[GRASS-user] Repeated r.watershed runs

[Thomas Adams]

Ken,

You wrote:

'If I give r.watershed a precip map as input (flow parameter), doesn't it
route that water down the DEM? And if I know the x,y coordinate of a point
in a stream, doesn't the accumulation at that point represent all of the
up-basin precip that is routed past that point?'

ANSWER: NO!!!! r.watershed is NOT a hydrologic model and does NOT take
precipitation as an input raster.

'Daily water runoff from the Greenland ice sheet for ~50 years'

ANSWER: NO!!!! same as above

You want something like r.topmodel or r.sim.water in GRASS, not that I'm
necessarily suggesting these would meet your needs. There is also ITZI (
https://www.itzi.org/) which may be appropriate since flow over glaciers
(if you're focused on glaciers) in Greenland, should be largely impervious.

You would need r.watershed and r.water.outlet to aid you in the application
of hydrologic models like topmodel, ITZI, and sim.water. But, there are
many dozens more hydrologic models, such as VIC, PRMS, etc.

Tom


On Thu, Aug 31, 2017 at 3:01 PM, Ken Mankoff <mankoff at gmail.com> wrote:

> Hi Tom,
>
> > On 31 Aug 2017, at 20:30, Thomas Adams <tea3rd at gmail.com> wrote:
> > You "want 14,000 values" of what??
>
> One grid cell from each of 14,000 accumulation rasters.
>
> > Your original email stated you were "trying to determine flow past a
> drainage basin outlet" -- r.watershed does NOT do this, if indeed this is
> what you want.
>
> If I give r.watershed a precip map as input (flow parameter), doesn't it
> route that water down the DEM? And if I know the x,y coordinate of a point
> in a stream, doesn't the accumulation at that point represent all of the
> up-basin precip that is routed past that point?
>
> > And you say you have "14,000 flow rasters to be used as input" -- what
> exactly are these 'flow rasters';
>
> Daily water runoff from the Greenland ice sheet for ~50 years.
>
> > what is your goal? I may not understand...
>
> To find the daily stream flow at a point, based on the runoff that feeds
> into that point, or any upstream runoff that eventually makes it to that
> point.
>
> Clearly there is a miscommunication issue here. I apologize if I am not
> being clear or using incorrect terminology.
>
>   -k.




-- 
Thomas E Adams, III
1724 Sage Lane
Blacksburg, VA 24060
tea3rd at gmail.com (personal)
tea at terrapredictions.org (work)

1 (513) 739-9512 (cell)
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