Evaporation Loss Per Day Calculator

Rohwer's Formula:

\[ E = C' \times (1.465 - (0.00732 \times P_a)) \times (0.44 + (0.0732 \times u)) \times (V - v) \]

Rohwer's Formula Constant (C'):

Atmospheric Pressure (Pₐ):

cm Hg

Mean Wind Velocity (u):

m/s

Maximum Vapour Pressure (V):

cm Hg

Actual Vapour Pressure (v):

cm Hg

Evaporation Loss Per Day (E):

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1. What is Rohwer's Formula?

Rohwer's Formula is an empirical equation used to estimate daily evaporation loss from water surfaces. It accounts for atmospheric pressure, wind velocity, and vapour pressure differences to provide accurate evaporation rate estimates.

2. How Does the Calculator Work?

The calculator uses Rohwer's Formula:

\[ E = C' \times (1.465 - (0.00732 \times P_a)) \times (0.44 + (0.0732 \times u)) \times (V - v) \]

Where:

\( E \) — Evaporation loss per day (m)
\( C' \) — Rohwer's Formula Constant
\( P_a \) — Atmospheric pressure (cm Hg)
\( u \) — Mean wind velocity (m/s)
\( V \) — Maximum vapour pressure (cm Hg)
\( v \) — Actual vapour pressure (cm Hg)

Explanation: The formula calculates evaporation based on pressure conditions, wind speed, and the difference between maximum and actual vapour pressures.

3. Importance of Evaporation Loss Calculation

Details: Accurate evaporation loss calculation is crucial for water resource management, irrigation planning, reservoir operations, and climate studies. It helps in predicting water availability and designing efficient water storage systems.

4. Using the Calculator

Tips: Enter all required values with appropriate units. Ensure atmospheric pressure, maximum vapour pressure, and actual vapour pressure are in cm Hg, wind velocity in m/s, and the constant is the appropriate empirical value for your location.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical value for Rohwer's constant?
A: The constant typically ranges from 0.4 to 0.8 depending on local conditions and should be calibrated for specific locations.

Q2: How does wind velocity affect evaporation?
A: Higher wind velocities increase evaporation rates by removing saturated air from the water surface and replacing it with drier air.

Q3: Why is vapour pressure difference important?
A: The difference between maximum and actual vapour pressure drives the evaporation process - larger differences result in higher evaporation rates.

Q4: When is this formula most accurate?
A: The formula works best for open water surfaces under moderate climatic conditions and may require adjustment for extreme environments.

Q5: Can this formula be used for all water bodies?
A: While generally applicable, the formula may need calibration for specific water body characteristics such as size, depth, and surrounding topography.