Negative Values in n_export for NDR model?

What would cause the NDR model to have negative values? I’m using a 0.1 for subsurface % and length of 50.

For this particular application I’m looking to estimate N export from our upland areas - it’s the coastal areas that have no N load that are showing negative values. Does this mean that they are retaining the upland N?

Sorry, I couldn’t find this question in the database.


Hi @kfalinski,

That is kind of strange. Looking at the equations for export_i, I would think it would always be positive:
export_i = load_i x NDR_i
export_i = load_i x (1-eff'_i) x (1 + exp((IC_i - IC_0) / k))^-1

load_i should always be > 0, (1-eff'_i) should be in the range [0, 1], and exp(x) is always > 0. So I’m not sure where the negative values are coming in. Maybe @jdouglass or @swolny can confirm if this makes sense or not?

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@kfalinski, could you give some examples of the negative values you’re seeing? A common example of this is that pixel values can be numerically close to 0 (within about 1e-5) but negative. If the negative values are outside of that tolerance, there might be a deeper issue here.

Let us know!