Adding Vegetation zones to SNOW-17 - lookup table or vector?

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Lindsey Rotche

• September 15, 2025 17:52

I am trying to add vegetation zones to the SNOW-17 model in goldsim. Currently, zones are based off elevation which you input into a vector. I want to create a secondary zone delimiter based off vegetation that would effect the value of other factors such as melt rates. I have two main questions:

1. I currently have two vectors. One vector has zone numbers and elevation. The other has zone numbers and vegetation assignments. Is this the best way to do it? I would know zone 1 has x elevation from the first vector and y vegetation from the second vector. Or would this make more sense to have them in the same table? I believe vectors can only have one column. So should I do this in a look-up table instead? The lookup tables aren't happy about my column names if I do that because it says they aren't numbers.

2. How to identify which melt factor to use based off the zone's vegetation. I was trying to use a selector for this but GoldSim is not happy about that. Is this the proper tool to be using? Essentially I want an if elif statement that would say:

if vegetation = 10:

melt factor is x

elif vegetation = 20:

melt factory is y

else:

melt factor is z

 

This is my first attempt but I am getting the error "Incompatible data types. The order of the expression result is Scalar, while the input requires Vector[VegZones]." I appologize if the answer is obvious here. I'm still new to goldsim.

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  Lindsey Rotche

  • September 15, 2025 18:34

  I did just realize my issue with the selector is that I had to change the type to scalar, not vector

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  Jason

  • September 16, 2025 17:17

  Lindsey,

  Thanks for writing in our forum. I'm glad you found the issue. But I wonder if there is by chance, a better way than the Selector. Perhaps you could do this using a "vector constructor function". (for more information about vector and matrix constructors, go here: Defining Arrays in an Input Field Using Array Constructor Functions)

  I'm not sure this is exactly what you need but here is a way to get your melt factor from a vegetation table that also is based on elevation: 

  

  ...where Veg_Table is a Data vector:

  Melt_Factor_Table is:

  

  Finally, the Melt_Factor_V expression uses a vector constructor:  

  Note the key here is to use the keyword "row" that references each of the items of the vector, which in this case, correspond to each of the elevation zones. 

  Does that make sense?

  Please let me know if you have any other questions.

  -Jason

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  Lindsey Rotche

  • September 17, 2025 21:16

  Hi Jason,

  This is definitely helpful, but I'm still struggling.

  1. I have used the vector "zones" to create a table for elevation and to create a table for vegetation. Are those now connected in the mind of goldsim?

  2. I believe that vector constructor is doing the following. Please correct me if I'm wrong:

  We once again choose the vector "zones" which should be already connected to elevation and vegetation

  Then it's saying to create a vector based off Melt_Factor_Table, linking that to the veg table:

  

  So does the vector being created look like this?

  Index	Result
  1	0.99
  2	0.85
  3	0.7

  3. I am trying to edit this in the SNOW-17 python code and saw that I had to change that to a vector. This is what I have (Max_Melt_Factor is the same as Melt_Factor_V fyi)

  

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  Jason

  • September 18, 2025 18:43

  Lindsey,

  Yes your result should be as you suspected: [0.99, 0.85, 0.7]. However, in the case you show above, you actually don't need to do that vector constructor because the fact that you are using the "zones" array label set means that the vector of Melt_Factor_Table values is already set up by elevation zone. To your question, "Are those now connected in the mind of goldsim?" the answer is yes. This is because you've assigned each value to each zone in that original data vector. Does that help?

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