Dalton-Type Equation Calculator

Dalton-Type Equation:

\[ E_{lake} = K \times f_u \times (e_s - e_a) \]

Coefficient (K):

Wind Speed Correction Factor (f_u):

Saturation Vapour Pressure (e_s):

mm Hg

Actual Vapour Pressure (e_a):

mm Hg

Lake Evaporation (E_lake):

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1. What is the Dalton-Type Equation?

The Dalton-Type Equation estimates lake evaporation based on meteorological parameters. It provides a fundamental approach to calculate evaporation rates from water surfaces using vapour pressure differences and wind effects.

2. How Does the Calculator Work?

The calculator uses the Dalton-Type equation:

\[ E_{lake} = K \times f_u \times (e_s - e_a) \]

Where:

\( E_{lake} \) — Lake Evaporation (mm/day)
\( K \) — Coefficient (dimensionless)
\( f_u \) — Wind Speed Correction Factor (dimensionless)
\( e_s \) — Saturation Vapour Pressure at Water Surface (mm Hg)
\( e_a \) — Actual Vapour Pressure in Air (mm Hg)

Explanation: The equation accounts for the driving force of evaporation (vapour pressure deficit) and the enhancing effect of wind on the evaporation process.

3. Importance of Lake Evaporation Calculation

Details: Accurate lake evaporation estimation is crucial for water resource management, hydrological modeling, climate studies, and irrigation planning. It helps in understanding water balance of lakes and reservoirs.

4. Using the Calculator

Tips: Enter all required parameters with appropriate units. Ensure vapour pressure values are in mm Hg. All values must be positive, with saturation vapour pressure typically greater than actual vapour pressure.

5. Frequently Asked Questions (FAQ)

Q1: What are typical values for coefficient K?
A: Coefficient K typically ranges from 0.4 to 0.7, depending on local conditions and specific formulations of the Dalton equation.

Q2: How is wind speed correction factor determined?
A: The wind speed correction factor is usually derived from empirical relationships between wind speed and evaporation rates, often expressed as a function of wind speed.

Q3: What units should be used for vapour pressure?
A: While mm Hg is traditional, the equation works with any consistent pressure units as long as both e_s and e_a use the same units.

Q4: What are limitations of the Dalton-Type equation?
A: The equation may not account for all meteorological factors and may require local calibration. It assumes steady-state conditions and may not capture diurnal variations well.

Q5: How does this relate to pan evaporation measurements?
A: Lake evaporation is typically less than pan evaporation due to different energy budgets. Pan coefficients are often used to convert pan evaporation to lake evaporation.