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Other equations for estimating evapotranspiration from meteorological data include the Makkink equation, which is simple but must be calibrated to a specific location, and the Hargreaves equations. To convert the reference evapotranspiration to the actual crop evapotranspiration, a crop coefficient and a stress coefficient must be used.
It uses meteorological data from the moment of the recording of the satellite data to solve the 'instantaneous' energy balance, and uses extrapolation to calculate daily evapotranspiration. Using a time series of satellite and meteorological data, periodic cumulative (e.g. weekly, monthly, yearly) evapotranspiration data can be calculated.
Crop coefficients are properties of plants used in predicting evapotranspiration (ET). The most basic crop coefficient, K c, is simply the ratio of ET observed for the crop studied over that observed for the well calibrated reference crop under the same conditions.
The coefficients 0.408 and 900 are not unitless but account for the conversion from energy values to equivalent water depths: radiation [mm day −1] = 0.408 radiation [MJ m −2 day −1]. This reference evapotranspiration ET 0 can then be used to evaluate the evapotranspiration rate ET from unstressed plants through crop coefficients K c: ET ...
Evapotranspiration is a measure of all of the water that evaporates from land surfaces plus the water that transpires from plant surfaces. [2] Based on the amount of water that does evaporate and transpire, the user can water crops correspondingly, which results in less water use and possibly increased crop yields.
In 1948, C. W. Thornthwaite proposed an AI defined as: = where the water deficiency is calculated as the sum of the monthly differences between precipitation and potential evapotranspiration for those months when the normal precipitation is less than the normal evapotranspiration; and where stands for the sum of monthly values of potential evapotranspiration for the deficient months (after ...
Inputs to SPEI datasets can include high-resolution potential evapotranspiration (PET) from the Global Land Evaporation Amsterdam Model (GLEAM) and hourly Potential Evapotranspiration (hPET). GLEAM is a set of algorithms designed to calculate actual evaporation, PET, evaporative stress, and root-zone soil moisture.
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. Simpler Hydrometeorological equations continue to be used where obtaining such data is impractical, to give comparable results within specific contexts, e.g. humid vs ...