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https://github.com/munterfi/glacier-flow-model

Modeling glaciers on a digital elevation model (DEM) based on mass balance and a modified D8 flow algorithm applied to ice.
https://github.com/munterfi/glacier-flow-model

digital-elevation-model geographical-information-system geospatial glacier glaciers-flow gradient mass-balance modeling

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Modeling glaciers on a digital elevation model (DEM) based on mass balance and a modified D8 flow algorithm applied to ice.

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README 

        
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==================

Glacier flow model

==================



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Modeling glaciers on a digital elevation model (DEM) based on mass balance and

a modified D8 flow algorithm applied to ice.



The modeling is based on a linear relationship between altitude and mass

balance, the so-called mass balance gradient. For alpine glaciers this gradient

is about 0.006 m/m. Continental glaciers tend to be at 0.003 and maritime

glaciers at 0.01 m/m. The alpine gradient is set by default in the model.

To model the glaciers, annual steps are calculated. First the mass balance

(accumulation and ablation) for the area is added to the glacier layer and in a

second step the glacier flow is simulated by using a modified D8 technique

(submodule :code:`fracd8`).

Since the prupose of the D8 flow direction algorithm is modeling surface water

flows over terrain, the D8 algorithm was modified to be able to consider the

fraction of ice that is flowing out of each cell based on the glaciers

velocity. In order to avoid pure convergence of the flow, the surface of the

glaciers is slightly smoothed. The simulation stops when the observed

difference in mass balance for a smoothed curve (default

:code:`MODEL_TREND_SIZE=100`) is less than a given tolerance (default

:code:`MODEL_TOLERANCE=0.0001`).



Getting started

---------------



The **glacier-flow-model** package depends on GDAL, which needs to be installed

on the system.



Get the stable release of the package from pypi:



.. code-block:: shell



    pip install glacier-flow-model



Example data

____________



The package includes an example DEM from `swisstopo `_.

It covers a smaller extent around the Aletsch glacial arena in Switzerland with

a raster cell resolution of 200m.



.. code-block:: python



    from glacier_flow_model import PkgDataAccess

    dem = PkgDataAccess.load_dem()



The original DEM can be downloaded `here `_.



Usage

_____



To set up a glacier flow model, a path to a DEM in the GeoTiff file format has

to passed to the model class constructor. By default the mass balance

parameters for alpine glaciers in the year 2000 are set. Keep the input file

size small, otherwise the model may be slowed down remarkably:



.. code-block:: python



    import logging

    from glacier_flow_model import GlacierFlowModel, PkgDataAccess



    LOG_FORMAT = "[%(asctime)s %(levelname)s] %(message)s (%(name)s)"

    logging.basicConfig(format=LOG_FORMAT, level=logging.INFO)



    gfm = GlacierFlowModel(PkgDataAccess.locate_dem())



After initialization, the model needs to accumulate the initial ice mass until

it reaches a steady state, call the :code:`reach_steady_state` method to do so:



.. code-block:: python



    gfm.reach_steady_state()



.. image:: https://raw.githubusercontent.com/munterfi/glacier-flow-model/master/docs/source/_static/steady_state_initial.png

   :alt: https://github.com/munterfi/glacier-flow-model

   :align: center



When the model is in a steady state, a temperature change of the climate can be

simulated. Simply use the :code:`simulate` method with a positive or negative

temperature change in degrees. The model changes the temperature gradually and

simulates years until it reaches a steady state again.



Heating 4.5°C after initial steady state:



.. code-block:: python



    gfm.simulate(4.5)



.. image:: https://raw.githubusercontent.com/munterfi/glacier-flow-model/master/docs/source/_static/steady_state_heating.png

   :alt: https://github.com/munterfi/glacier-flow-model

   :align: center



Cooling -3°C after initial steady state:



.. code-block:: python



    gfm.simulate(-3)



.. image:: https://raw.githubusercontent.com/munterfi/glacier-flow-model/master/docs/source/_static/steady_state_cooling.png

   :alt: https://github.com/munterfi/glacier-flow-model

   :align: center



Export the results of the model into :code:`.csv` and :code:`.tif` files:



.. code-block:: python



    gfm.export()



The GeoTiff contains the following bands, averaged over the last 10 simulation

years (default :code:`MODEL_RECORD_SIZE=10`):



1. Glacier thickness [m].

2. Velocity at medium height [m/a].

3. Mass balance [m].



Check out the `video `_ of the scenario simulation in the Aletsch

glacial arena in Switzerland



Limitations

-----------



The model has some limitations that need to be considered:



- The flow velocity of the ice per year is limited by the resolution of the

  grid cells. Therefore, a too high resolution should not be chosen for the

  simulation.

- The modeling of ice flow is done with D8, a technique for modeling surface

  flow in hydrology. Water behaves fundamentally different from ice, which is

  neglected by the model (e.g. influence of crevasses).

- The flow velocity only considers internal ice deformation (creep). Basal

  sliding, and soft bed deformation are ignored.

- No distinction is made between snow and ice. The density of the snow or ice

  mass is also neglected in the vertical column.



License

-------



This project is licensed under the MIT License - see the LICENSE file for

details