Ensemble projections of hydro-biogeochemical fluxes under climate change

• Applicants: Professor Dr. Lutz Breuer; Professor Dr. Jürg Luterbacher
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management ; Atmospheric Science ; Physical Geography
• Term: from 2008 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 65984298

Uncertainty estimation in hydro-biogeochemical modeling is an ongoing area of research that focuses primarily on the investigation of stochastic model uncertainty. The evaluation of structural model uncertainty remains unusual, however there are various techniques available to quantify structural uncertainty. Ensemble modeling is one such technique that is commonly used in climatology and meteorology; disciplines where the structural uncertainty of predictive models has long been established. Its application in hydrological modeling is, however, much less common. Here we propose to evaluate structural uncertainty through *P ensemble modeling, using a set of four models to predict hydrological and nitrogen fluxes: SWAT, LASCAM, HBV-N and CMF-N. The models were selected to represent the range of complexity found in catchment scale modeling, from conceptual models to physically-based approaches, and from lumped to fully distributed descriptions. The GLUE concept is applied to quantify parameter uncertainty. This approach leads to the formulation of single-model ensembles. These single-model ensembles are then combined to produce different sets of probabilistic and deterministic multi-model ensembles. These multi-model ensembles are used to quantify the contribution of structural errors to overall predictive uncertainty. The development of conditional multi-model ensembles represents a large component of the work plan. In this case, the selection of the multi-model ensemble members is based on the capability of different model structures and parameterizations to capture certain conditions of the investigated catchments such as high-low flow, freeze-thaw cycles, or rewetting after extended droughts. The ensemble model is applied to German, Swedish and Australian catchments, and covers a broad range of different climatic boundary conditions, land uses and levels of anthropogenic disturbances.

• DFG Programme: Research Grants
• International Connection: Australia
• Participating Persons: Dr. Jean-Francois Exbrayat; Professor Dr. Douglas Maraun