#evaporation-calculator {
font-family: sans-serif;
border: 1px solid #ccc;
padding: 20px;
border-radius: 8px;
max-width: 600px;
margin: 20px auto;
box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}
.calculator-inputs {
display: grid;
grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
gap: 15px;
margin-bottom: 20px;
}
.input-group {
display: flex;
flex-direction: column;
}
.input-group label {
margin-bottom: 5px;
font-weight: bold;
color: #333;
}
.input-group input {
padding: 10px;
border: 1px solid #ddd;
border-radius: 4px;
font-size: 1rem;
}
#evaporation-calculator button {
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
cursor: pointer;
font-size: 1rem;
transition: background-color 0.3s ease;
}
#evaporation-calculator button:hover {
background-color: #0056b3;
}
#result {
margin-top: 20px;
padding: 15px;
background-color: #e9ecef;
border-radius: 4px;
text-align: center;
font-size: 1.1rem;
color: #333;
min-height: 50px; /* To prevent layout shifts */
}
function calculateEvaporation() {
var surfaceArea = parseFloat(document.getElementById("surfaceArea").value);
var windSpeed = parseFloat(document.getElementById("windSpeed").value);
var airTemperature = parseFloat(document.getElementById("airTemperature").value);
var waterTemperature = parseFloat(document.getElementById("waterTemperature").value);
var relativeHumidity = parseFloat(document.getElementById("relativeHumidity").value);
var timePeriod = parseFloat(document.getElementById("timePeriod").value);
var resultDiv = document.getElementById("result");
if (isNaN(surfaceArea) || isNaN(windSpeed) || isNaN(airTemperature) || isNaN(waterTemperature) || isNaN(relativeHumidity) || isNaN(timePeriod)) {
resultDiv.innerHTML = "Please enter valid numbers for all fields.";
return;
}
if (surfaceArea <= 0 || windSpeed < 0 || airTemperature < -273.15 || waterTemperature < -273.15 || relativeHumidity 100 || timePeriod <= 0) {
resultDiv.innerHTML = "Please enter valid physical values for all fields.";
return;
}
// This calculator uses a simplified empirical formula (e.g., Penman-Monteith or similar simplified versions)
// For accurate scientific calculations, more complex models and data (like solar radiation, vapor pressure deficit) are needed.
// This implementation uses a basic approach that considers key factors.
// Constants and intermediate calculations (example values, these might need adjustment based on specific models)
var a = 0.0001; // Empirical coefficient for wind effect
var b = 0.1; // Empirical coefficient for temperature difference
var c = 0.005; // Empirical coefficient for humidity effect
// Calculate vapor pressure deficit (difference between saturation vapor pressure and actual vapor pressure)
// Simplified saturation vapor pressure calculation (August-Roche-Magnus formula approximation)
var saturationVaporPressureAir = 0.6108 * Math.exp((17.27 * airTemperature) / (airTemperature + 237.3));
var saturationVaporPressureWater = 0.6108 * Math.exp((17.27 * waterTemperature) / (waterTemperature + 237.3));
var actualVaporPressure = saturationVaporPressureAir * (relativeHumidity / 100);
var vaporPressureDeficit = saturationVaporPressureWater – actualVaporPressure;
if (vaporPressureDeficit < 0) vaporPressureDeficit = 0; // Ensure deficit is not negative
// Wind speed influence
var windFactor = 1 + a * windSpeed;
// Temperature difference influence
var tempDiffFactor = 1 + b * (waterTemperature – airTemperature);
if (tempDiffFactor < 0) tempDiffFactor = 0; // Ensure factor is not negative
// Humidity influence (inversely related, but already handled by Vapour Pressure Deficit)
// Direct humidity effect can be complex, often incorporated into VPD.
// For simplicity here, we mainly rely on VPD.
// Evaporation rate (e.g., mm/hour) – simplified empirical model
// This is a conceptual model. Real models are more complex.
// A very basic representation: Evaporation is proportional to VPD, wind, and surface area, and inversely to external factors not explicitly modeled here.
// Let's use a linear combination for demonstration purposes.
// Conceptual formula: E = k * SA * (VPD + tempDiffFactor) * windFactor * timePeriod
// Where k is another constant and units need careful consideration.
// For this example, we will output total water loss in Liters.
// Conversion: 1 mm of water over 1 m² is 1 Liter.
// Let's assume a base evaporation rate factor.
var evaporationRateConstant = 0.2; // mm/hour for baseline conditions (hypothetical)
var totalEvaporationRate_mm_hr = evaporationRateConstant * vaporPressureDeficit * windFactor * tempDiffFactor;
// Ensure evaporation rate is not negative (e.g., if humidity is very high and water is cooler than air)
if (totalEvaporationRate_mm_hr < 0) {
totalEvaporationRate_mm_hr = 0;
}
// Total evaporation in mm over the time period
var totalEvaporation_mm = totalEvaporationRate_mm_hr * timePeriod;
// Total water loss in Liters (1 mm over 1 m² = 1 Liter)
var totalWaterLoss_Liters = totalEvaporation_mm * surfaceArea;
resultDiv.innerHTML = "Estimated Evaporation Rate: " + totalEvaporationRate_mm_hr.toFixed(3) + " mm/hour" +
"Total Water Loss over " + timePeriod + " hours: " + totalWaterLoss_Liters.toFixed(2) + " Liters";
}
Understanding Evaporation Rate
Evaporation is the process by which water changes from a liquid to a gas or vapor. It's a crucial component of the Earth's water cycle, affecting everything from agricultural water management to the water levels in reservoirs and swimming pools. Calculating the rate of evaporation helps in predicting water loss and implementing strategies to conserve water or manage its availability.
Factors Influencing Evaporation
Several environmental factors significantly influence how quickly water evaporates:
Surface Area: A larger surface area exposed to the air will result in a higher evaporation rate. More water molecules are in contact with the air, increasing the potential for vaporization.
Temperature: Both air and water temperature play a vital role. Higher temperatures provide more kinetic energy to water molecules, making it easier for them to escape into the atmosphere as vapor. Warmer water also tends to hold more moisture in the air above it.
Wind Speed: Wind helps to remove the layer of humid air that forms just above the water surface. By replacing this humid air with drier air, wind increases the vapor pressure gradient and thus accelerates evaporation.
Relative Humidity: This measures how much water vapor is already present in the air compared to the maximum it can hold at a given temperature. High relative humidity means the air is already saturated, slowing down evaporation. Conversely, dry air (low humidity) encourages more rapid evaporation.
Solar Radiation: While not directly included in this simplified calculator, solar radiation is a primary energy source that heats water, directly increasing its temperature and promoting evaporation.
How the Calculator Works (Simplified Model)
This calculator provides an estimated evaporation rate using a simplified empirical formula. It considers the primary factors: surface area, wind speed, air temperature, water temperature, and relative humidity. The calculation involves estimating the vapor pressure deficit (VPD) – the difference between how much moisture the air *could* hold at saturation and how much it *actually* holds. A higher VPD generally leads to greater evaporation. The calculator then modifies this based on wind speed and the temperature difference between water and air. The result is presented as an evaporation rate per hour and the total volume of water lost over a specified period.
Note: For precise scientific or industrial applications, more complex models like the Penman-Monteith equation are often used, requiring additional data such as solar radiation, atmospheric pressure, and potentially more detailed aerodynamic and energy balance components.
Example Calculation
Let's consider a small pond with the following conditions:
Surface Area: 50 m²
Wind Speed: 2.5 m/s
Air Temperature: 28°C
Water Temperature: 25°C
Relative Humidity: 60%
Time Period: 12 hours
Plugging these values into the calculator:
The calculator estimates an average evaporation rate and then calculates the total water loss. For these inputs, you might see results like:
Estimated Evaporation Rate: Approximately 0.350 mm/hour
Total Water Loss over 12 hours: Approximately 210.00 Liters
This means that over 12 hours, the pond could lose roughly 210 liters of water due to evaporation under these specific conditions.