I am learning to use the InVEST seasonal water yield model. I am getting negative b_sum values in my output and I’m trying to understand whether this is a problem. In the manual, it says
B_sum_[Suffix].tif (type: raster; units: mm, but should be interpreted as relative values, not absolute): Map of values, the flow through a pixel, contributed by all upslope pixels, that is not evapotranspirated before it reaches the stream
If b_sum represents flow through a pixel, it doesn’t seem to make sense that this would be negative. I’m wondering if this might be caused by some nodata pixels in my hydrologic soil group raster (mainly under water bodies). When I switched out this raster with another version with even more missing data, the minimum value was an even more negative number.
Thanks!
Clicking around the layer in QGIS, it looks like most values are not negative but the automatically calculated range goes down to -20,435 (and up to 71,686,600).
I’m very sorry about the delay in looking into this @KLI and thank you for sharing your model outputs! I’m not yet sure if this behavior is expected and I’ve written to our science team to confirm. As you noticed, B_{sum} is negative in places where we would not expect negative values. In places where B_{sum} is negative, B is 0, which is as we would expect based on the user’s guide description. So I don’t have a concrete answer for you other than to say that I see the problem here and we’re looking into it.
Thanks for your team’s continued work on this. I have been traveling to the field and conferences in the last weeks, so I haven’t had a chance to look into this further. I appreciate the continued updates!