Hargreaves-Samani Evapotranspiration

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    Kim, Homin

    Hello Jason,

    Thanks for your lesson today regarding evaporation which is one of the Water Management webinars series. I just wanted to follow up with you on Daily extraterrestrial radiation ('RadEx' element in model) especially when Latitude is greater than 67 degree (I was not a questioner). Such so, arccos(x) in Omega element could not be calculated when Lat is greater than 67 degree because of the limitation of x range which is between -1 and +1. In order to get daily extraterrestrial radiation where Lat is greater than 67 degree, I prefer to use the 15th day of the month value instead of using 'DayofYear' in 'Delta' element and GoldSim could interpolate/estimate daily 'RadEx'.

    Here is the reference table and see Table 2.6 and there are some comments above and below the table regarding Ra. For example, 'For the winter months in latitudes greater than 55° (N or S), the equations for Ra have limited validity. Reference should be made to the Smithsonian Tables to assess possible deviations'

    http://www.fao.org/3/X0490E/x0490e0j.htm#annex%202.%20meteorological%20tables

    As well as it could be implemented in 'Reference ET model' or other models. I think it's only for very high latitude situations and just wanted to let you know my thoughts. 

    Thanks in advance for your taking your time to consider this.

    Regards,

    Homin Kim

     

     

     

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    Jason

    Model update:

    This model was updated with more thorough documentation and verification testing.

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