Inferring parameters in a land surface model by combining data assimilation and machine learning

Authors: Lasse T. Keetz, Kristoffer Aalstad, Rosie A. Fisher

Special thanks to: Matvey Vladimirovich Debolskiy, Kaveh Karimi-Asli, the CTSM, FATES, and NorESM development teams, Cleary et al. (2021), FLUXNET, and the SMEAR II research network.

Code accompanying the research paper preliminarliy titled "Inferring parameters in a complex land surface model by combining data assimilation and machine learning" by Keetz et al. (in prep.). Adapts the approximate Bayesian inference framework termed "calibrate, emulate, sample" introduced by Cleary et al. (2021). Uncertainty-aware land surface model parameter estimation based on evapotranspiration and gross primary production flux observations. As a proof of concept, we assimilate single-site CLM-FATES outputs with (synthetic and real) eddy-covariance observations from a boreal forest site in southern Finland (Hyytil). The code currently relies on some hard-coded quick fixes and machine specific installations - use at own risk.

1 Installation instructions

Clone the repository.

git clone https://github.com/lasseke/fates-ces.git

1.1 Create and activate virtual environment

Install Mamba or Anaconda. Within the fates-ces directory, create a virtual environment with the Python dependencies via:

```

Optional: module load [nameofanaconda_module]

conda env create -f conda_env.yaml [-p env/installation/path] source activate fatescal-env [or env/installation/path] ```

This will also install the code in the repo's fatescal package in development mode.

1.2 (Optional) Install model

Edit the model_machine_config.txt file to specify the CLM-FATES model version and other details. Then run:

```

Assumes that git is installed and loaded!

python3 install_model.py

On SIGMA-2 machines, execute installmodelwith_modules.py for convenience

```

Note that your machine must be configured to run CLM-FATES. See https://escomp.github.io/ctsm-docs/versions/release-clm5.0/html/users_guide/overview/quickstart.html and the links therein to get started.

2 Running instructions

After successfully installing the software and its dependencies, several steps need to be completed before the parameter estimation can be executed. First, you need to create the CLM-FATES input and climate forcing data - refer to this shell script written for the create_data.py tool for inspiration. Next, you need to prepare the observational data that should be assimilated. Currently, this needs to be a csv file with a pandas.to_datetime()-compatible DateTime column (required to synchronize and resample the data) and one additional column per variable for the corresponding observations (see the Hyytil example files). The units and desired aggregation frequency must be specified in the config file (see below).

Many important workflow settings must be specified in the config.py file, such as the number of ensemble members, the path to the observational data file, the CTSM compset, etc. Follow the file layout specified in this example file.

2.1 Generate priors

Specify the prior settings (name of distribution, lower and upper bounds, default values, etc.) in fatescal/config.py. Then navigate to scripts/python/cesm_ensemble_runs/ and execute:

``` python3 01generatefatespriors.py -n [namestemofoutput_files]

For example:

python3 01generatefatespriors.py -n vcmaxbbslope_pm50percent ```

This will randomly draw N_ENSEMBLE_MEMBERS parameter sets from the specified prior distributions and store them in different file formats (.csv, .json, .pkl).

2.2 Run CES parameter estimation with CLM-FATES ensemble runs

In scripts/python/cesm_ensemble_runs/, run

python3 04_calibrate.py -n [name_stem_of_parameter_files]

where [name_stem_of_parameter_files] must correspond to the name stem chosen in step 2.1 (e.g.: vcmax_bbslope_pm50percent).

This script should then run all the required CES steps with the options defined in config.py. I.e.:

• Create, build, and submit a CLM-FATES multi-instance case with the specified model settings
• Wait for the ensemble simulations to finish on the HPC cluster
• Concatenate model outputs and align them with the observations
• Iteratively update the parameter sets (generated from the specified prior options) using the Iterative Ensemble-Kalman Smoother (IEnKS); within each iteration, rerun CLM-FATES with the updated parameters
• After the IEnKS updates are finished, train a machine learning emulator (Gaussian Process Regressor) on the resulting model-observation mismatches (-> negative log-likelihoods)
• Use the emulator to replace CLM-FATES as the forward model within an adaptive Markov Chain Monte Carlo algorithm -> enable systematic uncertainty quantification with the powerful MCMC method
• Create a final ensemble based on samples from the Markov chain and rerun CLM-FATES once again for evaluation

On Fram, building a multi-instance case with 128 ensemble members took ~1 h. Running a 20-year experiment (10 years for spin-up, 10 years for analysis, concatenating outputs, performing parameter updates) in Hyytil took ~3 hours per Kalman iteration.

Optional: Explore outputs

Refer to the ./notebooks directory for some result analysis examples.