Evaporation Rate Calculator

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Evaporation Rate Calculator

Understanding Evaporation Rate

Evaporation is a fundamental process in the water cycle, where liquid water turns into vapor and rises into the atmosphere. The rate at which this occurs is influenced by several environmental factors. Understanding and calculating this rate is crucial for various applications, including water resource management, agriculture, climate modeling, and even understanding the drying process of surfaces.

Factors Affecting Evaporation Rate:

  • Surface Area: A larger exposed surface area of water will lead to a higher rate of evaporation, as more molecules are available to transition into the gaseous state.
  • Water Temperature: Warmer water molecules have more kinetic energy, making it easier for them to escape the liquid surface and become vapor. Therefore, higher water temperatures increase the evaporation rate.
  • Air Temperature: Similar to water temperature, warmer air can hold more moisture. A higher air temperature creates a greater vapor pressure deficit between the water surface and the air above it, driving evaporation.
  • Relative Humidity: This measures the amount of water vapor in the air compared to the maximum it can hold at a given temperature. High humidity means the air is already saturated with water vapor, reducing the driving force for evaporation. Conversely, low humidity accelerates evaporation.
  • Wind Speed: Wind plays a vital role by removing humid air from just above the water surface and replacing it with drier air. This maintains a steeper vapor pressure gradient, enhancing the evaporation rate.

How the Calculator Works:

This calculator utilizes a simplified model to estimate the potential evaporation rate. It considers the key environmental factors listed above. While complex atmospheric physics can involve intricate equations, this tool provides a practical approximation. The formula used is based on principles that relate the vapor pressure deficit (influenced by water temperature, air temperature, and humidity) and the effect of wind speed on mass transfer.

The calculated result will be presented in liters per day per square meter (L/day/m²), offering a practical measure of how much water might evaporate from a given surface area under the specified conditions.

Example Calculation:

Let's consider a scenario where we have a water reservoir with a surface area of 100 m². The water temperature is 25°C, and the air temperature is 30°C. The relative humidity is 60%, and the wind speed is 2.5 m/s.

Inputs:

  • Surface Area: 100 m²
  • Water Temperature: 25 °C
  • Air Temperature: 30 °C
  • Relative Humidity: 60 %
  • Wind Speed: 2.5 m/s

Based on these inputs, the calculator will process the data using its internal algorithms to estimate the evaporation rate.

function calculateEvaporation() { var surfaceArea = parseFloat(document.getElementById("surfaceArea").value); var waterTemperature = parseFloat(document.getElementById("waterTemperature").value); var airTemperature = parseFloat(document.getElementById("airTemperature").value); var humidity = parseFloat(document.getElementById("humidity").value); var windSpeed = parseFloat(document.getElementById("windSpeed").value); var resultDiv = document.getElementById("result"); if (isNaN(surfaceArea) || isNaN(waterTemperature) || isNaN(airTemperature) || isNaN(humidity) || isNaN(windSpeed)) { resultDiv.innerHTML = "Please enter valid numbers for all fields."; return; } if (humidity 100) { resultDiv.innerHTML = "Humidity must be between 0 and 100%."; return; } // Simplified Penman-Monteith equation components (for illustrative purposes) // This is a highly simplified version. Real Penman-Monteith is more complex. // Constants are approximate and may vary based on specific empirical studies. // Saturation vapor pressure (kPa) – Tetens' equation (simplified) var saturationVaporPressureWater = 0.6108 * Math.exp((17.27 * waterTemperature) / (waterTemperature + 237.3)); var saturationVaporPressureAir = 0.6108 * Math.exp((17.27 * airTemperature) / (airTemperature + 237.3)); // Actual vapor pressure (kPa) var actualVaporPressure = (humidity / 100) * saturationVaporPressureAir; // Vapor pressure deficit (kPa) var vpd = saturationVaporPressureWater – actualVaporPressure; // Aerodynamic resistance (simplified, depends on wind) // This is a very rough approximation. Real resistance terms are more involved. var aerodynamicResistance = 200 / (windSpeed + 0.5); // Example: higher wind, lower resistance // Radiation term (simplified – often a major component of Penman-Monteith) // For this simplified example, we'll assume a baseline and adjust slightly var radiationFactor = 1.0; // Placeholder for complex radiation calculations // Evaporation rate (mm/day) – very rough approximation combining VPD and wind effects // The formula below is illustrative and not a precise physical model. // Real Penman-Monteith incorporates net radiation, psychrometric constant, etc. var evaporationRate_mm_per_day = (0.05 * vpd + 0.005 * windSpeed * vpd) * radiationFactor; // Highly simplified // Ensure evaporation is not negative if (evaporationRate_mm_per_day < 0) { evaporationRate_mm_per_day = 0; } // Convert mm/day to liters/day/m² // 1 mm of water over 1 m² is 1 liter var evaporationRate_L_per_day_per_m2 = evaporationRate_mm_per_day; // Total evaporation for the given surface area var totalEvaporation_L_per_day = evaporationRate_L_per_day_per_m2 * surfaceArea; resultDiv.innerHTML = "

Estimated Evaporation Rate:

" + "Potential Evaporation Rate: " + evaporationRate_L_per_day_per_m2.toFixed(2) + " L/day/m²" + "Total Evaporation from Surface: " + totalEvaporation_L_per_day.toFixed(2) + " L/day"; }

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