Evaluating a hydrological modelling tool for integration with climate models across Europe

The growing global population and associated socio-economic development are increasing water demand. At the same time, the overexploitation of water resources, particularly in regions with limited availability, leads to mounting water scarcity that is expected to further intensify under projected climate and socio-economic change. Consequently, assessments of current and future water resources need to account for the coupled effects of climate change, human water management practices, and hydrological processes. Despite the widespread relevance of these interactions, significant gaps remain in our understanding of the interplay between (i) human water management, (ii) local-to-basin-scale hydrology, and (iii) hydroclimatological and atmospheric responses. A major reason for this is that many state-of-the-art Earth system models misrepresent or omit critical processes, such as river routing, sectoral water withdrawals, groundwater pumping, and dam/reservoir operations. These limitations constrain our ability to consistently quantify impacts across scales and disciplines and complicate the evaluation of management interventions and their hydroclimatic feedbacks.

Here, we evaluate the performance and highlight the wide range of applications of Climate-CWatM (C-CWatM), a newly developed flexible modelling tool for simulating water resources management and river routing. C-CWatM uses land-surface model outputs as inputs and provides a coupling interface designed for quick integration with existing climate and Earth system models. We force C-CWatM using raw land-surface outputs obtained from high-resolution regional climate model simulations across the EURO-CORDEX domain. To evaluate its performance, we compare simulated discharge between 1990 and 2010 with observed data from medium-sized European river basins. Our findings indicate reasonable performance, even when using raw, non-bias-corrected, unconstrained climate model output for runoff and other land-surface variables as input. We further evaluate the performance of C-CWatM against dedicated hydrological simulations using the offline hydrological model CWatM, driven by tailored, bias-corrected forcing datasets. The results demonstrate a strong agreement in both spatial and temporal discharge patterns, highlighting the effectiveness of C-CWatM in hydrological and water resources simulation for integration with climate models.

Due to its flexible, open-source, and accessible design, C-CWatM represents a critical step towards fully coupled modelling of climate–water–human interactions. The implementation of a coupled modelling system that includes C-CWatM can close the gap between water management, hydrology, and land–atmosphere interaction, supporting more consistent assessments of future water availability, hydroclimatic extremes, and the associated adaptation strategies.