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Model Formulation & Parameters / Re: Historic Trend and Histori...
Last post by SAM - April 15, 2020, 05:36:46 AM
Thank you Jonathan for your informative reply.

The time period in my region given by the tide gauge station is from 1948 to 2015.
SLAMM often uses global future SLR estimates and then applies these locally based on the difference between local (RSLR) and global (eustatic) SLR.  [If the future SLR scenarios you are planning to use are localized (RSLR) then set these two parameters to the same value (e.g. 5.2 mm/year each) and move on.]

To estimate future RSLR from global SLR, SLAMM uses the difference between the local trend and the eustatic trend and assumes that that remains consistent into the future. 

However, the eustatic trend value can depend on the time of the measurement.  You want to match the eustatic historic trend time period with the local historic trend time period.

What time period is the 5.2 mm/year based on?

The eustatic rate of SLR is estimated at 1.7 mm/year from 1900 to 2000, but would be greater from 1970-2015 for example.

Here is another time I tried to explain these parameters:

QuoteThe historic trend is assumed to be the [global eustatic SLR] plus or minus [local factors] such as subsidence or uplift or other local meteorological conditions that could cause the difference.  If you are not using a local SLR scenario (running with a eustatic SLR scenario) then those [local factors] are assumed to remain consistent throughout the projection.

Therefore if the local historical trend is 2mm/year greater than the eustatic trend due to subsidence then [local factors] is calculated as 2mm/year and the future SLR is predicted to be 2mm/year greater than eustatic SLR projections.

Historic Eustatic Trend = Global eustatic SLR. (According to technical documentation, use rate of 1.7 mm/yr from 1900 to 2000)

What time period would be best to use for the Historic Trend?

The reason that parameter is there at all is to match the time period of the local historic trend.  Therefore if your local data is from 1970-2000 you would probably want to use a higher historic trend than 1.7 mm/year.

And is it correct that the Historic Eustatic Trend is subtracted from the Historic Trend to identify the isostatic/local trend in SLR?

Yes, that is the whole point of those two parameters.  That is why their time periods should match if possible.

So if you had a local trend of 4 mm/year from 1960-2010 and you have data showing that the historic eustatic trend from 1960-2010 is 2.5 mm/year (rough estimate off the top of my head).  Then SLAMM will assume that the 1.5 mm/year difference is due to local factors and should be added to any eustatic SLR scenarios. 

On the other hand if you have local SLR projections, like many states are producing, then these two parameters should be set to the same value to indicate that you do not want to adjust the future SLR projections as local factors have already been accounted for.  (e.g. using NY specific SLR scenarios, we set both the historic trend and historic eustatic trend to 1.7mm/year.)

Hope this is clear.  -- Jonathan
Model Formulation & Parameters / Historic Trend and Historic Eu...
Last post by SAM - April 10, 2020, 04:56:47 AM
I am using SLAMM 6.7 version. I am confused to give values in Historic Trend (mm/yr) and Historic Eustatic Trend (mm/yr) in edit sites parameters. In my region, the historical rate of sea-level rise is 5.2 mm/yr. What value I will assign in the historical eustatic trend?
Using SLAMM / Re: whether the SLAMM model ca...
Last post by Jonathan S. Clough - April 09, 2020, 07:51:21 PM
That code predates my involvement with the code which started with SLAMM 3 in 1998.  Even if I had it you would need to find some historical compiler to run it on (probably some version of Borland Pascal)

However, the constructs that govern applying the model to large cell sizes remains in the model.  (The capability to model many categories within a single cell.  SLAMM currently holds up to three land types per cell modeled.  However, as cell sizes tend to be small, model initialization is based on a one category-per-cell assumption.)

You would have to be a coder.  It seems to me that the simplest steps would be to:

increase the NUM_CAT_COMPRESS variable which currently only allows 3 classes per cell.

Then the difficulty would be to initialize the model with minimum elevations, widths, and slopes for each category you wish to model in each large cell.

The mapping and GIS linkages wouldn't be particularly useful as they only display the dominant category per cell.

It would take some work in the code -- I'm afraid this type of application is not supported at this time unless someone wants to pay for model development...

Best regards -- Jonathan
Using SLAMM / Re: whether the SLAMM model ca...
Last post by zhiliehui1 - April 03, 2020, 02:15:15 PM
Dear sir

Thank you for your advice?sincerely.

 How can we obtain the early version (mid 1980s) you mentioned? We couldn't find it on the official website.

 Look forward to your reply.
Using SLAMM / Re: Backtrack past conditions?
Last post by Jonathan S. Clough - April 03, 2020, 01:23:29 PM

Backtracking also called "hindcasting" can be done but is often tricky due to lack of high quality elevation data in the past.  Another significant issue is whether enough local SLR has happened since the mid 1990s to have the model predict any significant change in marshes due to the SLR signal (which is the only real perturbation in a SLAMM simulation). 

Please see this thread for some examples and let me know if you have additional questions:

Using SLAMM / Backtrack past conditions?
Last post by jacky - April 01, 2020, 12:29:44 AM
Hello Jonathon and Marco,

I am new to SLAMM. I am wondering whether SLAMM can be used to backtrack past conditions, such as in the 1990s.

Thank you for your wonderful job and help.

Regards! -- Jacky
Using SLAMM / Re: DEM setup
Last post by Jonathan S. Clough - February 07, 2020, 03:18:49 PM
Absent other information you can make the assumption that MSL (the average of continuous measurements or an inferred continuous curve) = MTL (the midpoint between MHHW and MLLW).

Therefore you can leave the MTL-NAVD88 parameter at zero.

Do pay attention to the vertical accuracy of your elevation data as that is an important consideration (is the data set precise enough to model the impacts of incremental changes in SLR?)

Good luck!
Using SLAMM / Re: DEM setup
Last post by azarcos - February 06, 2020, 04:26:35 PM
Thanks Jonathan, I will look to the materials.
The vertical datum is the mean sea level.

Using SLAMM / Re: DEM setup
Last post by Jonathan S. Clough - February 03, 2020, 03:55:41 PM
It has been a while since we have done any in-depth user training or tutorials.  Here is one done in Mexico in 2013.  These materials may be useful to you:


I believe that you are specifying a horizontal datum for your data.  What is the vertical datum of your elevations?  That is what must be converted to a MTL basis in some manner.

Best regards! -- Jonathan
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