How do you calculate evapotranspiration?
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 2. This will give you a good estimate for the average temperature during that time.
What is the Thornthwaite equation?
The Thornthwaite (1948) equation is a widely used empirical method for estimating potential evapotranspiration (PET). The equation only requires mean monthly air temperature and mean daily daylight hours for each month, which can be calculated from latitude.
How do you calculate monthly evapotranspiration rate?
- Rs = (0,25 + 0,5*n/N)*Ra.
- Rs = kRs*(Tmax – Tmin)^0.5*Ra.
- ETo = 0.0023*0.408*Ra*(Tavg+17.8)*(Tmax – Tmin)^0.5.
- ETo = 0.0025*0.408*Ra*(Tavg+16.8)*(Tmax – Tmin)^0.5.
- ETo = 0.0023*0.408*Ra*(Tavg+17.8)*(Tmax – Tmin)^0.424.
- ETo = 0.0020*0.408*Ra*(Tavg+33.9)*(Tmax – Tmin)^0.296.
How do you calculate evapotranspiration in a watershed?
Obviousely, you want to estimate ET (evapotranspiration) using the water balance method: ET=P-R-TWSC, where P is precipitation, R is runoff and TWSC is change in terrestrial water change.
What is ETo in irrigation?
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 evapotranspiration rate?
The evapotranspiration rate is normally expressed in millimetres (mm) per unit time. The rate expresses the amount of water lost from a cropped surface in units of water depth.
How do you calculate aridity?
Aridity Index (AI) is a numerical indicator which is used for measuring the degree of dryness of climate of a place. It is opposite to humidity index. It is calculated as the ratio of P/PET, where P is the average annual precipitation and PET is the potential evapotranspiration (UNEP, 1992).
What is Thornthwaite moisture index?
Abstract. The Thornthwaite moisture index is a useful indicator of the supply of water (precipitation) in an area relative to the demand for water under prevailing climatic conditions (potential evapotranspiration).
How do you calculate an AET for a pet?
If you do not have all these data, use a simpler formula: ET= 19.86+0.77*PET-0.04*P. Where PET is Potential ET using Hamon’s method, P= monthly total rainfall. As you can see, for tropical forests, PET is the best predictor.
How do you calculate watershed?
The formula for the area of a square is length x length. So, the area of each square = 500 x 500 feet, or 250,000 feet. square, this will give you the total size of the watershed area.
How do you calculate ETo?
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.