Groundwater response models with Pastas

Use Pastas for a well's response to time-varying stresses. Fitted response parameters are effective model parameters; they do not by themselves establish transmissivity, aquifer geometry or hydraulic connectivity. Use FloPy/MODFLOW for a supported spatial-flow question.

This entrypoint targets Pastas 2.0. Its component constructors accept the owning model and register themselves; older add_stressmodel patterns are being retired. Use the tested dependency baseline for reproducible work. The 2.0 package also needs tqdm for its imported solver timer in the checked environment.

Prepare data and reserve evaluation dates

Record the head unit and vertical reference, well/screen, timestamp convention, stress units and whether evaporation is measured or estimated reference potential evaporation. A negative relative head or depth-to-water series is not automatically elevation above sea level. Preserve the original datum.

For daily recharge models use consistently converted head (m), precipitation and reference evaporation (mm/day). Preserve daily accumulation labels; do not invent a timezone or shift dates without knowing the observation support. Missing rainfall is not zero. Keep head gaps unfilled, check stress coverage through the model warmup, and record any stress infilling with its calibration source. Pastas defaults can fill and extend stresses, so make these choices explicit before constructing the model.

Fix calibration and holdout dates before fitting. Construct the model using calibration heads and stresses only, including data-derived initial values. Future observed stresses may support a hindcast; future observed heads must not adjust fitted parameters or simulated state. A forecast additionally needs specified future stress scenarios and uncertainty.

Calibrate a checked recharge model

This function expects unique, ordered daily-date Series, complete nonnegative stresses covering the requested observed warmup, and at least three finite calibration heads. Those input checks are enforced by the bundled helper.

import pastas as ps

def fit_recharge(calibration_head, calibration_precip, calibration_evap,
                 start, end, warmup_days):
    model = ps.Model(calibration_head, name='well')
    settings = {'freq': 'D', 'sample_up': 'bfill', 'sample_down': 'mean',
                'fill_nan': None, 'fill_before': None, 'fill_after': None}
    ps.RechargeModel(model, calibration_precip, calibration_evap,
                     rfunc=ps.Gamma(), recharge=ps.rch.Linear(), name='recharge',
                     settings=(settings.copy(), settings.copy()))
    ps.ArNoiseModel(model)
    model.solve(tmin=start, tmax=end, warmup=warmup_days, report=False)
    if not model.solver.result.success:
        raise RuntimeError('Calibration did not converge')
    return model

The calibration helper validates CSV shape, dates, explicit calibration windows and stress coverage, then saves .pas with model.to_file(...). Plotting is optional. It assumes already normalized units; it does not guess them from column names or perform missing-stress fills.

python scripts/groundwater_model.py head_m.csv rain_mm_day.csv evap_mm_day.csv \
  --calibration-start 2005-01-01 --calibration-end 2013-12-31 \
  --warmup-days 730 --noise --output fitted.pas

Resolve the script relative to this installed skill directory. A calibrated file is not a completed holdout evaluation: report baselines, independent observed-date metrics and residuals using the fixed evaluation period.

Contributions, diagnostics and persistence

model.get_contributions() returns a list of Series, possibly split into precipitation and evaporation components. Iterate the list or request one combined contribution with model.get_contribution('recharge'); do not call .items() on it. Add the fitted constant when checking the total simulation. A block response represents a finite-duration stress block, not an instantaneous impulse. Use model.get_step_response and model.get_block_response accordingly.

Save with model.to_file('model.pas'), reload with ps.io.load('model.pas'), and compare simulations on the same date window. There is no Model.to_json method in the checked API. Adding ps.ArNoiseModel(model) is distinct from merely passing a noise=True solver flag.

Use ps.stats.acf(residuals, lags=[1, 7, 30], bin_method='gaussian') when observations have gaps; specify lag units in days and inspect pair counts. Residual and noise-series diagnostics answer different questions. AIC/BIC comparison requires the same observations/objective, and a universal EVP>70% threshold is not a validation criterion. Persistent innovation correlation limits confidence in conventional parameter standard errors.

Read stress configuration for pumping/river inputs and nonlinear recharge, or response interpretation for parameter signs, units and response tails. These conditional structures need their own data and diagnostics.

Executed scope

The project's hydrogeological workflow runs a fixed public USGS/GSOD recharge hindcast with Pastas 2.0: QC, calibration-only fitting, three baselines, residual ACF, continuous holdout simulation and save/load readback. The helper's daily recharge path and pumping-response sign also have real-library checks. This does not validate every nonlinear, multiwell or uncertainty configuration.

Official Pastas 2.0 release, versioned model API source, checked 2026-09-15.