Snow Melt Rate Calculator
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border: 1px solid #e1e4e8;
border-radius: 8px;
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.smrc-calculator-box {
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Snow Melt Rate Calculator (Degree-Day Method)
Measurement System
Metric (Celsius, mm)
Imperial (Fahrenheit, inches)
Avg Daily Air Temp (°C)
Base Temperature (°C)
Terrain / Surface Condition
Custom Coefficient
Forested Area (Slow Melt)
Open / Windy Area (Fast Melt)
Glacier Ice
Rain-on-Snow Conditions
Melt Factor (mm/°C/day)
Snow Density (%)
Fresh snow ~10%, Settled ~30%, Ripened ~50%
Calculate Melt Rate
Degree Days:
–
Daily Water Equivalent (Melt):
–
Daily Snow Depth Loss:
–
How to Calculate Snow Melt Rate
Calculating the rate at which snow melts is crucial for hydrology, flood forecasting, and water resource management. The most common and practical method for estimating snow melt is the Degree-Day Method (also known as the Temperature Index Method). This approach assumes a linear relationship between air temperature and snow melt.
The Degree-Day Formula
The basic equation used in this calculator is:
M = Cm × (Ta – Tb )
M: Snow melt expressed as water equivalent (depth of water produced).Cm (Melt Factor): A coefficient representing the efficiency of melting per degree of temperature.Ta : Average daily air temperature.Tb : Base temperature (typically 0°C or 32°F), below which no melting is assumed to occur.
Understanding Melt Factors
The Melt Factor (or Degree-Day Factor) varies significantly based on environmental conditions. It aggregates the effects of solar radiation, wind speed, albedo (reflectivity), and humidity into a single coefficient.
Condition
Metric Factor (mm/°C/day)
Imperial Factor (in/°F/day)
Dense Forest
1.5 – 3.0
0.03 – 0.06
Open / Windy
3.5 – 6.0
0.07 – 0.12
Ripening Snow (Late Spring)
4.0 – 8.0
0.08 – 0.16
Glacier Ice
6.0 – 9.0
0.12 – 0.18
Water Equivalent vs. Depth Loss
It is important to distinguish between the Water Equivalent (the amount of water produced) and the Snow Depth Loss (how much the snowpack height decreases). This relationship is determined by the snow density.
Snow Density Formula:
Depth Loss = Water Equivalent / (Density %)
For example, if you generate 10mm of water from snow that has a density of 20%, the physical height of the snowpack will decrease by 50mm (10mm / 0.20).
Example Calculation
Assume an average daily temperature of 10°C in an open field (Melt Factor of 4.5 mm/°C/day ) with a snow density of 30% .
Calculate Degree Days: 10°C – 0°C (Base) = 10 Degree Days.Calculate Water Output: 10 × 4.5 = 45 mm of water produced.Calculate Depth Loss: 45 mm / 0.30 = 150 mm (15 cm) of snow depth lost.
var currentUnit = 'metric';
function updateUnits() {
var system = document.getElementById('unitSystem').value;
var lblAir = document.getElementById('lblAirTemp');
var lblBase = document.getElementById('lblBaseTemp');
var lblFactor = document.getElementById('lblMeltFactor');
var baseInput = document.getElementById('baseTemp');
var airInput = document.getElementById('airTemp');
var factorInput = document.getElementById('meltFactor');
if (system === 'metric') {
lblAir.textContent = 'Avg Daily Air Temp (°C)';
lblBase.textContent = 'Base Temperature (°C)';
lblFactor.textContent = 'Melt Factor (mm/°C/day)';
// Convert current values if they exist
if(currentUnit === 'imperial') {
if(baseInput.value) baseInput.value = ((parseFloat(baseInput.value) – 32) * 5/9).toFixed(1);
if(airInput.value) airInput.value = ((parseFloat(airInput.value) – 32) * 5/9).toFixed(1);
if(factorInput.value) factorInput.value = (parseFloat(factorInput.value) * 45.72).toFixed(2);
} else {
baseInput.value = "0";
}
currentUnit = 'metric';
} else {
lblAir.textContent = 'Avg Daily Air Temp (°F)';
lblBase.textContent = 'Base Temperature (°F)';
lblFactor.textContent = 'Melt Factor (in/°F/day)';
// Convert current values if they exist
if(currentUnit === 'metric') {
if(baseInput.value) baseInput.value = ((parseFloat(baseInput.value) * 9/5) + 32).toFixed(1);
if(airInput.value) airInput.value = ((parseFloat(airInput.value) * 9/5) + 32).toFixed(1);
if(factorInput.value) factorInput.value = (parseFloat(factorInput.value) / 45.72).toFixed(3);
} else {
baseInput.value = "32";
}
currentUnit = 'imperial';
}
updateCoefficient(); // Refresh coefficient for new unit
}
function updateCoefficient() {
var terrain = document.getElementById('terrainSelect').value;
var factorInput = document.getElementById('meltFactor');
var system = document.getElementById('unitSystem').value;
// Base metric values (mm/C/day)
var metricValues = {
'custom': null,
'forest': 2.5,
'open': 4.5,
'glacier': 7.0,
'snow_rain': 5.5
};
// Base imperial values (in/F/day) approx conversion factor ~0.0219
var imperialValues = {
'custom': null,
'forest': 0.05,
'open': 0.09,
'glacier': 0.15,
'snow_rain': 0.11
};
var val = null;
if (system === 'metric') {
val = metricValues[terrain];
} else {
val = imperialValues[terrain];
}
if (val !== null) {
factorInput.value = val;
}
}
function calculateSnowMelt() {
// 1. Get Inputs
var temp = parseFloat(document.getElementById('airTemp').value);
var base = parseFloat(document.getElementById('baseTemp').value);
var factor = parseFloat(document.getElementById('meltFactor').value);
var density = parseFloat(document.getElementById('snowDensity').value);
var system = document.getElementById('unitSystem').value;
// 2. Validate
if (isNaN(temp) || isNaN(base) || isNaN(factor) || isNaN(density)) {
alert("Please enter valid numbers for all fields.");
return;
}
if (density 100) {
alert("Snow density must be between 0 and 100%.");
return;
}
// 3. Logic
var resultDiv = document.getElementById('result');
var resDD = document.getElementById('resDegreeDays');
var resWE = document.getElementById('resWaterEq');
var resDL = document.getElementById('resDepthLoss');
var degreeDays = temp – base;
if (degreeDays 0) {
depthLoss = waterEquivalent / (density / 100);
}
// 4. Output formatting
resultDiv.style.display = 'block';
if (system === 'metric') {
resDD.textContent = degreeDays.toFixed(1) + " °C-days";
resWE.textContent = waterEquivalent.toFixed(1) + " mm";
resDL.textContent = depthLoss.toFixed(1) + " mm (" + (depthLoss/10).toFixed(1) + " cm)";
} else {
resDD.textContent = degreeDays.toFixed(1) + " °F-days";
resWE.textContent = waterEquivalent.toFixed(2) + " inches";
resDL.textContent = depthLoss.toFixed(1) + " inches";
}
}