Ken, That would be a gross misapplication of r.watershed and, I'm afraid, is just bad science; I just don't know how to be more clear on that...
Tom On Thu, Aug 31, 2017 at 3:52 PM, Ken Mankoff <[email protected]> wrote: > Hi Tom, > > What if we are assuming instantaneous flow and no storage and all of the > input flow variable leaves the system. Then is r.watershed usable to > calculate accumulation? > > -k. > > Please excuse brevity. Sent from pocket computer with tiny non-haptic > feedback keyboard. > > On 31 Aug 2017, at 21:17, Thomas Adams <[email protected]> wrote: > > 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 <[email protected]> wrote: > >> Hi Tom, >> >> > On 31 Aug 2017, at 20:30, Thomas Adams <[email protected]> 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. > > > >
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