How to calculate evapotranspiration during one season?

How to calculate evapotranspiration during one season?


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  • Kaicun Wang · Beijing Normal University
    I like your method to ask a question. If you want to calculate the evapotranspiration during a season, you have multiple choices. You can find a number of simple methods to do this from the following review paper (It can be downloaded from reseachgate space or directly from webpage of the Journal). Most methods have reasonable auucracy in estimate seasonal evapotranspiration in spite that it is great challenge to estimate its inter-annual or decadal variability.

    Wang, K., and R. E. Dickinson (2012), A review of global terrestrial evapotranspiration: Observation, modeling, climatology, and climatic variability, Rev. Geophys., 50, RG2005, doi:10.1029/2011RG000373.
  • Noha Abdulwarth · Agricultural Research Center, Egypt
    Thanks a lot , i am downloading the paper now
  • Waldo Ojeda · Mexican Institute of Water Technology (IMTA)
    What do you mean for season ET? Many crops with many planting dates? If so, it is more complicated. you need to calculate an integrated ET value based on cropping crop areas.
  • Noha Abdulwarth · Agricultural Research Center, Egypt
    i mean ETo for every crop erea during one season.
    is Penman-Monteith equation suitable FOR that?
  • Kaicun Wang · Beijing Normal University
    Penman-Monteith equation is enough. However, it requires a number of input data. If you don't have these input data, some simplified methods may also works.
  • Waldo Ojeda · Mexican Institute of Water Technology (IMTA)
    I agree. you can use the cropwat software from FAO for those calculations.
  • Noha Abdulwarth · Agricultural Research Center, Egypt
    Thanks a lot
  • Narendra Kumar Gontia · Junagadh Agricultural University
    Noha you may go through following paper
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  • Amartya Saha · Florida International University
    Penman-Monteith is considered as the best estimator for croplands by FAO (Allen et al 2004), provided one has net radiation, windspeed, rel humidity and air temp, as well as crop coefficients, as pointed out by Waldo. If one does not have all the met data, then one can use temp alone (Hamon) or if in a subtropical humid area, net radiation alone (Abtew), or the Turc method. Now, if one is trying to estimate ET for woody vegetation and forests, the problems begin, as it is not possible to accurately measure water uptake by trees (sap flow methods have their own errors), and then water uptake differs vastly by species and phenology. Models attempt to take veg characteristics into account using leaf area index, veg ht etc, but in the end these are just estimates.
  • Noha Abdulwarth · Agricultural Research Center, Egypt
    thanks alot , i am using Penman-Monteith equation now
  • Ngo Phong · Consultative Group on International Agricultural Research
  • Noha Abdulwarth · Agricultural Research Center, Egypt
    Thanks alot already use it :)
    but it's useful answer for any one search for penman - monteith equation and show the question
  • R. Mohebi · University of Kurdistan
    Penman-Monteith ????
  • Noha Abdulwarth · Agricultural Research Center, Egypt
    @R. Mohebi what's wrong??
  • R. Mohebi · University of Kurdistan
    i think that the Penman-Monteith is useful to calculate the evaporate . but i want that software.
  • Bojana Horvat · Independent Researcher
    You may also want to have a look at various methods based on the energy balance approach that integrate information derived from satellite imagery with measured meteorological data at the time of satellite overpass and provide actual daily values. Referent evapotranspiration calculated using FAO Penman Monteith equation is basically an atmospheric water demand as it uses only meteorological data and to relate those values with crop evapotranspiration, crop coefficient must be applied. The approach based on remote sensing takes into consideration not only meteorological data but also surface characteristics (whether it is bare surface or vegetation). Once calculated, daily actual evapotranspiration can be extrapolated to longer time scales (e.g. month, season) through establishing functional relationship with the known parameter(s) that can be assumed to have similar temporal variation as actual evapotranspiration. One of the advantages of such approach is that it enables estimation of spatial variation of ET as well as its quantification. Of course, the care must be taken when it comes to characteristics of the chosen sensor (especially in terms of spatial resolution in comparison with the size of study area).
  • Muhammad Usman · Technische Universität Dresden
    Use FAO ETo calculator for the purpose. You can also download manual of this software for help.
  • R. Mohebi · University of Kurdistan
    Thanks a lot
  • Barry Croke · Australian National University
    Penman-Monteith gives the potential evapotranspiration for a particular vegetation cover (defined from the stomatal and aerodynamic resistances). Generally, this is for a reference crop (clipped grass is typically used), and a crop coefficient used to convert the reference crop estimate to the vegetation cover you are interested in. Converting to actual evapotranspiration (I assume this is what you are really after) requires additional information: soil moisture and a model of how the actual to potential evapotranspiration depends on the soil moisture. If the soil is sufficiently moist throughout the season (e.g. wet seasons in monsoon areas), the actual ET will equal potential ET, but you do need to be careful to check there were not dry spells within the season.

    It is possible to get an estimate of the annual actual evapotranspiration from observations of the rainfall and discharge providing that the soil moisture, groudnwater storage etc are sufficiently similar at the start and end of the year. Going to a seasonal scale, you are not able to use this simple method - you also need information on the differences in the storages from the start to the end of the season.
  • Mahesh Rajendran · Tamil Nadu Agricultural University‎
  • Mohammad Elnesr · King Saud University
    Noha, the question seems unclear!
    What do you mean by "during one season"? and what is the difference between one season, one year, and one month?
    I understood from your answers and profile that you worked with PM method and models, and you are professional in this topic, so what is the problem with you to calculate ET during one season?
    I would like to help you but please clarify your request...
  • HAMIMED Abderrahmane · Mascara Universit
    You mean actual or potential evapotranspiration?
  • Thiago Rodrigues · Universidade Federal de Mato Grosso (UFMT)
    It depends what kind of data do you have...... You can use Penman Monteith if you have meteorological data, and if you have some humidity and temperature gradient you can estimate by Bowen Ratio or Eddy Covariance..... To estimate by Bowen Ratio folow instruction attach
    Temporal Patterns of Energy Balance for a Brazilian Tropical Savanna under Contrasting Seasonal Conditions Thiago Rangel Rodrigues, Sérgio Roberto de Paulo, Jonathan Willian Zangeski Novais, Leone Francisco Amorim Curado, José de Souza Nogueira, Renan Gonçalves de Oliveira, Francisco de Almeida Lobo, George Louis Vourlitis

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