Why is this happening
Hello @Beipoerdawang -
The empty values are probably located within streams. To verify this, compare it with the streams.tif output layer. For more information, please search this forum, this topic has been discussed many times.
~ Stacie
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It’s true that it’s water, it’s relatively flat, but is there any good solution to keep it from being empty?
Since the NDR model doesn’t include any of the complex processes that happen in streams, the model only provides results for the pixels of the landscape that drain into streams, not the stream pixels themselves. So anywhere there are streams, there will be NoData values.
It does make things more difficult that the Multiple Flow Direction (MFA) algorithm that InVEST uses often creates streams that are very wide. This is especially true in very flat terrain (which is always hard to model streams for), and from your map I’m guessing that the large red part of the study area is flat.
The only thing I’m aware of that you could try is to pre-process your DEM to “burn in” narrow streams, so hopefully the model will generate a stream network that is much thinner, and there will be less NoData. But still, there will always be NoData where there are streams.
~ Stacie