[GRASS-user] faster watershed routing

[Ken Mankoff]

It seems the easiest way to speed this up is to parallelize it, which can
be done fairly easily with GNU parallel.
https://grasswiki.osgeo.org/wiki/Parallelizing_Scripts#GNU_Parallel

On Sat, Feb 11, 2017 at 8:12 AM, Ken Mankoff <mankoff at gmail.com> wrote:

> Hi GRASS list,
>
> I have a watershed raster with 200 million cells. I calculate the basins
> and the baseline accumulation (i.e. flow=1) and have done so with
> r.watershed like this:
>
> r.watershed -a elevation=e drainage=d accumulation=a basins=b
> threshold=50000 --q
>
> That takes ~2 minutes.
>
> I now need to calculate surface flow ~1000 times over this same watershed
> (every day for 3 years). That would take 1.5 days which is not
> unreasonable. But is there a faster way? Can I use the pre-computed basins
> and accumulation rasters? Is it faster to loop over the basins (there are
> ~1000 of them)? Or do I just run the entire command as above 1000 times but
> with variables for flow= and accumulation=?
>
> Thanks,
>
>   -k.
>
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