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#11
Using SLAMM / Re: Model calibration
Last post by Jonathan S. Clough - June 16, 2020, 06:22:33 AM
The time-zero run is a very important step.  To the extent possible, it should not be any different than the model's initial conditions.  It tests that the conceptual model, the wetland coverage, the elevation data, and the tide range data are all consistent.  In the results the initial condition is shown as "0" and the "time zero" result is shown as the first date of the simulation.

From the tech doc:
SLAMM can also simulate a "time zero" step, in which the conceptual model can be validated against the data inputs for your site. The time-zero model predicts the changes in the landscape given specified model tide ranges, elevation data, and land-cover data. Any discrepancy in time-zero results can provide a partial sense of the uncertainty of the model. There will almost always be some minor changes predicted at time zero due to horizontal off-sets between the land-cover and elevation data-sets, general data uncertainty, or other local conditions that make a portion of your site not conform perfectly to the conceptual model. However, large discrepancies could reflect an error in model parameterization with regards to tide ranges or dike locations, for example, and should be closely investigated.

I would suggest setting up the model to run for a couple of years (photo date, photo date + 1, photo date + 1) with minimal or zero SLR.  Any changes predicted should be understood as much as possible in terms of data error (issues with the tide model, DEM, or wetland coverage), lack of dike or seawall accounting, etc.  You should also examine the inundation frequency maps to ensure that the wetlands are being regularly wetted.  You can consider using the results from the time-zero run as your initial condition for your projection runs to ensure that the effects that you are seeing in the simulation are from the SLR signal and not uncertainty or lack of precision in your input data sets.

Sorry about the long delay in response.  -- Jonathan
#12
Using SLAMM / Model calibration
Last post by azarcos - June 02, 2020, 04:27:05 AM
Hi Jonathon,

I am new to SLAMM. I want to conducted model calibration by running the "time zero" step, following the same methodology in Clough et al. (2016). I know already that no sea-level rise, accretion or erosion should be considered, but I am not sure about what to introduce in the last year of simulation. For how long should I run the model?
In the SLR scenarios to run' should I apply 0m by 2100? Can you please provide more details on the calibration procedure?
Thanks for your help

cheers
Rita
#13
Using SLAMM / Re: Run the model using Classi...
Last post by Jonathan S. Clough - April 27, 2020, 07:22:05 AM
Yes, it's the first question you are asked when creating a new SLAMM simulation.

"Use California Categories?"  Answer "no" to use "classic" SLAMM categories.

#14
Using SLAMM / Run the model using Classic SL...
Last post by SAM - April 25, 2020, 08:22:01 PM
Dear Jonathan,

Is it possible to run the model in SLAMM 6.7 using classic SLAMM categories?
#15
Here are some references:

Start Date End Date Rate Source N
1900 2000 1.7 mm/year +-0.5 IPCC 2007a §5.5.2.1 http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch5s5-5-2.html
1961 2003 1.8 mm/year +- 0.5 IPCC 2007a §5.5.2.1 http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch5s5-5-2.html
1993 2003 3.1 mm/year Grinsted et al. (2009).  Historical Data
1993 2003 3.3 mm/year Grinsted et al. (2009).  Satelite Altimetry

Also see http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch5s5-5-2-5.html

So maybe assume 1.8 mm/year from 1948-2003 and then 3.3 mm/year from 2003-2015?  So something like 2.1 mm/year for 1948-2015 perhaps?

There may be some newer references-- I haven't done a literature search recently.
#16
Model Formulation & Parameters / Re: Historic Trend and Histori...
Last post by SAM - April 14, 2020, 11:36:46 PM
Thank you Jonathan for your informative reply.

The time period in my region given by the tide gauge station is from 1948 to 2015.
#17
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
#18
Model Formulation & Parameters / Historic Trend and Historic Eu...
Last post by SAM - April 09, 2020, 10:56:47 PM
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?
#19
Using SLAMM / Re: whether the SLAMM model ca...
Last post by Jonathan S. Clough - April 09, 2020, 01:51:21 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
#20
Using SLAMM / Re: whether the SLAMM model ca...
Last post by zhiliehui1 - April 03, 2020, 08:15:15 AM
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.