This calculator helps estimate the daily evaporation rate of a pond based on environmental factors. Understanding evaporation is crucial for pond management, especially in arid regions or for water conservation efforts.
The unobstructed distance over which wind blows across the water surface.
function calculateEvaporation() {
var pondArea = parseFloat(document.getElementById("pondArea").value);
var fetchDistance = parseFloat(document.getElementById("fetchDistance").value);
var airTemperature = parseFloat(document.getElementById("airTemperature").value);
var waterTemperature = parseFloat(document.getElementById("waterTemperature").value);
var relativeHumidity = parseFloat(document.getElementById("relativeHumidity").value);
var windSpeed = parseFloat(document.getElementById("windSpeed").value);
var resultElement = document.getElementById("result");
resultElement.innerHTML = ""; // Clear previous result
// Basic validation
if (isNaN(pondArea) || pondArea <= 0 ||
isNaN(fetchDistance) || fetchDistance <= 0 ||
isNaN(airTemperature) ||
isNaN(waterTemperature) ||
isNaN(relativeHumidity) || relativeHumidity 100 ||
isNaN(windSpeed) || windSpeed < 0) {
resultElement.innerHTML = "Please enter valid positive numbers for all fields. Humidity must be between 0 and 100.";
return;
}
// — Evaporation Calculation (Simplified – Meyer Formula Adaptation) —
// This is a simplified model. More complex models exist (e.g., Penman-Monteith).
// The Meyer formula is often adapted for open water bodies.
// 1. Saturation Vapor Pressure (ea) in kPa at water surface temperature
var ea = 0.6108 * Math.exp((17.27 * waterTemperature) / (waterTemperature + 237.3));
// 2. Actual Vapor Pressure (e) in kPa from air temperature and humidity
var e = ea * (relativeHumidity / 100.0);
// 3. Vapor Pressure Deficit (VPD) in kPa
var vpd = ea – e;
if (vpd < 0) vpd = 0; // Vapor pressure deficit cannot be negative
// 4. Wind Factor (Kw) – This is a highly simplified representation.
// Real-world K values depend on fetch and other factors.
// A common approach is to use a coefficient that increases with wind speed and fetch.
// For simplicity, let's use a basic wind speed multiplier that's somewhat influenced by fetch.
var windFactor = (0.4 + 0.2 * windSpeed) * (1 + 0.05 * fetchDistance);
if (windFactor < 0.4) windFactor = 0.4; // Minimum factor
// 5. Daily Evaporation (E) in mm/day
// Formula: E = Kw * (ea – e)
var dailyEvaporation_mm = windFactor * vpd;
// 6. Total Daily Evaporation in Liters (1 mm over 1 m² = 1 Liter)
var dailyEvaporation_Liters = dailyEvaporation_mm * pondArea;
// 7. Convert to m³ for larger ponds if desired
var dailyEvaporation_m3 = dailyEvaporation_Liters / 1000.0;
resultElement.innerHTML = "Estimated Daily Evaporation Rate:" +
dailyEvaporation_mm.toFixed(2) + " mm/day" +
dailyEvaporation_Liters.toFixed(2) + " Liters/day" +
dailyEvaporation_m3.toFixed(3) + " m³/day";
}