      20
    ],
    "remainingSnowMm": 0,
    "totalMeltMmWaterEquivalent": 26
  }
}

Limitations and assumptions

Mean temperatures miss within-interval positive excursions. The initial snow reservoir is not replenished and factors must be calibrated.

Constants and empirical coefficients are supplied rather than calibrated. Check units and observational applicability before interpreting the model. Malformed requests produce input errors. A successfully evaluated request can still contain false flags, empty result lists or a result outside the supplied threshold; those outcomes have the meanings stated above.

Alternative or Complementary methods

Choose Geothermal Flux Basal Melt for this operation: Convert net geothermal-minus-conductive basal heat to signed ice melt under pressure-melting conditions; negative flux represents freezing potential, not guaranteed actual freezing. For a complementary task, use Melt Pond Fraction Albedo Feedback for this operation: Quantify area-weighted pond/ice albedo and incremental absorbed shortwave for supplied pond scenarios; no melt-rate or radiative-feedback climate prediction.

The implementation reference documents the exact calculation, supported input shapes and returned fields.

References

PDD Positive Degree Days Melt — tool.io

Similar or alternative tools

Geothermal Flux Basal Melt
Convert net geothermal-minus-conductive basal heat to signed ice melt under pressure-melting conditions; negative flux represents freezing potential, not guaranteed actual freezing.
Melt Pond Fraction Albedo Feedback
Quantify area-weighted pond/ice albedo and incremental absorbed shortwave for supplied pond scenarios; no melt-rate or radiative-feedback climate prediction.