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        I am trying to build biophysical table for water yield model. Coud I ask how to obtain root depth and Kc coefficient. Do I use HWSD ?



  • JamesJames Member
                I am trying to calculate Kc coefficient for biophysical table. I have found rootdepth using monthly global PET rasters (I don't know if OK). I am using Kc calculator for Kc  but I see that land use classes of biophysical table are general (eg. rainfed croplands ). How do I correlate the two ?

    Does anybody know the steps to complete ? I have uploaded the biophysical table and Kc calculator.

  • RichRich Administrator, NatCap Staff
    Hi James, sorry I'm not an expert on this model.  But I do see the user's guide has a Data Sources section that has what looks like some math and data sources for root depth and Kc calculations.

    I hope this is what you were looking for!  Sorry I can't comment on doing it myself though...
  • swolnyswolny Member, NatCap Staff
    Hi James -

    HWSD is for soils, and we usually don't use it for calculating either Kc or root depth. The model does take soil depth (depth to root restricting layer) as an input (which you can get from the HWSD if you don't have more detailed data) and it will use this in its computations, so you don't need to do it separately.

    It looks like you have the FAO data for Kc in your data table - you can use this to calculate Kc. If you have detailed information about the land covers and crop growing seasons, you can use this information, along with Kc(ini), Kc(mid) and Kc(end) to calculate the average annual Kc. If you don't have this kind of detailed information, you can use the Kc(mid) value, understanding that it's likely to overestimate the crop evapotranspiration. 

    For root depth, along with the data sources that Rich linked to, you really need to do a literature search for the vegetation types that are in your area of interest. I'm not sure how you would use PET to calculate root depth, so am curious about your methods there.

    Either way, it's often difficult to find values for the biophysical coefficients that go along exactly with your particular land use/land cover classes, even with an exhaustive literature search. If you cannot find a good match, then you'll need to use the closest that you can find, and note the souce and limitation in your study. 

    ~ Stacie

  • JamesJames Member
            I used the global PET monthly CGIAR CSI dataset (based on WorldClim data): for months in Kc calculator. I counted raster cells and made an average. I noticed the values for rootdepth I am using are wrong.

    The land cover classes (from Globcover) are generic though. I am studying the area of geneva.

    Thank you for your help.


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