What is the reference 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 find reference evapotranspiration?
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.
How do you calculate reference crop evapotranspiration?
Crop evapotranspiration is calculated by multiplying ETo by Kc, a coefficient expressing the difference in evapotranspiration between the cropped and reference grass surface.
How do you calculate monthly reference evapotranspiration?
A mean monthly evaporation from reservoirs, ponds, and lakes are also estimated by multiplying the monthly ETo by 1.2. Estimate of monthly crop evapotranspiration is made by multiplying monthly ETo by corresponding monthly crop coefficients.
What is reference crop evapotranspiration ETo?
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 …
Why is reference evapotranspiration important?
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 is reference crop ET?
Reference crop evapotranspiration (ETo)
The evapotranspiration rate from a reference surface, not short of water, is called the reference crop evapotranspiration or reference evapotranspiration and is denoted as ETo. The reference surface is a hypothetical grass reference crop with specific characteristics.
What is ETc and ETo?
ETc = crop evapotranspiration/Crop water requirement (mm day-1), ETo = reference evapotranspiration (mm day-1), Kc = crop coefficient. The daily ETc computed were summed for different growth stages of crop and total seasonal crop water was determined for wheat and maize crops.
What is ETo in rainfall?
ETo specifically refers to evapotranspiration from a reference stand of actively growing, well-watered grass, 120mm in height. For practical purposes, ETo provides a workable representation of the water requirements of good productive pasture on an irrigated farm.
What is ETo in agriculture?
The reference evapotranspiration (ETo) is defined as the loss of water to the atmosphere by evaporation and transpiration from an extended surface of 8-12 cm tall green grass cover, usually a well-watered, actively growing and completely shading the ground.
What is the importance of reference evapotranspiration?
What are the types of evapotranspiration?
Types of evapotranspiration • Evapotranspiration may be classified as: • 1. Potential evapotranspiration (PET). 2. Actual evapotranspiration (AET).
What factors affect evapotranspiration?
The principal weather parameters affecting evapotranspiration are radiation, air temperature, humidity and wind speed.
How do you calculate ET?
Generally, what you’ll do is add the highest temperature during a 24-hour period to the lowest temperature during that same period, then divide that sum by two. This will give you a good estimate for the average temperature during that time.
What is ETo value?
ETo values can be considered equal to evaporation from a large body of water, such as a pond or lake. However, for smaller, shallower bodies of water this relationship does not apply. Many factors affect lake/pond evaporation including surface area, depth, water temperature, and turbidity.
How is ETo measured?
ETo rates are typically measured in millimetres per day (mm/day) and are highest in the summer months and comparatively lower in spring and autumn.
What is the importance of evapotranspiration?
Evapotranspiration is an important process in the water cycle because it is responsible for 15% of the atmosphere’s water vapor. Without that input of water vapor, clouds couldn’t form and precipitation would never fall. Evapotranspiration is the combined name for the processes of evaporation and transpiration.
What are types of evapotranspiration?
What can cause decreased evapotranspiration?
The decrease of ET0 is mainly caused by wind speed reduction because of its high sensitivity and significant decreasing trend, to a less extent by decreasing in the net solar radiation over the catchment. The contribution from wind speed to decreased ET0 increased from 50 to 76.1% during the past 49 years.
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.
How do you calculate ET tube length?
Pediatric tubes are sized using the equation: size = ((age/4) +4) for uncuffed ETTs, with cuffed tubes being one-half size smaller. [6] Typically a pediatric ETT is taped at a depth of 3 x the tube size in a child (i.e., a 4.0 ETT commonly gets taped at around 12cm depth).
What are two sources of evapotranspiration?
evapotranspiration, Loss of water from the soil both by evaporation from the soil surface and by transpiration from the leaves of the plants growing on it.
What are four factors affecting evapotranspiration?
What is maximum evapotranspiration?
This ET regimen has been defined as “agronomical maximum evapotranspiration”, ETma, that is the value of ET, often less than ETm, that allows to obtain the optimal technical result among those obtainable, managing only on the water supply.
What is PET and AET?
Traditionally, ET has been studied using four variables: Potential evapotranspiration (PET), Reference Crop Evapotran- spiration, Pan Evaporation, and Actual Evapotranspiration (AET). Of these four variables, AET and PET are the most commonly used in hydrology since they represent two important concepts.