How to Use This Calculator

This calculator helps you estimate potential evapotranspiration and irrigation requirements based on your local climate data. Follow these steps to get accurate results.

Step-by-Step Instructions

Enter the air temperature at a standard height (usually 2 meters above ground)
Input the relative humidity percentage observed during the measurement period
Provide the wind speed at standard measurement height (usually 2 meters)
Enter solar radiation values if available, or use typical values for your region
Specify your location's latitude and altitude for accurate calculations
Select the month to account for seasonal variations in day length
Choose the calculation method based on available data: Penman-Monteith (most accurate with complete data), Thornthwaite (requires temperature only), Blaney-Criddle (requires temperature and wind), or Radiation (uses solar radiation primarily)
Click Calculate to generate results
Review daily, monthly, and annual PET values
Export results to CSV for further analysis or record keeping

Applications of Evaporation Rate Calculation

Evaporation rate calculations are essential in many fields and applications. Understanding PET helps professionals make informed decisions about water management and resource allocation.

Agricultural Irrigation Planning

Calculate precise irrigation requirements for crops to optimize water use and reduce costs while maintaining yield. Helps schedule irrigation timing and determine water application rates.

例: Crop water demand calculation, Irrigation scheduling, Water conservation

Hydrological Studies

Estimate water availability and runoff in river basins, watersheds, and aquifers. Essential for water balance calculations and sustainable groundwater management.

例: Watershed analysis, Groundwater recharge estimation, Water availability assessment

Environmental and Climate Monitoring

Track changes in evaporation patterns to assess climate impacts and drought conditions. Monitor water stress in ecosystems and plan conservation strategies.

例: Drought monitoring, Climate impact assessment, Ecosystem water stress analysis

Landscape and Turf Management

Design efficient irrigation systems for golf courses, parks, and gardens. Calculate water requirements for maintaining healthy vegetation with minimal waste.

例: Golf course irrigation, Park landscape design, Garden water planning

Water Resources Engineering

Plan water supply systems and reservoirs based on accurate evaporation estimates. Design dams and water distribution systems considering evaporation losses.

例: Reservoir design, Water supply planning, Distribution system efficiency

Soil and Water Conservation

Develop strategies to minimize water loss and maintain soil moisture. Design conservation practices based on local evaporation patterns and water availability.

例: Mulching strategy, Windbreak design, Soil conservation planning

Calculation Formulas

Different methods calculate PET based on available meteorological data. Each method has different accuracy and data requirements.

Penman-Monteith Method (FAO-56)

ET₀ = [0.408 × Δ × (Rₙ - G) + γ × (Cn/(T+273)) × u₂ × (eₛ - ea)] / [Δ + γ(1 + Cd × u₂)]

Where ET₀ = reference evapotranspiration (mm/day), Δ = slope of saturation vapor pressure curve, Rₙ = net radiation, G = soil heat flux, γ = psychrometric constant, u₂ = wind speed at 2m, eₛ = saturation vapor pressure, ea = actual vapor pressure, T = mean temperature

Thornthwaite Method

PET = 16 × (10T/I)^a × (N/12) × (Nd/30)

Where PET = potential evapotranspiration, T = mean monthly temperature, I = annual heat index, a = empirical coefficient, N = number of days in month, Nd = average day length

Blaney-Criddle Method

ET = KT × p × (0.46 × T + 8.13)

Where ET = evapotranspiration (mm/day), KT = crop coefficient, T = mean daily temperature (°C), p = mean daily percentage of annual daytime hours

Radiation Method

ET₀ = 0.408 × Δ × Rₙ / (Δ + γ)

Where ET₀ = reference evapotranspiration, Δ = slope of saturation vapor pressure curve, Rₙ = net radiation (MJ/m²/day), γ = psychrometric constant

Factors Affecting Evaporation

Multiple meteorological and environmental factors influence evaporation rates. Understanding these factors helps in better water management and prediction.

Temperature: Higher temperatures increase molecular motion and evaporation rates significantly
Humidity: Lower relative humidity increases evaporation potential as air can hold more moisture
Wind Speed: Faster winds remove saturated air layers near surfaces, increasing evaporation
Solar Radiation: More solar energy provides power for evaporation and heating of water
Atmospheric Pressure: Lower pressure increases evaporation rate as vapor molecules escape more easily
Water Availability: Soil moisture and water surface conditions limit actual evaporation
Vegetation Type: Different plants have different transpiration rates based on leaf area and structure
Soil Properties: Soil texture, organic matter, and color affect surface evaporation and heat absorption

Frequently Asked Questions

Q: What is the difference between PET and AET?

A: PET (Potential Evapotranspiration) is the maximum water loss possible under ideal conditions, while AET (Actual Evapotranspiration) is the real water loss considering actual water availability. AET is always less than or equal to PET.

Q: Which calculation method should I use?

A: Use Penman-Monteith if you have complete meteorological data (temperature, humidity, wind, radiation). Use Thornthwaite if only temperature is available. Use Blaney-Criddle for limited data scenarios. Use Radiation method if solar radiation data is the most reliable.

Q: How often should I update irrigation based on PET?

A: Update irrigation schedules weekly or bi-weekly based on weather conditions and accumulated PET values. During growing season, check PET calculations 2-3 times per week for optimal irrigation timing.

Q: What does crop coefficient (Kc) mean?

A: Crop coefficient is the ratio of actual crop evapotranspiration to reference evapotranspiration. It varies with crop type and growth stage, typically ranging from 0.3-1.2 for different crops.

Q: Why is water deficit important?

A: Water deficit represents the amount of water needed to supplement natural precipitation for full crop growth. It helps determine total irrigation requirement and water allocation for planning.

Q: How accurate are PET calculations?

A: Penman-Monteith method has ±5-10% accuracy. Thornthwaite and Blaney-Criddle methods have ±15-20% accuracy. Accuracy depends on input data quality and local climate variability.

Q: What solar radiation values should I use?

A: Typical solar radiation ranges from 5-30 MJ/m²/day depending on latitude, season, and weather. Check local meteorological stations or use standard values for your region.

Q: How does latitude affect evaporation calculation?

A: Latitude affects day length and solar angle, which influence solar radiation and temperature. Higher latitudes have larger seasonal variations in day length and PET.

Q: What is the impact of wind speed on PET?

A: Wind speed increases evaporation by removing saturated air layers. Areas with higher wind speeds typically have 20-30% higher evaporation rates compared to calm areas.

Q: Can I use this calculator for indoor plant irrigation?

A: This calculator is designed for outdoor conditions. Indoor PET is much lower due to stable conditions, controlled humidity, and lack of wind. Reduce values by 50-70% for indoor applications.

Evaporation Rate Calculator

Input Parameters

About Evaporation Rate Calculator

What is Potential Evapotranspiration (PET)?

Key Components of Evaporation

Why PET Matters