Multi-parametric variational data assimilation for hydrological forecasting

• Published in: Advances in water resources 2017-12, Vol.110, p.182-192
• Main Authors: Alvarado-Montero, R., Schwanenberg, D., Krahe, P., Helmke, P., Klein, B.
• Format: Article
• Language: English
• Subjects: Data; Data assimilation; Data collection; Ensemble forecasting; Forecasting; Hydrologic data; Hydrologic forecasting; Hydrologic models; Hydrology; Initial conditions; Lead time; Moving horizon estimation; Multi-parametric modelling; Pools; Remote sensing; Rivers; Stream discharge; Stream flow; Streamflow forecasting; Uncertainty; Variational data assimilation; Weather forecasting
• ISSN: 0309-1708; 1872-9657
• DOI: 10.1016/j.advwatres.2017.09.026

•A multi-parametric data assimilation using MHE variational approach is proposed.•Parametric distances are maximized using a novel parametric reduction technique.•Several parameter sets are combined to produce probabilistic initialization.•Multi-parametric assimilation is assessed using lead time performance metrics.•Assimilation of streamflow and H-SAF remotely sensed soil moisture and snow data. Ensemble forecasting is increasingly applied in flow forecasting systems to provide users with a better understanding of forecast uncertainty and consequently to take better-informed decisions. A common practice in probabilistic streamflow forecasting is to force deterministic hydrological model with an ensemble of numerical weather predictions. This approach aims at the representation of meteorological uncertainty but neglects uncertainty of the hydrological model as well as its initial conditions. Complementary approaches use probabilistic data assimilation techniques to receive a variety of initial states or represent model uncertainty by model pools instead of single deterministic models. This paper introduces a novel approach that extends a variational data assimilation based on Moving Horizon Estimation to enable the assimilation of observations into multi-parametric model pools. It results in a probabilistic estimate of initial model states that takes into account the parametric model uncertainty in the data assimilation. The assimilation technique is applied to the uppermost area of River Main in Germany. We use different parametric pools, each of them with five parameter sets, to assimilate streamflow data, as well as remotely sensed data from the H-SAF project. We assess the impact of the assimilation in the lead time performance of perfect forecasts (i.e. observed data as forcing variables) as well as deterministic and probabilistic forecasts from ECMWF. The multi-parametric assimilation shows an improvement of up to 23% for CRPS performance and approximately 20% in Brier Skill Scores with respect to the deterministic approach. It also improves the skill of the forecast in terms of rank histogram and produces a narrower ensemble spread.