Neural-LAM is a repository of graph-based neural weather prediction models for Limited Area Modeling (LAM). Also global forecasting is possible, but currently on a different branch (planned to be merged with main). The code uses PyTorch and PyTorch Lightning. Graph Neural Networks are implemented using PyG and logging is set up through Weights & Biases.

The repository contains LAM versions of:

• The graph-based model from Keisler (2022).
• GraphCast, by Lam et al. (2023).
• The hierarchical model from Oskarsson et al. (2023).

Publications

For a more in-depth scientific introduction to machine learning for LAM weather forecasting see the publications listed here. As the code in the repository is continuously evolving, the latest version might feature some small differences to what was used for these publications. We retain some paper-specific branches for reproducibility purposes.

If you use Neural-LAM in your work, please cite the relevant paper(s).

Graph-based Neural Weather Prediction for Limited Area Modeling

@inproceedings{oskarsson2023graphbased,
    title={Graph-based Neural Weather Prediction for Limited Area Modeling},
    author={Oskarsson, Joel and Landelius, Tomas and Lindsten, Fredrik},
    booktitle={NeurIPS 2023 Workshop on Tackling Climate Change with Machine Learning},
    year={2023}
}

See the branch ccai_paper_2023 for a revision of the code that reproduces this workshop paper.

Probabilistic Weather Forecasting with Hierarchical Graph Neural Networks

@inproceedings{oskarsson2024probabilistic,
  title = {Probabilistic Weather Forecasting with Hierarchical Graph Neural Networks},
  author = {Oskarsson, Joel and Landelius, Tomas and Deisenroth, Marc Peter and Lindsten, Fredrik},
  booktitle = {Advances in Neural Information Processing Systems},
  volume = {37},
  year = {2024},
}

See the branches prob_model_lam and prob_model_global for revisions of the code that reproduces this paper. The global and probabilistic models from this paper are not yet fully merged with main (see issues 62 and 63).

Modularity

The Neural-LAM code is designed to modularize the different components involved in training and evaluating neural weather prediction models. Models, graphs and data are stored separately and it should be possible to swap out individual components. Still, some restrictions are inevitable:

• The graph used has to be compatible with what the model expects. E.g. a hierarchical model requires a hierarchical graph.
• The graph and data are specific to the limited area under consideration. This is of course true for the data, but also the graph should be created with the exact geometry of the area in mind.

A note on the limited area setting

Currently we are using these models on a limited area covering the Nordic region, the so called MEPS area (see paper). There are still some parts of the code that is quite specific for the MEPS area use case. This is in particular true for the mesh graph creation (python -m neural_lam.create_mesh) and some of the constants set in a data_config.yaml file (path specified in python -m neural_lam.train_model --data_config <data-config-filepath> ). There is ongoing efforts to refactor the code to be fully area-agnostic. See issues 4 and 24 for more about this. See also the weather-model-graphs package for constructing graphs for arbitrary areas.

Using Neural-LAM

Below follows instructions on how to use Neural-LAM to train and evaluate models.

Installation

When installing neural-lam you have a choice of either installing with directly pip or using the pdm package manager. We recommend using pdm as it makes it easy to add/remove packages while keeping versions consistent (it automatically updates the pyproject.toml file), makes it easy to handle virtual environments and includes the development toolchain packages installation too.

regarding torch installation: because torch creates different package variants for different CUDA versions and cpu-only support you will need to install torch separately if you don't want the most recent GPU variant that also expects the most recent version of CUDA on your system.

We cover all the installation options in our github actions ci/cd setup which you can use as a reference.

Using pdm

1. Clone this repository and navigate to the root directory.
2. Install pdm if you don't have it installed on your system (either with pip install pdm or following the install instructions).

If you are happy using the latest version of torch with GPU support (expecting the latest version of CUDA is installed on your system) you can skip to step 5.

3. Create a virtual environment for pdm to use with pdm venv create --with-pip.
4. Install a specific version of torch with pdm run python -m pip install torch --index-url https://download.pytorch.org/whl/cpu for a CPU-only version or pdm run python -m pip install torch --index-url https://download.pytorch.org/whl/cu111 for CUDA 11.1 support (you can find the correct URL for the variant you want on PyTorch webpage).
5. Install the dependencies with pdm install (by default this in include the). If you will be developing neural-lam we recommend to install the development dependencies with pdm install --group dev. By default pdm installs the neural-lam package in editable mode, so you can make changes to the code and see the effects immediately.

Using pip

1. Clone this repository and navigate to the root directory.

If you are happy using the latest version of torch with GPU support (expecting the latest version of CUDA is installed on your system) you can skip to step 3.

2. Install a specific version of torch with python -m pip install torch --index-url https://download.pytorch.org/whl/cpu for a CPU-only version or python -m pip install torch --index-url https://download.pytorch.org/whl/cu111 for CUDA 11.1 support (you can find the correct URL for the variant you want on PyTorch webpage).
3. Install the dependencies with python -m pip install .. If you will be developing neural-lam we recommend to install in editable mode and install the development dependencies with python -m pip install -e ".[dev]" so you can make changes to the code and see the effects immediately.

Data

Datasets should be stored in a directory called data. See the repository format section for details on the directory structure.

The full MEPS dataset can be shared with other researchers on request, contact us for this. A tiny subset of the data (named meps_example) is available in example_data.zip, which can be downloaded from here. Download the file and unzip in the neural-lam directory. Graphs used in the initial paper are also available for download at the same link (but can as easily be re-generated using python -m neural_lam.create_mesh). Note that this is far too little data to train any useful models, but all pre-processing and training steps can be run with it. It should thus be useful to make sure that your python environment is set up correctly and that all the code can be ran without any issues.

Pre-processing

An overview of how the different pre-processing steps, training and files depend on each other is given in this figure:

In order to start training models at least three pre-processing steps have to be run:

• python -m neural_lam.create_mesh
• python -m neural_lam.create_grid_features
• python -m neural_lam.create_parameter_weights

Create graph

Run python -m neural_lam.create_mesh with suitable options to generate the graph you want to use (see python neural_lam.create_mesh --help for a list of options). The graphs used for the different models in the paper can be created as:

• GC-LAM: python -m neural_lam.create_mesh --graph multiscale
• Hi-LAM: python -m neural_lam.create_mesh --graph hierarchical --hierarchical (also works for Hi-LAM-Parallel)
• L1-LAM: python -m neural_lam.create_mesh --graph 1level --levels 1

The graph-related files are stored in a directory called graphs.

Create remaining static features

To create the remaining static files run python -m neural_lam.create_grid_features and python -m neural_lam.create_parameter_weights.

Weights & Biases Integration

The project is fully integrated with Weights & Biases (W&B) for logging and visualization, but can just as easily be used without it. When W&B is used, training configuration, training/test statistics and plots are sent to the W&B servers and made available in an interactive web interface. If W&B is turned off, logging instead saves everything locally to a directory like wandb/dryrun.... The W&B project name is set to neural-lam, but this can be changed in the flags of python -m neural_lam.train_model (using argsparse). See the W&B documentation for details.

If you would like to login and use W&B, run:

wandb login

If you would like to turn off W&B and just log things locally, run:

wandb off

Train Models

Models can be trained using python -m neural_lam.train_model. Run python neural_lam.train_model --help for a full list of training options. A few of the key ones are outlined below:

• --dataset: Which data to train on
• --model: Which model to train
• --graph: Which graph to use with the model
• --processor_layers: Number of GNN layers to use in the processing part of the model
• --ar_steps: Number of time steps to unroll for when making predictions and computing the loss

Checkpoints of trained models are stored in the saved_models directory. The implemented models are:

Graph-LAM

This is the basic graph-based LAM model. The encode-process-decode framework is used with a mesh graph in order to make one-step pedictions. This model class is used both for the L1-LAM and GC-LAM models from the paper, only with different graphs.

To train 1L-LAM use

python -m neural_lam.train_model --model graph_lam --graph 1level ...

To train GC-LAM use

python -m neural_lam.train_model --model graph_lam --graph multiscale ...

Hi-LAM

A version of Graph-LAM that uses a hierarchical mesh graph and performs sequential message passing through the hierarchy during processing.

To train Hi-LAM use

python -m neural_lam.train_model --model hi_lam --graph hierarchical ...

Hi-LAM-Parallel

A version of Hi-LAM where all message passing in the hierarchical mesh (up, down, inter-level) is ran in parallel. Not included in the paper as initial experiments showed worse results than Hi-LAM, but could be interesting to try in more settings.

To train Hi-LAM-Parallel use

python -m neural_lam.train_model --model hi_lam_parallel --graph hierarchical ...

Checkpoint files for our models trained on the MEPS data are available upon request.

Evaluate Models

Evaluation is also done using python -m neural_lam.train_model, but using the --eval option. Use --eval val to evaluate the model on the validation set and --eval test to evaluate on test data. Most of the training options are also relevant for evaluation (not ar_steps, evaluation always unrolls full forecasts). Some options specifically important for evaluation are:

• --load: Path to model checkpoint file (.ckpt) to load parameters from
• --n_example_pred: Number of example predictions to plot during evaluation.

Note: While it is technically possible to use multiple GPUs for running evaluation, this is strongly discouraged. If using multiple devices the DistributedSampler will replicate some samples to make sure all devices have the same batch size, meaning that evaluation metrics will be unreliable. A possible workaround is to just use batch size 1 during evaluation. This issue stems from PyTorch Lightning. See for example this PR for more discussion.

Repository Structure

Except for training and pre-processing scripts all the source code can be found in the neural_lam directory. Model classes, including abstract base classes, are located in neural_lam/models.

Format of data directory

It is possible to store multiple datasets in the data directory. Each dataset contains a set of files with static features and a set of samples. The samples are split into different sub-directories for training, validation and testing. The directory structure is shown with examples below. Script names within parenthesis denote the script used to generate the file.

data
├── dataset1
│   ├── samples                             - Directory with data samples
│   │   ├── train                           - Training data
│   │   │   ├── nwp_2022040100_mbr000.npy  - A time series sample
│   │   │   ├── nwp_2022040100_mbr001.npy
│   │   │   ├── ...
│   │   │   ├── nwp_2022043012_mbr001.npy
│   │   │   ├── nwp_toa_downwelling_shortwave_flux_2022040100.npy   - Solar flux forcing
│   │   │   ├── nwp_toa_downwelling_shortwave_flux_2022040112.npy
│   │   │   ├── ...
│   │   │   ├── nwp_toa_downwelling_shortwave_flux_2022043012.npy
│   │   │   ├── wtr_2022040100.npy          - Open water features for one sample
│   │   │   ├── wtr_2022040112.npy
│   │   │   ├── ...
│   │   │   └── wtr_202204012.npy
│   │   ├── val                             - Validation data
│   │   └── test                            - Test data
│   └── static                              - Directory with graph information and static features
│       ├── nwp_xy.npy                      - Coordinates of grid nodes (part of dataset)
│       ├── surface_geopotential.npy        - Geopotential at surface of grid nodes (part of dataset)
│       ├── border_mask.npy                 - Mask with True for grid nodes that are part of border (part of dataset)
│       ├── grid_features.pt                - Static features of grid nodes (neural_lam.create_grid_features)
│       ├── parameter_mean.pt               - Means of state parameters (neural_lam.create_parameter_weights)
│       ├── parameter_std.pt                - Std.-dev. of state parameters (neural_lam.create_parameter_weights)
│       ├── diff_mean.pt                    - Means of one-step differences (neural_lam.create_parameter_weights)
│       ├── diff_std.pt                     - Std.-dev. of one-step differences (neural_lam.create_parameter_weights)
│       ├── flux_stats.pt                   - Mean and std.-dev. of solar flux forcing (neural_lam.create_parameter_weights)
│       └── parameter_weights.npy           - Loss weights for different state parameters (neural_lam.create_parameter_weights)
├── dataset2
├── ...
└── datasetN

Format of graph directory

The graphs directory contains generated graph structures that can be used by different graph-based models. The structure is shown with examples below:

graphs
├── graph1                                  - Directory with a graph definition
│   ├── m2m_edge_index.pt                   - Edges in mesh graph (neural_lam.create_mesh)
│   ├── g2m_edge_index.pt                   - Edges from grid to mesh (neural_lam.create_mesh)
│   ├── m2g_edge_index.pt                   - Edges from mesh to grid (neural_lam.create_mesh)
│   ├── m2m_features.pt                     - Static features of mesh edges (neural_lam.create_mesh)
│   ├── g2m_features.pt                     - Static features of grid to mesh edges (neural_lam.create_mesh)
│   ├── m2g_features.pt                     - Static features of mesh to grid edges (neural_lam.create_mesh)
│   └── mesh_features.pt                    - Static features of mesh nodes (neural_lam.create_mesh)
├── graph2
├── ...
└── graphN

Mesh hierarchy format

To keep track of levels in the mesh graph, a list format is used for the files with mesh graph information. In particular, the files

│   ├── m2m_edge_index.pt                   - Edges in mesh graph (neural_lam.create_mesh)
│   ├── m2m_features.pt                     - Static features of mesh edges (neural_lam.create_mesh)
│   ├── mesh_features.pt                    - Static features of mesh nodes (neural_lam.create_mesh)

all contain lists of length L, for a hierarchical mesh graph with L layers. For non-hierarchical graphs L == 1 and these are all just singly-entry lists. Each entry in the list contains the corresponding edge set or features of that level. Note that the first level (index 0 in these lists) corresponds to the lowest level in the hierarchy.

In addition, hierarchical mesh graphs (L > 1) feature a few additional files with static data:

├── graph1
│   ├── ...
│   ├── mesh_down_edge_index.pt             - Downward edges in mesh graph (neural_lam.create_mesh)
│   ├── mesh_up_edge_index.pt               - Upward edges in mesh graph (neural_lam.create_mesh)
│   ├── mesh_down_features.pt               - Static features of downward mesh edges (neural_lam.create_mesh)
│   ├── mesh_up_features.pt                 - Static features of upward mesh edges (neural_lam.create_mesh)
│   ├── ...

These files have the same list format as the ones above, but each list has length L-1 (as these edges describe connections between levels). Entries 0 in these lists describe edges between the lowest levels 1 and 2.

Development and Contributing

Any push or Pull-Request to the main branch will trigger a selection of pre-commit hooks. These hooks will run a series of checks on the code, like formatting and linting. If any of these checks fail the push or PR will be rejected. To test whether your code passes these checks before pushing, run

pre-commit run --all-files

from the root directory of the repository.

Furthermore, all tests in the tests directory will be run upon pushing changes by a github action. Failure in any of the tests will also reject the push/PR.

Contact

If you are interested in machine learning models for LAM, have questions about the implementation or ideas for extending it, feel free to get in touch. There is an open mllam slack channel that anyone can join (after following the link you have to request to join, this is to avoid spam bots). You can also open a github issue on this page, or (if more suitable) send an email to joel.oskarsson@liu.se.