In a study recently published in the journal Nature Water, the Technical University of Crete, in collaboration with an international team led by the University of Potsdam, applied for the first time a new method for assessing the consistency of global hydrological models against observations.
Hydrological models applied on a global scale are key tools for the simulation and understanding of the hydrological cycle. Probably the most important use of these models at present is to understand the impacts of climate change. Our society is experiencing many of these impacts through changes in hydrological extremes, such as increased drought and flooding, which are increasing threats to people and ecosystems. But there are also changes in general water availability, for example in soil moisture, which is important for agriculture, or in groundwater recharge, which is important for sustainable groundwater use.
However, inconsistencies between the results of different global hydrological models make these model-based conclusions uncertain. These inconsistencies have not yet been adequately quantified and existing assessment approaches provide limited information on how models could be improved.
This new study is the first to use large-scale correlations between climate and hydrological variables to reveal differences between models and observations. In particular, the correlations between climate and hydrological variables - so-called functional relationships - provide an overview of how the global hydrological cycle works. How much does groundwater recharge depend on rainfall and how strong is the influence of other factors, such as geology? The answers to these questions are extremely important but are often not available for large areas of the land surface, which is reflected in inconsistencies between models.
Associate Professor A. Koutroulis and Dr. M. Grillakis from the Technical University of Crete, contributed to the simulation of the global hydrological cycle using an open-source model developed for the simulation of land surface processes at both global and local scales.
The researchers note that they are looking for new methods to evaluate these highly important models, both to inform decision-makers about the reliability of the models' results and to help improve them further. This offers the potential for fundamental advances in global hydrology and can be a focal point for hydrological research, in particular for model evaluation.
Gnann, S., Reinecke, R., Stein, L., Wada, Y., Thiery, W., Müller Schmied, H., Satoh, Y., Pokhrel, Y., Ostberg, S., Koutroulis, A., Hanasaki, N., Grillakis, M., Gosling, S.N., Burek, P., Bierkens, M.F.P., Wagener, T. (2023). Functional relationships reveal differences in the water cycle representation of global water models. Nature Water DOI: 10.1038/s44221-023-00160-y
