[GRASS-user] Ability to model flash flooding

[Thomas Adams]

   Ian,

You may want to look at some U.S. National Weather Service approaches 
with what we call Flash Flood Guidance (FFG):

http://www.weather.gov/oh/hrl/gis/workshop3.html
http://www.weather.gov/oh/rfcdev/docs/ffgitreport.pdf

http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1054&context=usdeptcommercepub&sei-redir=1#search=%22Application%20National%20Geographic%20Information%20System%20Database%22 



Flash Flood prediction is the most problematic in hydrologic forecasting 
because we must make predictions for small uncalibrated catchments and 
at spatial rainfall scales where rainfall estimation can be fairly 
suspect, even with raingauge-corrected radar estimates.

With FFG we try to estimate the amount of rainfall needed within, say, a 
1-hour period, to bring the streams within an individual pixel (maybe, 
1x1 km2 area) to bankfull conditions. Basically, two things are needed:

(1) estimates of the flow (runoff) needed to get to bankfull at each pixel
(2) in an operational setting, since basin conditions change (wetter or 
dryer, for instance) calculating, through a modeling process, the amount 
of rainfall needed to achieve (1) — this is the FFG; so, if that amount 
of rainfall is either observed or is projected to occur, a flash flood 
warning is issued.

Doing (2) is not too difficult; the problem is how to find reasonable 
estimates of (1) and the references I cited describe some methods. There 
is also an approach that tries to identify areas with high POTENTIAL for 
flash flooding 
(http://www.meted.ucar.edu/hazwarnsys/ffewsrg/FF_EWS.App.D.pdf) due to 
physical characterisics: slope, soil type, forest density, percent 
impervious, landuse, etc. The problem is translating the potential for 
flash flooding to flash flood guidance, related to either observed or 
predicted rainfall.

Regards,
Tom


On 8/5/11 9:23 AM, Ian Willis wrote:
> On Fri, 2011-08-05 at 09:32 +0200, peter.loewe at gmx.de wrote:
>> Hello Ian,
>>
>>> To learn how to use grass I've been trying to solve a real world
>>> problem. The problem that I chose was the flash flooding which occurred
>>> in south eastern Queensland. I'd like to see if grass could have
>>> provided reasonably accurate predictions and see if it could be used as
>>> a warning system.
>>> Ideally what I'd like to do is use the archived radar rainfall
>>> information from http://www.bom.gov.au/products/IDR503.loop.shtml#skip
>>> which can be found on http://gw.barratt.com.au/radar/IDR503/2011/01/10/
>>> I am intending extrapolate the rainfall rate using the Z value
>>> conversions recommended for east coast lows as per
>>> http://www.catchment.crc.org.au/pdfs/technical200207.pdf
>>> and then convert the rainfall rate rasters to the resolution of the
>>> aster dem.
>> ...
>>> Any thoughts would be appreciated.
>> some earlier weather-radar related work with GRASS can be found here:
>> http://gisws.media.osaka-cu.ac.jp/grass04/viewpaper.php?id=44
>>
>> http://onlinelibrary.wiley.com/doi/10.1111/j.1467-9671.2004.00178.x/abstract
>>
>> http://opus.bibliothek.uni-wuerzburg.de/frontdoor.php?source_opus=759&la=en [->  the document is in german, but the technical appendices might be of interest for you ->  Z/R realtionship, etc.]
>>
>> FWIW here's study concerning visual quality assessment for 3D radar-met data:
>> http://www.docstoc.com/docs/69767645/4D-data-visualisation-and-quality-control
>>
>> Best,
>> Peter
> Thanks for the info, I failed german when I was 13 but it might be
> interesting to see what a little motivation can do. :-)
>
>
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-- 
Thomas E Adams
National Weather Service
Ohio River Forecast Center
1901 South State Route 134
Wilmington, OH 45177

EMAIL:	thomas.adams at noaa.gov

VOICE:	937-383-0528
FAX:	937-383-0033

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