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water yield how to scale from pixel values to watershed values?

Hi guys!
just a very simple question.. how does the program scale up from the pixel value (which is in mm) to the watershed value (in m3)? As far as I understand the mean pixel value is calculated within every basin, as the mean pixel value which is stored in the wyield_mn  column of the shapefile output. After that I supose that this wyield_mn value is multiplied by the number of pixels in the basin but it doesn't give me the answer in the wyield_vol column. Moreover, the units would not balance the equation unless we use the official concept of  mm of water, which stands for 1 liter of water distrituted in un square meter and 1mm of height (this would be a mini cube of water of  1m * 1m * 0.001m = 0.001m3)
Well, let me know how is the approach because we need to scale values of water yield per natural protected areas , so we can not use the values per watershed because several pieces of basin overlap with each protected area!

Thank you!!


  • PerrinePerrine Moderator, NatCap Staff
    Hi Claudia, 

    To convert water yield in mm to a volume in m3, the model multiplies wyield_mn (mean over the watershed) by the watershed area (in m2)  and then divided by 1000 (to convert mm to m).

    Remember that interpreting the water yield outputs at the pixel scale needs to be done with caution since the model was developed to be interpreted at the (sub)watershed scale (although we do use pixel values for some applications, e.g. for pixel-level optimization).

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