1. What is the Surface Water Evaporation Rate Equation?

The Surface Water Evaporation Rate equation estimates the daily evaporation rate from water surfaces based on wind speed and vapor pressure difference. It's commonly used in hydrology, agriculture, and environmental engineering to predict water loss from lakes, reservoirs, and other water bodies.

2. How Does the Calculator Work?

The calculator uses the evaporation rate equation:

Where:

• \( ER \) — Evaporation Rate (mm per day)
• \( W \) — Wind Speed (miles per hour)
• \( e_s \) — Saturation Vapor Pressure (kPa)
• \( e_d \) — Actual Vapor Pressure (kPa)

Explanation: The equation accounts for both wind-driven evaporation and the vapor pressure deficit, which is the difference between the maximum possible vapor pressure and the actual vapor pressure in the air.

3. Importance of Evaporation Rate Calculation

Details: Accurate evaporation rate estimation is crucial for water resource management, irrigation planning, reservoir operation, climate studies, and environmental impact assessments. It helps predict water losses and optimize water usage in various applications.

4. Using the Calculator

Tips: Enter wind speed in miles per hour, and both vapor pressures in kPa. Ensure that saturation vapor pressure is greater than or equal to actual vapor pressure for meaningful results. All values must be non-negative.

5. Frequently Asked Questions (FAQ)

Q1: What factors affect evaporation rate?
A: Key factors include temperature, humidity, wind speed, solar radiation, and water surface area. This equation focuses on wind speed and vapor pressure difference.

Q2: How is vapor pressure measured?
A: Saturation vapor pressure depends on temperature, while actual vapor pressure can be calculated from relative humidity and temperature measurements.

Q3: What are typical evaporation rates?
A: Rates vary widely by climate: 2-4 mm/day in temperate regions, 5-10 mm/day in arid regions, and up to 15 mm/day in hot desert conditions.

Q4: Can this equation be used for all water bodies?
A: It works best for open water surfaces. For vegetation-covered surfaces or small ponds, additional factors may need consideration.

Q5: How accurate is this evaporation model?
A: It provides reasonable estimates for general applications but may need calibration for specific locations or extreme weather conditions.