Process-based water balance modelling with explicit ice flow dynamics: WaSiM-OGGM coupling scheme

The water balance in high-alpine glacierized regions is greatly affected by low temperatures and high precipitation. While snow accumulates during winter, maximum runoff driven by snowmelt is observed during spring or summer. Since glaciers act as huge water reservoirs, they might alter the hydrological response of the catchment across time scales, thus affecting the regional water supply or hydropower generation at the regional scale.
The Water Flow and Balance Simulation Model (WaSiM) is a deterministic, process-based hydrological model that allows to describe the hydrological response of a catchment including the variability of glacier areas. In this context, an empirical volume-area scaling approach can be internally implemented to describe the glacier’s evolution. Although acceptable estimates can be obtained with this integrated approach, a representation of the explicit ice thickness is still missing. For this reason, a coupling scheme between WaSiM and a more sophisticated glacier model that accounts for glacier geometry including explicit ice dynamics is developed. More specifically, the Open Global Glacier Model (OGGM), which is an open source modelling framework able to simulate almost any glacier in the world, is used.
The coupling strategy consists mainly on three steps: i) a static model run of WaSiM (daily resolution) to obtain monthly values of temperature and precipitation that serve as input for the ii) second step, which is running OGGM. Finally, iii) a dynamic model run of WaSiM with the updated output from OGGM (i.e. annual glacier mass-balances) is performed. In this last step, the hydrological response of the catchment can be evaluated (for example, through total runoff). The coupled model is calibrated during the 3rd step, thus only WaSiM parameters are adjusted. In this way, no additional expertise on glacier modelling is required from the user, since OGGM is set up according to its default parameters. 
Finally, this coupling scheme could serve as a tool to predict the hydrological response of any glacierized catchment under different climate projections in the future.