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I calculated Topographic Wetness Index (TWI) using SAGA and TauDEM. Overall trend is similar but SAGA returned larger values compared with TauDEM. Sometimes the deviations are as large as 7 or 8. I am using 1 m resolution DEM. I suppose the calculation methods are the same.

What is causing these differences?

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    What's your basis for supposing the calculation methods are the same? Did you read the technical documentation for each of those tools? The Wikipedia article about TWI says "Methods of computing this index differ primarily in the way the upslope contributing area is calculated," so presumably there are different ways of computing it. – csk Oct 21 at 19:26
  • You are, in fact, incorrect. The methods are different. It is up to you to figure out how and in understanding why it may matter. – Jeffrey Evans Oct 22 at 1:45
  • Hi, Thank you for your replies. I originally looked at the algorithm reference papers both applications were listing. But when I was looking at the results today, I realized that probably the catchment calculations were different or some part of either calculation was inverted. I’ll look into them. Thanks! – Sumi Oct 23 at 0:15

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