Interpreting SDR results

Hi everyone

I have run the SDR-INVEST model, after building some scenarios in RIOS and I have problems analyzing the results.

1. When I see the results of the table of attributes in shapefile of sub-basins, which according to manual their units are (tons / watershed) for the three scenarios created more in base scenario, I see results in thousands and they seem unrealistic. Are those tons or kilograms? When analyzing the logic of retention and sediment export in the different scenarios, it is logical to increase and decrease according to the scenarios, but the units cause me a lot of doubt (see table in summary sheet, attached with the summarized modeled scenarios)

2. When analyzing the values ​​of sed_export.tif and the sed_export of the resulting sub-basin shape, there are differences, in this case for "sub-basin 2" of 1154. Does the second include some deposition factor because it is higher? See attached table (sheet 2)

3. To compare the results of SDR / INVEST with other data of hydrological models that I have (SWAT), for the same sub-basin, I have doubts as to how to adjust them properly, or if I have to do it with this data (see sheet 2 in attached Excel sheet) )

4. After clarifying the above, I would like to calculate the ROI, since I have replaced my investment portfolio built by RIOS, in one of the modeled scenarios and I used the following formula initially. (see table Summary sheet in columns ROI and its formula)

   Total benefit = (protection export - baseline export) + (protection export - unprotected export)

Are these results logical up to now?

      I will be very grateful with your help


  • swolnyswolny Member, NatCap Staff
    Hello Jainer -

    1. Yes, the units are tons/watershed/year in the shapefile. Have you calibrated the model with observed data? It's hard to know how much different the model is from reality until we compare with observed data. 

    2. Am I understanding correctly that you are comparing the value for subws_id 2 in the shapefile with the value that you get by manually summarizing sed_export.tif within the sub-watershed shapefile? I see that there is a difference in HOJA2/Pregunta 2, and I'm not quite sure how to explain it, except perhaps a bit of a different alignment between shapefile and raster when the model is summarizing versus when you do it manually. @Rich, any other ideas?

    3. When comparing between models, we often look at whether the spatial patterns of high/low values are similar. For which values to compare, each model does have a version of USLE that it uses, and you can compare those for erosion on a particular parcel. If you're more concerned about how much of that erosion makes it to the stream, then I think you should compare the InVEST sed_export with SWAT's SYLD (SYLD is tons/hectare, so you will need to adjust for area.)

    4. It looks like you're using the correct formula for calculating ROI. If the model is not calibrated/validated, then I would use the percent difference between base and the scenarios, not the absolute values.

    ~ Stacie

  • Hello, stacy

    unfortunately I do not have consistent water quality records and sedimentation data to calibrate and my SWAT data were only calibrated for flow. for reasons of time I will leave the calibration pending.

    My results of SDR / INVEST, after running my spatial scenarios (degradation and without protection) with my protection scenarios in which I replaced my investment portfolios with two budgets, ARE negative. I have converted those results to ton / ha / year to facilitate the analysis as shown in the attached table.

    example: row 43, column AE, sub-basin 1, the result is -23.64348615 ton / ha / year
    ?Is that the potential sedimentation reduction product of applying my investment portfolio with respect to the degradation scenario?    see the formula in the attached table HOJA RESUMEN

    Thanks for your support
  • swolnyswolny Member, NatCap Staff
    Hello Jainer -

    Let's look at the equation you're using to calculate column AE, which you've listed above:

    Total benefit = (protection export - baseline export) + (protection export - unprotected export)

    For row 43, (protection export - baseline export) = -1543 tons/year. This shows that the baseline scenario has higher sediment export than the portafolio scenario, so you are getting a benefit from just the portafolio by reducing sediment export by 1543 tons/year.

    and (protection export - unprotected export) = -18698 tons/year. This says that if the areas that are "protected" in your portafolio scenario are unprotected (and degraded) in your degradacion scenario, you would have -18698 tons/year more sediment export in the degradacion scenario. This shows the benefit of protection instead of allowing those areas to degrade. 

    Added together, these give the total benefit due to both the portafolio activities (-1543), and the additional benefit of not letting protected areas degrade (-18698).

    ~ Stacie
  • Very grateful for your answers Stacie, I finally understood how to analyze my SDR results and I am calmer.


    Analyzing my results of NDR-P and NDR-N, in the raster p_export and n_export, It appear with negative values ​​(agricultural use) which is my biggest source as can be seen in the tables of coefficients attached. For urban it is logical but negative agriculture I do not understand.

    Also the values ​​of the table of attributes for sub-basins, specifically the shapefile of phosphorus (sub # 10) which is where horticultural activity is most concentrated and the source of this nutrient also, this appears negative. I have played with the value of "crit_len_p" but it always appears negative.¡.. Any suggestions? .. see attached table please

    In the case of nitrogen, the values ​​of "n_exp_tot" appear in negative except those highlighted in yellow. Any suggestions?

    I have attached the biophysical tables and a summarized Excel sheet +  land use + p_export.tif + n export.tif  to facilitate analysis.

    download the data here please

    Thank you
  • swolnyswolny Member, NatCap Staff
    One thing to remember is that if you do restoration/management activities downslope of agricultural areas, you will see a reduction in export for the agricultural areas. The restored or better-managed areas will retain more nutrient from the agriculture areas, keeping it from making it to the stream. Same for sediment. Does that help explain what you're seeing?

    ~ Stacie

  • Good morning Stacie
    I understand your explanation, but the results that I have attached based on my previous question are from the base scenario, without substituting my investment portfolio for nitrogen and phosphorus. For the case of sedimentation, they already included investment portfolios.

    Any suggestions?
  • swolnyswolny Member, NatCap Staff
    Ah, apologies for not understanding what was happening. I see now that a large area of NDR output actually has pixel values that are negative, which really shouldn't happen. Would you please send the inputs that you're using? I'll run the model and see if I can figure out why.

    ~ Stacie

  • Hello Stacie, 

    I have attached the files and the tables for both nutrient.  I put  pcp and pcp anual as runoff proxy.  I used the anual for my previous run. 

    I appreciatte your help Stacie, I will be expecting you.

    Have a nice Christmas 

    Downlaod the files here

  • swolnyswolny Member, NatCap Staff
    Hello Jainer -

    The model is producing negative values because the biophysical table has eff_n and eff_p values that are greater than one for agriculture. So this is saying that more than 100% of the nutrient can be retained on those pixels. eff_n and eff_p should only have values from 0 to 1, and when I changed those to 1 for agriculture, there were no negative values in the result.

    ~ Stacie

  • Hello Stacie

    Writing about my results, I found a conceptual doubt. To represent the percentage difference of my total benefit in the analysis of return on investment, I made the following operation.

    After applying the formula: Total benefit = (protection export - baseline export) + (protection export - unprotected export) .... to that result per watersheds , I divided it between the sum of total sed_expórt of my base scenario  +  scenario degradation for all watersheds, and then multiplied by 100. (See attached table please, colums  AP-AR, rows 44-65 and 66)

    It confuses me if I should do it under that summation with the base scenario or with the total of my protection scenario, more degradation.
    Or I do not know if the form I'm analyzing is logical and correct?  I will apprecciate tips to analize 

    Thanks you in advance
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