Depth to Bedrock ?

[gnikulin]

In CORDEX we have a request for a variable which we call Depth to Bedrock (lower boundary of land surface models). In the CF Standard Name Table I only found bedrock_altitude (also discussions here https://github.com/cf-convention/vocabularies/issues/8). Should we request a new standard name (e.g. bedrock_depth) or may be there is something similar that can be used ?

[JonathanGregory]

Dear Grigory @gnikulin

Thanks for the question. Following the usual meanings in standard names, bedrock_depth would mean the vertical distance of the top of the bedrock below the solid surface (the bottom of the atmosphere). Is that what you mean by it? An alternative, which might mean the same thing in practice and might be clearer, would be to call it soil_thickness. What do you (and others) think?

Cheers

Jonathan

[gnikulin]

Thanks Jonathan !!!!

Yes, a better alternative to bedrock_depth is indeed something like soil_thickness (e.g. the thickness of the permeable soil layer above bedrock). I see that soil depth is also used sometimes with the same meaning (e.g. the distance from the soil surface to the underlying bedrock). I'll check with experts whether soil_thickness fits or not.

[JonathanGregory]

Thanks, Grigory. In CF standard names, we use the word thickness for the vertical extent of a layer. As you say, the word "depth" is sometimes used to mean "thickness", but in CF standard names depth means the vertical distance below the Earth's surface (solid or sea level, bottom of the atmosphere).

[gnikulin]

It took a bit of time to discuss this issue with several groups working with land surface models. It was noted that in a geological sensesoil_thickness is not always equal to depth_to_bedrock. Soil is the product of pedogenesis, but between soil and bedrock, much sediment, mineral material might be deposited still. Fore example this dataset provides "the thickness of the permeable layers above bedrock (soil, regolith, and sedimentary deposits)" Of course, it depends on the definition of soil and in climate modelling, I think, we always assume that the soil layer is a permeable layer between the surface and bedrock. Perhaps depth_to_bedrock helps to avoid any ambiguity ?

[taylor13]

I think depth_to_bedrock would be correctly interpreted by most folks, but bedrock_depth might be misinterpreted by some as the thickness of bedrock. (But I could be wrong about that.)

[JonathanGregory]

I suggest bedrock_depth_below_ground_level, on the pattern of the existing name sea_floor_depth_below_sea_surface. Would that be clear?

[taylor13]

that's even clearer to me. Grisha (@gnikulin), what do you think?

[gnikulin]

bedrock_depth_below_ground_level is indeed clear enough and sounds fine for me

[efisher008]

Dear Grigory @gnikulin,

As it looks like the format of the prospective standard name has been agreed, would you now like to make the official proposal for the name? This should include the standard name, units, description, and proposer name and date. This can be done in this issue or you can open a new one if you'd prefer.

Best regards, Ellie

[gnikulin]

Thanks Ellie !!! I can propose the name in this issue.

New standard name: bedrock_depth_below_ground_level Units: m Description: The bedrock_depth_below_ground_level is the vertical distance between the ground and the bedrock Proposer name: Grigory Nikulin Date: 2024-04-03

I'm not sure if the proposed description is enough or we need more details ?

Best regards,

Grisha.

[taylor13]

Some may think otherwise, but I think the description is sufficient (once a period is added to the end of the sentence).

[efisher008]

Thank you @gnikulin, I have added the name to the editor. There was a typo in the date; the year was changed to 2024, and I've updated your message with this.

[github-actions[bot]]

Thank you for your proposal. These terms will be added to the cfeditor (http://cfeditor.ceda.ac.uk/proposals/1) shortly. Your proposal will then be reviewed and commented on by the community and Standard Names moderator.

[efisher008]

Hi @gnikulin,

I've been looking at the CF phrasebank and think it might also be useful to include the definitions for "bedrock" and "ground_level" after your proposed text. These are below:

• "Bedrock" is the solid Earth surface beneath land ice or ocean water.
• _"groundlevel" means the land surface (including beneath snow, ice and surface water, if any).

What do you think of this?

Best wishes, Ellie

[taylor13]

If we include these definitions, then:

I think "bedrock" more generally refers to the solid rock that is typically buried beneath soil and other broken or unconsolidated material. In our usage above, of course it may lie under land ice or ocean water too.

I think our description of "ground_level" should specify whether surface vegetation is assumed to be above or below the "ground_level". On the other hand, we may want to leave that point vague.

Perhaps "Earth surface" refers to the top of the ground itself or, if present, the top of the uppermost solid substance lying on the ground, be it water, vegetation, snow, ice, or man-made structures. The "ground_level" could then be the surface below any/all of these??? Not sure.

[JonathanGregory]

In existing standard names, "ground level" is used to indicate the interface between snow and soil. I think therefore it is beneath the above-ground vegetation, but the roots are below ground level! J

[gnikulin]

I see that "Bedrock" is the solid Earth surface beneath land ice, ocean water or soil. is included in description of 3 standard names where bedrock appears - bedrock_altitude, bedrock_altitude_change_due_to_isostatic_adjustment and tendency_of_bedrock_altitude. Seems "or soil" was simply missing. Using the same definition "Bedrock" is the solid Earth surface beneath land ice, ocean water or soil. sound fine for me since in our case we assume where land.

Regarding "_groundlevel" I'm not sure that we need to mention vegetation here, I didn't get this point. The definition of ground_levelthat appears in several standard names:

• _"groundlevel" means the land surface (including beneath snow, ice and surface water, if any) in upward_geothermal_heat_flux_at_ground_level_in_land_ice
• _groundlevel means the land surface (beneath the snow and surface water, if any) in upward_heat_flux_at_ground_level_in_snow
• _groundlevel means the land surface (beneath the snow and surface water, if any) in upward_heat_flux_at_ground_level_in_soil

_groundlevel" means the land surface (beneath snow, ice and surface water, if any) sounds better for me

[gnikulin]

Although "Bedrock" is the solid Earth surface beneath land ice, ocean water or soil. says nothing about surface fresh water, lakes etc.

[taylor13]

The existing definition of "bedrock" quoted above could be amended to read: "Bedrock" is the solid Earth surface beneath any land ice, surface waters (including ocean), soil, and other broken or unconsolidated surface material.

Regarding ground level, I note that for upward_geothermal_heat_flux_at_ground_level_in_land_ice the description states this "is the upward heat flux at the interface between the ice and bedrock". Is this correct? Doesn't scree-like material often underlie a glacier? If so, shouldn't this say "heat flux at the interface between the ice and underlying ground"?

For other standard names that reference "ground_level", I think most folks with interpret this as did @JonathanGregory: "it is beneath the above-ground vegetation, but the roots are below ground level". If this is so, then there probably is no need to revise the description.

[JonathanGregory]

We could define ground_level as the level of the solid land surface (beneath any snow, land ice, surface water and permanent inland water). That means the bed or a lake or river would be "ground". Does that make sense? ground_level is not defined in sea areas. On Karl's point, I think that for upward_geothermal_heat_flux_at_ground_level_in_land_ice we could say "at the interface between the ice and the underlying sediment or bedrock."

I agree that bedrock is the solid Earth surface beneath any land ice, surface waters (including ocean), soil, loose rock, and unconsolidated sediment. Is it helpful to say "beneath the regolith"? Does bedrock include consolidated sediment i.e. sedimentary rock?

[gnikulin]

bedrock exists everywhere beneath any surface. May be regolith is a right word to describe "soil, and other broken or unconsolidated surface material" suggested by Karl. Britannica defines the regolith as "a region of loose unconsolidated rock and dust that sits atop a layer of bedrock. On Earth, regolith also includes soil, which is a biologically active medium and a key component in growth." something like that - "Bedrock" is the solid Earth surface beneath any land ice, surface waters (including ocean) and regolith.

[gnikulin]

We could define ground_level as the level of the solid land surface (beneath any snow, land ice, surface water and permanent inland water). That means the bed or a lake or river would be "ground". Does that make sense? ground_level is not defined in sea areas. On Karl's point, I think that for upward_geothermal_heat_flux_at_ground_level_in_land_ice we could say "at the interface between the ice and the underlying sediment or bedrock."

In our application (land surface modeling) ground_level can be defined only over land. I wouldn't call lake or river bed ground_level, although it has been already defined for heat fluxes.

[JonathanGregory]

Thanks for the definition of "regolith", Grisha. Maybe it's easier if we use words from that definition, so that people don't have to look up "regolith" for themselves. Sorry for the digression. In the existing standard names, and your new one, "bedrock" is used as a level. How about In this standard name, "bedrock" refers to the surface of the consolidated rock, beneath any unconsolidated rock, sediment, soil, water or land ice.

I agree that ground_level does not obviously refer to the bed of a lake or river. Let's postpone that discussion until it's needed. For the moment, we could define ground_level as The level of the solid surface in land areas without permanent inland water, beneath any snow, ice or surface water. What do you think?

[gnikulin]

I agree that meaning of the regolith can be simply unknown to many of even most users of the CF conventions. I didn't know what it actually means until yesterday :-). I think that "bedrock" refers to the surface of the consolidated rock, beneath any unconsolidated rock, sediment, soil, water or land ice is clear enough.

The level of the solid surface in land areas without permanent inland water, beneath any snow, ice or surface water. should work as well.

[efisher008]

Hi all,

I've just finished following the discussion of bedrock and ground_level through your comments. I have updated the text for the proposed name bedrock_depth_below_ground_level to the following: _"The bedrock_depth_below_groundlevel is the vertical distance between the ground and the bedrock. "Bedrock" refers to the surface of the consolidated rock, beneath any unconsolidated rock, sediment, soil, water or land ice. "Ground level" means the level of the solid surface in land areas without permanent inland water, beneath any snow, ice or surface water."

Are you proposing to change the definition of bedrock and ground_level in the CF phrasebank to these new sentences, or just in the description for the new proposed name? I think it should be a consistent usage between what's in the term description and the phrasebank so it would be good to have a conclusion either way. I would also suggest we could create a phrasebank entry for regolith: "soil, and other broken or unconsolidated surface material". What are your thoughts on this?

Best regards, Ellie

[JonathanGregory]

Dear Ellie

I believe our new definitions of bedrock and ground_level are fine for the existing standard names containing these phrases viz.

bedrock_altitude bedrock_altitude_change_due_to_isostatic_adjustment tendency_of_bedrock_altitude downward_heat_flux_at_ground_level_in_snow downward_heat_flux_at_ground_level_in_soil ground_level_altitude upward_geothermal_heat_flux_at_ground_level_in_land_ice upward_heat_flux_at_ground_level_in_snow upward_heat_flux_at_ground_level_in_soil.

Therefore we can amend them in the phrasebank.

We could define regolith but we aren't using that word at the moment, are we? Do we have other phrases defined that aren't used in standard names?

Best wishes

Jonathan

[efisher008]

Hi Jonathan,

I have changed the definitions of the terms bedrock and ground_level in the phrasebank to our agreed text (as seen in the name description here). I think it could still be useful to define regolith following this discussion, in the event that it is (presumably) required in a name in future, and the above discussion does not need to be repeated (possibly yielding a different outcome).

We could define regolith but we aren't using that word at the moment, are we? Do we have other phrases defined that aren't used in standard names?

I think the answer to this is "possibly not", however there would be no quick way to check the whole phrasebank against the current standard names table for unused phrases. This could be a useful exercise in the future though.

I am not familiar with the standard approach to this in CF, is it usually the case that phrases are/should only be added when they are actively used in a standard name?

Best wishes, Ellie

[JonathanGregory]

Dear Ellie

Thanks for you attention to this. You ask

I am not familiar with the standard approach to this in CF, is it usually the case that phrases are/should only be added when they are actively used in a standard name?

I don't recall this being explicitly discussed (Alison @japamment or Fran @feggleton might comment) but I would expect that we have only included phrases in the phrasebank that are actually in use, because that would accord with the usual CF practice (number 2 of the CF principles) that we don't add things unless there's a definite use-case).

Best wishes

Jonathan

[efisher008]

Dear Jonathan,

Thank you for your reply and for linking to the principles. That was what I was hoping to find out and I agree it would be in keeping with principle 2 that we do not add regolith into the phrasebank for now. If we need to revisit that in the future in light of a potential use-case, we would at least have a starting definition to work from.

Best wishes, Ellie

[efisher008]

Dear Grigory @gnikulin,

Your proposed name bedrock_depth_below_ground_level has now been accepted in the CF editor. This will be published in the next update to the standard names table (v85), which is scheduled for mid-May 2024. Thank you very much for your proposal!

Best wishes, Ellie

[JonathanGregory]

Yes, I agree, Ellie. J

[gnikulin]

Many thanks to all who helped with the new standard name !!!!

[efisher008]

Closing this issue as this name has been accepted in version 85 of the CF standard names table, published on 21 May 2024 (https://cfconventions.org/Data/cf-standard-names/85/build/cf-standard-name-table.html).