[GRASS-user] Global Hydrological modeling with r.watershed, r.stream.extract, r.stream.extract

[Giuseppe Amatulli]

Dear GRASS Team

I am running a global analysis where I need to use "tiles" as computational
units in which I use the following three commands:
r.watershed -b elevation=elv depression=dep accumulation=flow
drainage=dir_rw flow=pixel_area  memory=100000 --o --verbose
r.stream.extract elevation=elv accumulation=flow depression=dep
threshold=0.05 direction=dir_rs stream_raster=stream memory=100000 --o
--verbose
r.stream.basins -l  stream_rast=stream direction=dir_rs   basins=lbasin
 memory=100000 --o --verbose

The basins that were not completely within a tile (resulting in
broken-basins) have been removed (see below the three tiles in Figs. 1,2,3
including only entire basins),
and now I'm in the phase of merging all the tiles having only complete
basins.

When I merge the tiles (Fig 4), some basin borders do not match perfectly,
and some areas have NoData (see Fig 5,6) or have the Basin ID of the below
basin (Fig 7).
I noticed that these phenomena appear only when I merge tiles that have
very large broken-basins that can not be included in the tile due to RAM
limitations.

My thought is that r.stream.basins needs the entire dimension of two
adjacent basins to be able to detect the border without gap and without a
potential random selection.
Is there any part of the r.stream.basins code that I can potentially check
and eventually hack to avoid this problem?

For the rest, all the RAM limitation and other problem have been solved
soon we will have a global stream network and basin delineation performed
100% in GRASS!!!

Thank you
Best Regards
Giuseppe



Fig 1. Left Tile
[image: image.png]


Fig 2. Center tile
[image: image.png]


Fig 3. Right Tile
[image: image.png]


Fig 4. Merge all the tiles
[image: image.png]


Fig 5. Gap -> small white area
[image: image.png]


Fig 6. Gap -> small white area
[image: image.png]

Fig 7. boarder Basins inconsistency among tiles

[image: image.png]

-- 
Giuseppe Amatulli, Ph.D.

Research scientist at
School of Forestry & Environmental Studies
Center for Research Computing
Yale University
New Haven, CT, USA
06511
Teaching: http://spatial-ecology.net
Work:  https://environment.yale.edu/profile/giuseppe-amatulli/
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