Code for the manuscript "Cell tracking -based framework for assessing nowcasting model skill in reproducing growth and decay of convective rainfall" by Ritvanen et al.

This repository contains code for the manuscript

Ritvanen, J., Pulkkinen, S., Moisseev, D., Nerini, D. (2024): Cell tracking -based framework for assessing nowcasting model skill in reproducing growth and decay of convective rainfall

submitted to the Geoscientific Model Development journal.

Python environment

For installing the conda environment for running the pysteps nowcasts and cell tracking analysis, run

bash conda env create -f environment_proc.yml

For installing the conda environment for plotting the figures with the notebooks, run

bash conda env create -f environment_jupyter.yml

Replicating pysteps nowcasts

1. Create a section in the pystepsrc file for your data source. For more information, refer to the existing sections or the pysteps documentation.
2. Update configuration files in config/swiss-data/pysteps directory
   • hdf5_path to the output filepath
   • datelist_path to the file containing the list of dates to process
   • data_source_name to the name of the data source in the pystepsrc file
   • as required, the attributes that are written to output file under save:what_attrs
3. Run the nowcasting script with the configuration file folder as an argument

```bash conda activate proc export PYTHONPATH=$PYTHONPATH:. export OMPNUMTHREADS=1

python scripts/runpystepsswap_predictions.py swiss-data/pysteps-predictions ```

The script will run the nowcasts for all configuration files in the provided folder. If necessary, move the configuration files to another folder to run only a subset of the configurations.

Storing the measurement data

1. Create a section in the pystepsrc file for your data source. For more information, refer to the existing sections or the pysteps documentation.
2. Update the paths in the config/swiss-data/save_measurements.yaml file
   • hdf5_path to the output filepath
   • datelist_path to the file containing the list of dates to process
   • data_source_name to the name of the data source in the pystepsrc file
   • as required, the attributes that are written to output file under save:what_attrs
3. Run the script to save the measurements

```bash conda activate proc

export PYTHONPATH=$PYTHONPATH:. export OMPNUMTHREADS=1

python scripts/savemeasurements.py config/swiss-data/savemeasurements.yaml ```

For both the nowcasts and measurements, the values are packed into an 8-bit format using a lookup table. The lookup table is stored in the verif/metranet_lookup.py file. If you wish to disable this behaviour and instead pack using a specified gain and offset values, set use_metranet_lookup to False in the configuration file and instead provide the gain and offset values.

Running the cell tracking verification framework

The cell tracking verification expects input data in the HDF5 format. The data should have the following structure for the observation files:

txt ├YYYY-mm-dd HH:MM:SS │ └measurements │ ├data [uint8: HEIGHT × WIDTH] │ │ └2 attributes: │ │ ├CLASS: b'IMAGE' │ │ └IMAGE_VERSION: b'1.2' │ └what │ └N attributes: │ ...

where the <YYYY-mm-dd HH:MM:SS>/data is the dataset containing the rainrate values in mm/h. The data should be stored as an 8-bit integer with a lookup table to convert the values to the original scale. If the data is instead stored in 8-bit format with gain and offset, make sure that the gain and offset values are provided as attributes in <YYYY-mm-dd HH:MM:SS>/data/what and that <YYYY-mm-dd HH:MM:SS>/data/what/use_metranet_lookup attribute is false.

The nowcasts are expected to be stored in the following structure:

txt ├YYYY-mm-dd HH:MM:SS <model-name> ├<leadtime-index> │ ├data [uint8: WIDTH × HEIGHT] │ │ └2 attributes: │ │ ├CLASS: b'IMAGE' │ │ └IMAGE_VERSION: b'1.2' │ └what │ N attributes: │ .... ├<leadtime-index> │ ├data [uint8: WIDTH × HEIGHT] │ │ └2 attributes: │ │ ├CLASS: b'IMAGE' │ │ └IMAGE_VERSION: b'1.2' │ └what │ N attributes: ...

where the <YYYY-mm-dd HH:MM:SS>/data/<i> is the dataset containing the nowcast for leadtime step <i> values in mm/h. The data should be stored as an 8-bit integer with a lookup table to convert the values to the original scale. If the data is instead stored in 8-bit format with gain and offset, make sure that the gain and offset values are provided as attributes in <YYYY-mm-dd HH:MM:SS>/data/<i>/what and that <YYYY-mm-dd HH:MM:SS>/data/<i>/what/use_metranet_lookup attribute is false.

Next, update the configuration file config/swiss-data/calculate_metrics_objects.yaml:

• exp_id to the experiment identifier
• path:root to the output directory root
• path:metrics: to the output file location for the metrics
• path:states: to the output file location for the verification state
• path:timestamps: to the list of timestamps to process
• path:done: the path to the CSV file recording which metrics have been calculated
• path:config_copy: the path to the configuration file copy
• path:logging: the path to the log file
• methods items for each nowcast method with the structure

yaml <model-name>: path: <path-to-hdf5-file>

• measurements with the following structure

yaml measurements: name: measurements path: <path-to-hdf5-file>

• if required, update the cell tracking parameters in the metrics:OBJECTS:init_kwargs section:
  • leadtimes to the list of leadtimes to process
  • prev_obs_times: the number of previous timesteps to load (i.e, t-1, t-2, ...)
  • zr_a and zr_b to the Z-R relationship parameters used to transform to reflectivity values
  • dist_limit_matching to the maximum distance for matching cells in the Hungarian algorithm, in pixel units
  • tdating_kwargs to the parameters for the t-dating algorithm. For more information, refer to pysteps documentation

After that, run the script to calculate the metrics

```bash conda activate proc

export PYTHONPATH=$PYTHONPATH:.

python scripts/calculatemetrics.py config/swiss-data/calculatemetrics_objects.yaml ```

Plotting the figures

To plot the results, first set the configuration file config/swiss-data/plot_metrics_objects.yaml:

• exp_id to the experiment identifier
• path:result_dir to the output directory root
• stylefile path to the stylefile for the plots
• legend_order a list specifying the order of the models in figure legends
• metric_conf for each metric specify e.g. the y axis limits and label names
• methods each model to be plotted in the following structure

yaml <model-name>: color: "<model-color-name-or-hex-code" label: "<model-label>" linestyle: "<model-linestyle>"

For running the notebooks, use the jupyter conda environment. The notebooks are located in the notebooks directory. It is recommended to start the jupyter server in the root directory of the repository, otherwise some paths to stylefiles and configuration files need to be updated in the notebooks.

```bash conda activate jupyter export PYTHONPATH=$PYTHONPATH:.

jupyter lab ```

The figures can be plotted with the following notebooks:

• notebooks/cell_verification_article_figures.ipynb for all result figures in the article, except Figure 12 (number of splits and merges)
• notebooks/cell_verification_article_splits_merges.ipynb for Figure 12 (number of splits and merges)
• notebooks/cell_verification_article_supplementary_figures.ipynb for supplementary figures
• notebooks/plot_domain_figure.ipynb for plotting the domain figure. Update the path to the topography data in the 4th cell in the notebook.
• notebooks/plot_pixel_csi_rmse.ipynb for plotting the pixel-wise CSI and RMSE figures. Note that this notebook uses the

The nowcast figure can be plotted with the script scripts/plot_nowcast_figures.py that uses the configuration file config/swiss-data/plot_nowcast_figs.yaml. To update the configuration file, refer to the comments in the file. The script can be run with

```bash conda activate proc

export PYTHONPATH=$PYTHONPATH:.

python scripts/plotnowcastfigures.py config/swiss-data/plotnowcastfigs.yaml ```

where <YYYYMMMDDHHMM> is the timestamp to plot.

Note that, as the configuration file is provided here, the observations are read from the original metranet data file, so plotting the nowcasts requires the original metranet data file to be available and the py-radlib package to be installed. Also ODIM compliant HDF5 files are supported; in this case, change the input_data:RATE:reader_func to h5_to_dataset.

License

The code is licensed under the MIT license. See the LICENSE file for more information.