GRIB-API definition
Name | percolation | Abbreviation | perc | Unit | kg m-2 | paramId: | 260430 |
UERRA details
Definition | The percolation is the downward movement of water under hydrostatic pressure in the saturated zone. This water might still end up in rivers and lakes as discharge but it is a slower process than water runoff or drainage. Such defined percolation is an input for hydrological models together with e.g. water runoff. |
Validity | accumulated (from the beginning of the forecast) |
Comment |
WMO GRIB2 definition
Parameter | ||
---|---|---|
Discipline | 1 | hydrological products |
Parameter category | 0 | hydrology basic products |
Parameter number | 16 | percolation rate** |
Type of statistical processing | 1 | accumulated |
**newly approved by WMO (release in May 2016)
Level | ||
---|---|---|
Type of first fixed surface | 177 | Deep soil (of indefinite depth) |
Scale factor of first fixed surface | all bits to 1 | missing |
Scaled value of first fixed surface | all bits to 1 | missing |
Type of second fixed surface | all bits to 1 | missing |
Scale factor of second fixed surface | all bits to 1 | missing |
Scaled value of second fixed surface | all bits to 1 | missing |
9 Comments
Richard Mladek
@Sebastien Villaume
Sent: Wednesday, 24 June, 2015 1:31:21 PM
Subject: Re: urgent quick help - some MF surface parameters
> drainage (separate from runoff which is another used parameter..)
well, WMO has only one parameter for both drainage and run off, Discipline 2 Product Category 0 - Parameter 33. My guess is that the same parameter should be use but on 2 different types of Level, like above or below surface or something. I am not an expert but I thought that runoff occurs above the surface and drainage is water taken from under surface? Or?
Richard Mladek
There is a special level 106 "Depth below land surface" in GRIB2 but how to specify the bottom level for drainage?
Or maybe there is some special type of subsurface layer defined which I missed but could be used?
Fredrik Wetterhall
There are in total 6 different runoff definitions by WMO (some hydrological) which is quite excessive. The definition of runoff is water that leaves the the soil/ground and becomes surface water.
If we stick to the land surface (Disc 2, cat 0), Number 5 is Water runoff, so that should be used for normal runoff. Parameter 33 could be used for the drainage I assume, since you have used Param 34 for Surface water runoff. We can have a chat about this tomorrow morning.
Per Unden
Richard Mladek
Eric Bazile (Sent: Thursday, 15 October, 2015 2:36:35 PM)
Runoff is the water going out the surface reservoir (after precipitation) : lateral path (water is lost for the model). Drainage is the water at the bottom of the deepest layer : vertical. Both are used as input for hydrological model. For runoff and drainage: accumulated Kg/m2 for one hour. I think, in general, for fields available hourly, the accumulated period will be 1 hour.
Fredrik Wetterhall
Ok, so drainage in this sense is what in hydrology is called percolation. This water is still interacting with the water that ends up in rivers and lakes as discharge, but it is a slower process.
Richard Mladek
If percolation is really what MF produces and should go into UERRA archive we should propose that as a new parameter to WMO as the currently existing WMO "Water runoff and drainage" does not seem to be the same thing.
Per Unden
Richard Mladek
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