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I would like to sum the values of a grid, moving upstream along flow paths. In other words, I have a grid A with a value for each cell. I need to build a new grid, B, in which the value of each cell should be the sum of the A values of all the cells located downstream along the flow path.

How this can be done in a GIS software (better if QGIS, SAGA or GRASS) or R?

  • what do you mean with flow path? the cell i = 1, j = 1 in grid B is the sum of all the cells in grid A? – Guzmán Dec 5 '16 at 21:29
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r.watershed allows you to specify the "flow" for each cell. So, r.watershed elev=DEM flow=A accumulation=B might work, but it isn't clear from your question if this is what you want. In this scenario, B is the accumulated value of all upstream cells. If this is not what you want, then r.watershed is probably still a good first step, and the output from that can be used with r.stream.channel or other hydrology modules.

See https://grass.osgeo.org/grass73/manuals/r.watershed.html

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