What is FAO Penman Monteith equation?

The FAO Penman-Monteith equation determines the evapotranspiration from the hypothetical grass reference surface and provides a standard to which evapotranspiration in different periods of the year or in other regions can be compared and to which the evapotranspiration from other crops can be related.

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 determined by the aerodynamic resistance in Penman Monteith equation?

The surface resistance, rs, describes the resistance of vapour flow through stomata openings, total leaf area and soil surface. The aerodynamic resistance, ra, describes the resistance from the vegetation upward and involves friction from air flowing over vegetative surfaces.

What is the Hargreaves equation?

The Hargreaves equation (Hargreaves and Samani, 1985) is a simple evapotranspiration model that only requires a few easily accessible parameters: mininimum, maximum and mean temperature, and extraterrestrial radiation.

What is modified Penman method?

Penman’s combination mass transfer and energy balance method for estimating evapotranspiration has been modified for application to a forest environment. Hence, the potential evapotranspiration (PEf) is a good estimation of the actual evapotranspiration (AEf) in this area.

What is Thornthwaite method?

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.

What is Penman Monteith model?

Like the Penman equation, the Penman–Monteith equation (after Howard Penman and John Monteith) approximates net evapotranspiration (ET), requiring as input daily mean temperature, wind speed, relative humidity and solar radiation.

How do you calculate aerodynamic resistance?

The drag equation states that drag D is equal to the drag coefficient Cd times the density r times half of the velocity V squared times the reference area A. For given air conditions, shape, and inclination of the object, we must determine a value for Cd to determine drag.

What is Blaney Criddle method?

Usage. The Blaney–Criddle equation is a relatively simplistic method for calculating evapotranspiration. The equation calculates evapotranspiration for a ‘reference crop’, which is taken as actively growing green grass of 8–15 cm height.

How do you calculate potential evapotranspiration?

the FAO+56 IS THE BEST AND ACCURATE FORMULA FOR CALCULATING THE ET0. Potential evapotranspiration (ETP), expressed as the evaporated water slice, is the sum of the amounts of water that can evaporate and transpire on a given surface and for a well-defined period of time, considering inputs from sufficient water.

What is ET equation?

The ET is calculated for a grass reference crop using a modified Penman Monteith equation, which is the standard method recommended by the UN Food and Agriculture Organization. Calculated evapotranspiration depends on a number of factors including temperature, solar radiation, vapour pressure, and wind speed.

Who proposed modified Penman method?

The Penman equation describes evaporation (E) from an open water surface, and was developed by Howard Penman in 1948. Penman’s equation requires daily mean temperature, wind speed, air pressure, and solar radiation to predict E.

What is the Penman Monteith equation?

Penman-Monteith equation In 1948, Penman combined the energy balance with the mass transfer method and derived an equation to compute the evaporation from an open water surface from standard climatological records of sunshine, temperature, humidity and wind speed.

What is the FAO Penman-Monteith equation?

FAO Penman-Monteith equation This chapter introduces the user to the need to standardize one method to compute reference evapotranspiration (ETo) from meteorological data. The FAO Penman-Monteith method is recommended as the sole ETomethod for determining reference evapotranspiration.

How accurate is the modified Penman equation?

The modified Penman was frequently found to overestimate ETo, even by up to 20% for low evaporative conditions. The other FAO recommended equations showed variable adherence to the reference crop evapotranspiration standard of grass.

What is the ASCE Standard for evapotranspiration?

ASCE Standardized Reference Evapotranspiration Equation(s) Both standardized reference equations were derived from the ASCE-PM by fixing h = 0.12 m for short crop (ETo) and h = 0.50 m for tall crop (ETr).