Global streamflow modelling using process-informed machine learning

We present a novel hybrid framework that incorporates information from the process-based global hydrological model (GHM) PCR-GLOBWB, to reduce prediction errors in streamflow simulations. In addition to catchment attributes and meteorological data, our methodology employs simulated streamflow and state variables from PCR-GLOBWB as predictors of observed river discharge. These outputs are used in a random forest, trained on a global database of streamflow measurements, to improve estimates of simulated river discharge across the globe. PCR-GLOBWB was run for the years 1979-2019 at 30 arcmin and its inputs and outputs were upscaled from daily to monthly time steps. A single random forest model was trained with these state variables, meteorological data and catchment attributes, as predictors of observed streamflow from 2,286 stations worldwide. Model performance was evaluated using Kling-Gupta efficiency (KGE). Results based on cross-validation show that the model is capable of discerning between a variety of hydroclimatic conditions and river flow dynamics, improving KGE of PCR-GLOBWB simulations at more than 80% of testing locations and increasing median KGE from -0.02 in uncalibrated runs to 0.52 after post-processing. Performance boosts are usually independent of the availability of streamflow data, making our method a potential candidate in addressing prediction in poorly gauged and ungauged basins.

Automated summary

We propose a new hybrid framework that incorporates information from the PCR-GLOBWB model to improve streamflow simulations. By using simulated streamflow and state variables as predictors, along with catchment attributes and meteorological data, the random forest model can enhance estimates of river discharge worldwide. The model shows significant improvement in performance, even in poorly gauged and ungauged basins.