Coupling a global glacier model with a global hydrological model - benefits, challenges and limitations
Authors: Hanus Sarah , Schuster Lilian , Burek Peter , Maussion Fabien , Seibert Jan , Marzeion Ben , Wada Yoshihide , Viviroli Daniel 
Published: February 2023

Glaciers are present in many large river basins and influence runoff variations considerably in many mountain areas. Due to climate change, annual runoff volumes originating from glaciers and the glacial melt seasonality are undergoing considerable changes. These changes can affect water availability in basins with glacier cover. Nevertheless, glaciers have been largely neglected in large-scale hydrological models so far, which is a crucial limitation in global climate impact studies on water resources.To include glacier runoff in large-scale hydrological studies, we have coupled two open-source and well-documented models: a global glacier model (OGGM, Maussion et al., 2019) and a large-scale hydrological model (CWatM, Burek et al., 2020). The coupling offers an explicit inclusion of glacier runoff in large-scale hydrological modeling, and thanks to the dynamic modelling of glaciers, changes in glacier area and volume are explictly considered.The coupling has been evaluated for selected large river basins, namely the Rhine, Rhone, Fraser and Gloma basins on 5arcmin resolution (~9km) and globally on 30arcmin (~50km) resolution, and differences in simulation results with and without coupling have been assessed. Simulations were run for the recent past (1990&#8211;2019) and for two scenarios (SSP1-2.6, SSP5-8.5) for the 21st century.Including glaciers explicitly in climate impact modelling of large river basins simulates larger future changes in summer discharge. Therefore, it is especially important to include glaciers in studies focusing on changes in summer water availability and its impacts. For the recent past, the contribution of glaciers to discharge at downstream stations of the selected river basins ranges from 7 to 37% for one month and between 2 and 8% annually. For the period 2070&#8211;2099, the projected contribution of glaciers drastically decreases to 2 to 13% for one month and 0.2 to 1.3% annually even under the low-emission scenario.Issues to tackle during the model coupling include precipitation data correction, different spatial and temporal resolutions in the models, &#160;different snow process representations, and the model calibration.Here, we give an overview of the benefits, challenges and limitations of coupling a global glacier model with a global hydrological model and focus on future discharge projections in large river basins.&#160;ReferencesBurek, P., Satoh, Y., Kahil, T., Tang, T., Greve, P., Smilovic, M., Guillaumot, L., Zhao, F., and Wada, Y.: Development of the Community Water Model (CWatM v1.04) &#8211; a high-resolution hydrological model for global and regional assessment of integrated water resources management, Geosci. Model Dev., 13, 3267&#8211;3298, https://doi.org/10.5194/gmd-13-3267-2020, 2020.Maussion, F., Butenko, A., Champollion, N., Dusch, M., Eis, J., Fourteau, K. et al..: The Open Global Glacier Model (OGGM) v1.1, Geosci. Model Dev., 12, 909&#8211;931, https://doi.org/10.5194/gmd-12-909-2019, 2019.