Water evaporates constantly from lakes, ponds, swimming pools, and other exposed surfaces. Understanding how quickly this occurs is useful for farmers managing irrigation, engineers designing reservoirs, and homeowners maintaining pools or ornamental ponds. Although evaporation is a complex process influenced by many variables, this calculator provides a simple estimation method based on commonly measured factors: temperature, humidity, wind speed, and surface area.
At its core, evaporation occurs when water molecules at the surface gain enough energy to break free from the liquid and disperse into the air. Warmer temperatures supply more energy, while lower humidity encourages the vapor to remain in the atmosphere rather than condense back into the water. Wind removes humid air from the surface, replacing it with drier air and increasing the evaporation rate. These principles form the basis of the simplified formula used here.
Many scientific models exist for predicting evaporation, ranging from the Penman equation to mass transfer approaches. To keep this calculator accessible, we use a streamlined expression:
Here represents the evaporation rate in millimeters per day, is wind speed in meters per second, is air temperature in degrees Celsius, and is relative humidity as a percentage. The constants provide a rough linear approximation that captures how evaporation increases with temperature and wind while decreasing with humidity.
After calculating , we convert it to liters of water lost per day by multiplying by the surface area in square meters. One millimeter over one square meter equals one liter, so the total volume lost is simply , where is the area.
The output provides an estimated evaporation rate in both millimeters per day and liters per day. Because this model is simplified, real-world rates may differ, especially in extreme climates or where heat sources like pumps and fountains increase turbulence. Nonetheless, the estimate gives a sense of daily water loss for planning purposes. If the result seems unusually high or low, consider how shade, rainfall, or evaporation-reducing covers might alter the actual rate.
The table below shows example rates for various conditions to highlight how each factor contributes:
| Temperature (°C) | Humidity (%) | Wind (m/s) | E (mm/day) |
|---|---|---|---|
| 20 | 50 | 1 | 4.0 |
| 30 | 40 | 3 | 10.2 |
| 35 | 20 | 5 | 18.0 |
Farmers often track evaporation to adjust irrigation schedules. If a crop’s field loses ten millimeters of water per day, they know to replace that amount through watering to maintain healthy soil moisture. Pool owners use evaporation estimates to determine how frequently to top off their pools, while engineers rely on evaporation data when designing reservoirs or planning for drought conditions. In all these cases, even a rough approximation can guide decision-making.
Beyond quantity, evaporation also influences water quality. As water evaporates, dissolved minerals and contaminants become more concentrated. Understanding the rate of evaporation helps maintain balanced chemistry, especially in pools or artificial ponds where high mineral buildup can cause scaling or algae growth.
This calculator intentionally streamlines the process to keep it user-friendly. In reality, evaporation depends on additional factors such as air pressure, solar radiation, and the water’s own temperature. Advanced models incorporate these variables to provide more precise estimates. However, the simplified formula works surprisingly well for quick assessments and for exploring how changes in temperature, humidity, or wind might affect overall water loss.
Because conditions can vary widely throughout the day, you may want to average multiple readings or use typical daytime values for the best approximation. Periodically verifying the estimate with real measurements—such as monitoring water level drop over a known time—helps fine-tune the model to your specific location.
To use the tool, enter the surface area of the water body in square meters, the current air temperature, relative humidity, and average wind speed. After clicking Estimate, the script computes the evaporation rate using the formula above. Results appear below the form. If you notice large daily losses, consider using covers, windbreaks, or shade to reduce evaporation, or explore whether the measurement values accurately reflect your environment.
Understanding evaporation helps you plan for water conservation and budget for replenishment. It also aids in anticipating how quickly pesticides or fertilizer concentrations might increase in a pond or reservoir. The more you observe your own setup, the better you can adjust the model for local conditions.
Researchers continue to refine evaporation models with satellite data and improved weather monitoring. If you need highly precise values for a scientific project, you might consult detailed meteorological formulas or local climate specialists. For everyday planning, though, this calculator offers a practical estimate with just a few inputs.
Whether you manage a backyard pond or a large agricultural reservoir, paying attention to evaporation ensures efficient water use. By accounting for weather conditions and site-specific factors, you can maintain healthy ecosystems, prevent waste, and anticipate how often you need to replenish your water supply.
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