Derive Reference Potential Evapotranspiration from Potential Evapotranspiration

Asked by: Kim Hill

How is reference evapotranspiration calculated?

where ETo = reference evapotranspiration rate (mm d-1), T = mean air temperature (°C), and u2 = wind speed (m s-1) at 2 m above the ground. Equation 3 can be applied using hourly data if the constant value “900” is divided by 24 for the hours in a day and the Rn and G terms are expressed as MJ m-2 h-1.

What is the difference between reference evapotranspiration and potential evapotranspiration?

Reference evapotranspiration is that from a grass surface that is well-watered. Potential evapotranspiration is that from a surface that has unlimited water (such as a lake).

How do you calculate potential evapotranspiration from actual evapotranspiration?

it is simple… ETc=Kc. ET0; where ETc is actual evapotranspiration, Kc is crop coefficient and ET0 is Referece evapotranspiration. You might get Kc values based on the specified crop as well as its stage of growth.

What are the three methods to determine potential evapotranspiration?

Methods for evaluating evapotranspiration can be divided into three categories: hydrologic or water balance methods, analytical methods based on climate variables, and empirical estimates. The water balance method to determine Ev consists of catchment hydrology, soil water depletion sampling, and lysimetry testing.

What is reference evaporation?

The reference evaporation, a concept introduced in the 1990’s by the Food and Agriculture Organization (FAO) and presented in this paper, defines the evaporation potential of standard vegetation with an abundant water supply.

What is reference and crop evapotranspiration?

Reference crop evapotranspiration or reference evapotranspiration, denoted as ETo or ETref, is the estimation of the evapotranspiration from the “reference surface.” The reference surface is a hypothetical grass reference crop with an assumed crop height of 0.12 m, a fixed surface resistance of 70 s/m and an albedo of

What is the difference between AET and PET?

PET is a function of relative humidity, solar radiation, water availability, wind, and temperature. AET or ET is how much water is going to evaporate when there is a water limitation. AET is a function of vegetation cover, root, and soil. Usually, PET is larger than ET.

What is the difference between ET and PET?

Potential evapotranspiration (PET) is defined as the maximum amount of water that can be removed from a land surface through evapotranspiration (ET) as sum of both evaporation and transpiration given abundant supply of soil moisture. In other words, the removal of water by ET depends only upon the available energy.

What is potential evapotranspiration in hydrology?

Potential evapotranspiration (Ep) is the water vapor flux under ideal conditions of complete ground cover by plants, uniform plant height and leaf coverage, and an adequate water supply; From: Trace Fossils, 2007.

Why the value of AET is less than pet?

If the water supply to the plant is adequate, soil moisture will be at field capacity then, the ratio of AET to PET = 1. If the water supply to the plant is inadequate, then the ratio of AET to PET is less than 1. In clayey soils, AET/PET is almost equal to 1.

What is the Penman Monteith equation used for?

The Penman–Monteith equation is widely used in land process modeling to estimate vegetation transpiration or soil evaporation because it requires only conventional observations as input and does not require input from two levels.

What is the meaning of actual evapotranspiration?

Actual Evapotranspiration (ETa) is the quantity of water that is removed from a surface due to the processes of evaporation and transpiration and is measured in millimeters (mm). ETa is scene-based and derived from the Landsat Level-2 Surface Temperature products.

What is ETo and ETc?

The estimated crop water requirement (ETc) for high growth rates is obtained by multiplying the specific crop coefficient (Kc) by reference evapotranspiration (ETo). ie. ETc = ETo x Kc.

What is the importance of reference evapotranspiration?

Actual evapotranspiration is a key factor of hydrological cycle and agricultural water management. Therefore, in a sense, the accurate forecast for reference evapotranspiration plays an important role in understanding the hydrological cycle, especially in planning and managing irrigation practices.

What are the units of ETo?

0.7 || 0.6 || ETo units can be in ‘English’ (inches) or Metric (millimeters). Many factors can affect the rate of evaporation from an open body of water; depth of water, area of the water, temperature of water, topography and vegetation surrounding the body of water, etc.

How is evaporation rate calculated?

The equation states that, the evaporation rate, W = (95+0.425*V)*(Pw-Pa)/Y, where W is the Evaporation rate in lb/h-ft²; V is the air velocity at water surface; ft/min; Pw is the saturation vapor pressure at water temperature, in. Hg; Pa is saturation vapor pressure at air dew point, in.

How is Penman Monteith equation calculated?

Δ = (0.00815 T_a + 0.8912)⁷ = 1.447 mb/°C. The vapor pressure deficit is (Ponce, 2014: Section 2.2): (e_s – e_a) ≅ (e_o – e_a) = e_o [ 1 – (φ / 100) ] = 23.37 [ 1 – (70 / 100)] = 7.01 mb.

What is the normal evapotranspiration rate?

Estimates of the mean annual evapotranspiration have been derived from hydrologic budgets for each State. These estimates indicate that statewide evapotranspiration within the conterminous United States ranges from about 10 inches per year in the semiarid Southwest to about 35 inches per year in the humid Southeast.

What is a lysimeter and how does it work?

A lysimeter (from Greek λύσις (loosening) and the suffix -meter) is a measuring device which can be used to measure the amount of actual evapotranspiration which is released by plants (usually crops or trees).

How is lysimeter measured?

A lysimeter is a measuring device which can be used to measure the actual evapotranspiration which is released by plants. By recording the amount of precipitation that an area receives and the amount lost through the soil, the amount of water lost to evapotranspiration can be calculated.

What is lysimeter experiment?

Lysimeter experiments were conducted to determine the ability of different soils to reduce levels of biochemical oxygen demand (BOD) and concentrations of molybdate reactive phosphorus (MRP) and ammonium-N (NH4(+)-N) in dirty water and the impact of applications on nitrate leaching.