jSnow17

Dual-backend (JAX + NumPy) implementation of the Snow-17 temperature-index snow accumulation and ablation model, with functional and BMI interfaces.

Part of the SYMFLUENCE JAX-native model family — self-contained packages that run standalone (NumPy fallback, no JAX required) and register automatically with SYMFLUENCE when installed alongside it.

Features

• Differentiable: automatic differentiation through the full simulation (JAX)
• Fast: JIT compilation via lax.scan; vmap for ensembles; GPU-capable
• Dependency-light: pure-NumPy fallback when JAX is not installed
• Plugin architecture: auto-registers with SYMFLUENCE via entry points

Installation

pip install jsnow17          # NumPy backend
pip install 'jsnow17[jax]'    # with JAX (differentiable, JIT)

Quickstart

from jsnow17 import Snow17BMI, snow17_simulate

# functional interface (JAX-compatible, differentiable)
rain_plus_melt, state = snow17_simulate(precip, temp, doy, params, lat=51.17)

# BMI interface for model coupling
snow = Snow17BMI(params={"SCF": 1.1}, latitude=51.17)
snow.initialize()
rpm = snow.update(precip_t, temp_t, doy_t)

Use with SYMFLUENCE

Within SYMFLUENCE, jSnow17 is the snow component coupled to rainfall–runoff packages such as jSACSMA and jXAJ; it is installed automatically as their dependency and is not selected as a standalone model.

Model structure

Snow-17 (Anderson, 1973, 2006) with all branching expressed through smooth where operations for JAX differentiability:

1. Rain/snow partitioning via PXTEMP with a 2 °C mixed-phase transition
2. Snowfall gauge-undercatch correction (SCF)
3. Hemisphere-aware seasonal melt-factor sinusoid
4. Non-rain and rain-on-snow melt
5. Heat-deficit tracking (TIPM-weighted antecedent temperature)
6. Liquid-water routing with PLWHC capacity and refreezing
7. Areal depletion curve
8. Daily ground melt (DAYGM)

11 calibration parameters (jsnow17.parameters.PARAM_BOUNDS).

Testing

pip install -e '.[dev]'
pytest

How to cite

If you use jSnow17 in your research, please cite the SYMFLUENCE companion papers, which describe the design of the JAX-native model family (registry integration, differentiability, and the calibration experiments they enable):

Eythorsson, D., et al. (2026). The registry as social contract: Architectural patterns for community hydrological modeling. Water Resources Research (submitted).

Eythorsson, D., et al. (2026). From configuration to prediction: Multi-model, multi-basin experiments with SYMFLUENCE. Water Resources Research (submitted).

Citation metadata for this package is provided in CITATION.cff; a version-specific DOI is minted via Zenodo for each GitHub release.

References

• Anderson, E. A. (1973). National Weather Service River Forecast System — Snow Accumulation and Ablation Model. NOAA Technical Memorandum NWS HYDRO-17.
• Anderson, E. A. (2006). Snow Accumulation and Ablation Model — SNOW-17. NOAA Technical Report NWS HYDRO-17.

License

Apache-2.0. See LICENSE.