Impact model: HyLake

Sector
Lakes (local)
Region
local, regional

HyLake v1.0 is a hybrid lake model that hard-couples a process-based one-dimensional surface energy balance and vertical thermal structure backbone with a Bayesian-Optimized Bidirectional LSTM (BO-BiLSTM) surrogate, which replaces the implicit Euler solver for lake surface temperature. The model was first developed and validated against FLake at five eddy-covariance sites in Lake Taihu (China), and tested for transferability at the ungauged Lake Chaohu, showing improved skill in surface temperature, latent heat flux, and sensible heat flux under both in-situ and ERA5-based forcing (He and Yang, 2025, Geosci. Model Dev., https://doi.org/10.5194/gmd-18-9257-2025).

Source code and data are openly available at https://doi.org/10.5281/zenodo.15289113.

HyLake v1.0 is the first version contributed to ISIMIP, used for ISIMIP4b runs. Ongoing development extends the surrogate-training base to ~900 globally distributed lakes for historical thermal-structure simulation, with future projections planned under CMIP6-based GCM forcing. This work will inform per-lake calibration for the Local Lakes sub-sector and provide the foundation for uncalibrated runs in the Global Lakes sub-sector.

This entry covers HyLake's contribution to the Local Lakes sub-sector with per-lake calibration on selected well-studied lakes.

Information for the model HyLake is provided for the simulation rounds shown in the tabs below. Click on the appropriate tab to get the information for the simulation round you are interested in.

Person responsible for model simulations in this simulation round
Yuan He: yuanhe@mail.bnu.edu.cn, 0000-0002-2955-1063, Faculty of Geographical Science, Beijing Normal University (China)
Additional persons involved: Xiaofan Yang
Basic information
Model Version: 1.0
Model Homepage: https://doi.org/10.5281/zenodo.15289113
Model License: The Creative Commons Attribution license
Simulation Round Specific Description: For the ISIMIP4b Local Lakes simulations, HyLake v1.0 will be applied to the curated set of well-studied lakes defined in the Lake Sector protocol. The hybrid architecture allows per-lake calibration of the BO-BiLSTM lake surface temperature surrogate using site-specific observations, while the process-based backbone retains physical consistency for surface energy balance and vertical thermal structure. Forcing follows the ISIMIP4b bias-corrected CMIP6 GCM data on a daily timestep. Outputs will include lake surface temperature, vertical thermal structure, and surface latent and sensible heat fluxes, formatted according to the Lake Sector variable definitions. This is the first ISIMIP simulation round in which HyLake is contributed.
Reference Paper: Main Reference: He, Y. and Yang, X. et al. Hybrid Lake Model (HyLake) v1.0: unifying deep learning and physical principles for simulating lake-atmosphere interactions. Geoscientific Model Development,18,9257–9277,2025
Resolution
Spatial aggregation: lake
Horizontal resolution: Site-specific (point)
Vertically resolved: No
Temporal resolution of input data: climate variables: Hourly
Additional temporal resolution information: Climate forcing input is hourly. HyLake's process-based backbone uses an adaptive internal timestep for numerical stability of the vertical thermal structure solver; outputs are aggregated to daily resolution to match the ISIMIP4b protocol. The BO-BiLSTM surface temperature surrogate operates at hourly timestep matching the input frequency.
Spin-up
Was a spin-up performed?: No