The output of the NDR module has a large number of null values

Hi, I’ve just tried running the NDR model using InVEST 3.10.2.The model seemed to run successfully,but the n_surface_export and p_surface_export had a large number of nodata value.Further review of the results show that ndr also has a large number of null values, load_n and load_p are complete. And the input data DEM, I have already filled the sink.Log file is attached.Any advice would be really helpful.

Hi @Jerry_Wang , thanks for posting. It doesn’t look like your logfile actually made it through to the post.

It’s also likely we would need to get your input data to get to the bottom of this issue.

Sorry, I did not notice that the log was not uploaded successfully.Now the log is attached,looking forward to your reply
InVEST-Nutrient-Delivery-Ratio-log-2022-12-14–16_48_09.txt (41.6 KB)

Hi @Jerry_Wang -

I don’t see anything obviously wrong in the log file. Have you checked all of your raster inputs to make sure none of them have null values? If any of the raster inputs has null in a pixel, the results will also be null. If you don’t see any problems with the spatial inputs, please send us all of your input data so we can troubleshoot. Thanks.

~ Stacie

I have checked all of my raster inputs, I’m sure none of them have null values. The picture below is the n_surface_export. Besides, I tried to input the official sample data and the result also had null values. The maximum size of upload data is 8MB, I wonder if you can provide me with an email address so I can send you the input data. Thanks!

I see the sample data has nodata values for surface export in the locations of the streams. This is expected since the export value is measuring the amount of nutrient reaching the stream from each pixel, and no in-stream processes are included in this model.

You can see the streams the model is working with in intermediate_outputs/stream.tif. It looks like your DEM might be generating some strange looking streams near the center of your study area, based on the pattern of nodata values in your image. Maybe @swolny has some advice on what to do about that?

Regarding the strange streams near the center of the study area, @Jerry_Wang is that a particularly flat area? Places that are flat (have little to no elevation change over large areas) tend to be difficult for generating streams. With the Multiple Flow Direction algorithm used by NDR, it causes these types of straight, wide streams that are shown in the map. The only thing I can think to try in these places is to “burn” a known correct stream network into the DEM, which is not necessarily an easy thing to do well, and I don’t have much successful experience with it.

Sorry I’m not more useful here, so if anyone else has suggestions, we’d love to hear them!

~ Stacie

The center of the study area is Sichuan basin of China, its internal topography is not very undulating. @swolny Thanks for your answer, and I hope others can give me some useful advice.