A simple parametrisation of the transport and deposition of snow on steep terrains.

The snowslide python package was written by Guillem Carcanade, intern in the glaciology team of IGE Grenoble based on the algorithms described by Bernhardt & Schulz, 2010 and Gruber, 2007.

This package provides a simple parametrisation of the transport and deposition of snow in mountain terrains. It has been designed for applications in glaciological modeling, and specifically to be used through the OGGM workflow. While the package provides methods for use in conjunction with OGGM, the basic functions can also be called up and used independently. Snowslide can then work in a wide variety of context that includes gravitational transport. Snowslide operates the estimated redistribution of snow by avalanches using only two inputs :

• a dem given as a path to a .tif file
• information about initial snow depths

The next steps goes into more details about how snowslide works and should be used.

Installation

Snowslide relies on basic python librairies for data manipulation. Nonetheless, the routing of the snow is calculated by an external python module called pysheds (docs : https://github.com/mdbartos/pysheds/). Running snowslide therefore requires installing pysheds (pip install pysheds).

We recommend using SnowSlide with python version 3.10.

The list of all snowslide dependancies is given as follow :

• pysheds 0.3.5 or 0.5 (see the note below)
• rasterio 1.3.10
• numpy 1.26.4
• xarray 2024.3.0
• pandas 2.2.3
• matplotlib 3.8.4
• os
• datetime
• netcdf4d
• h5netcdf
• imageio (only for snowslide_complete)

pysheds 0.5: older versions of snowslide do not route snow correctly with pysheds 0.5 (flow directions on the DEM edges and nodata values: on the example DEM, mfd lost most of the snow and d8 created snow). This is fixed in dem_flow(), which now sets nodata_out=0 and allows no flow from or to the DEM edges.

These libraries must be installed to run snowslide. Then you can install snowslide using pip :

$ pip install -e git+https://github.com/MarinKneib/Snowslide.git#egg=snowslide

This should clone the snowslide GitHub repository and install it as a python package in the active virtual environment chosen.

If you also want to use Snowslide with OGGM you will also need to install OGGM and the corresponding dependencies (https://docs.oggm.org/en/stable/installing-oggm.html)

Package structure

Directory root (./)

• .gitignore: for git users only
• LICENSE.txt: (https://help.github.com/articles/licensing-a-epository/) license of the code
• README.md: this page
• pyproject.toml: this is what makes your package insallable by pip. It contains a set of simple instructions regarding e.g. the name of the package, its version number, or where to find command line scripts.

The actual package (./snowslide)

• __init__.py: tells python that the directory is a package and enables the "dotted module names" import syntax. It is often empty,fla but here we added some entry points to the package's API and the version string.
• snowslide_main.py: main module that operates the simulation
• functions.py: various functions used in the main module and defined separatly
• display_2Dresults.py: very basic display functionalities ofered to the user
• display_3Dresults.py: very basic display functionalities ofered to the user (Disabled for now)
• oggm_snowslide_compat.py: module recognised as a task by OGGM and used to launch snowslide through a workflow using OGGM. This allows snowslide to use all the possibilities offered by OGGM.
  (see after)
• oggm_snowslide_compat_minimal.py: reduced version of oggm_snowslide_compat.py (avalanche tasks, monthly avalanche mass-balance model and its calibration)
• oggm_snowslide_compat_minimal_oggm_dev_v163.py: version for OGGM 1.6.3.dev (tested with commit 27ba8ed65), with the daily, surface-type and debris avalanche mass-balance models

The tests (./snowslide/test)

test_snowslide.py: is a module that can be detected by pytest. It includes various functions that test the expected behaviour of snowslide algorithm. ./data : contains basic data to run the tests

Snowslide Features

Through a main function defined in snowslide_main, snowslide uses a number of functions which are present in the functions.py file. These are the following :

• dem_flow() : This function can preprocess the dem (or not) and compute the flow direction based on the total elevation surface (dem + snow depth)
• precipitations_base() : This function initialize an ideal SND matrix based on solid precipitation information
• slope() : This function calculate a slope matrix based on the dem matrix
• snow_routing() : That function routes the snow based on the routing method chosen ('mfd' or 'd8'). It is called at each iteration.
• SND_max_exponential(): Function that compute the maximal height of snow each pixel can store based on the slope. The function is an exponential and parameters are estimated from 'Bernhardt & Schulz 2007'.
• reframe_tif() : To quickly crop a DEM, retaining only the area of interest. It displays the initial DEM, and the user can then enter the x and y windows of the zone to be retained so that the function can store a new DEM entitled: 'reframed_dem'.
• resampling_dem() : This function allows to resample a dem to another resolution. It can be used to increase the speed of calculations if high resolution is not required.

The display_2Dresults.py and display_3Dresults.py are used in snowslide_complete() function defined in snowslide_main.py. This function offers the same simulation as snowslide_base(), but simply provides functions for recording and displaying output that can simplify the use of snowslide for the user in certain cases. We don't use it at the moment, so we recommend that users use the snowslide_base() function instead. The rest of the readme gives an example of using snowslide first in a snowslide workflow and then in an OGGM workflow.

How to use snowslide in a classic workflow ?

See the notebook How_to_use_snowslide.ipynb in the example folder

How to use snowslide in a OGGM workflow

See the notebook How_to_use_OGGMxSnowslide.ipynb in the example folder