Paired karst–non-karst modeling reveals hidden sensitivity to climatic persistence

Mediterranean basins are increasingly exposed to sequences of dry and wet years that challenge reliable estimates of water availability and ecosystem resilience^1,2.In karst catchments, strong surface–groundwater coupling and large subsurface storage fundamentally alter how precipitation is partitioned and how long hydrological anomalies persist. Although the physical behavior of karst systems is well known, most hydrological assessments and management-oriented studies still rely on models that do not explicitly represent karst processes. Consequently, it remains unclear how much water-balance estimates and management-relevant fluxes would change if karst dynamics were properly accounted for under persistent climatic extremes.
Here we address this gap using a counterfactual modeling framework that directly compares karst and non-karst realizations of the same basin under identical climate and land-use forcing. Our central research question is how climatic persistence (consecutive dry and wet years) controls precipitation partitioning in a Mediterranean karst basin, and how different those responses would be if the basin behaved as non-karst. We hypothesize that explicit representation of karst processes increases hydrological memory, making multi-year climatic sequences more influential than isolated extreme years and leading to substantially different estimates of key water fluxes.
We applied a physically based, distributed hydrological model to the 4,818 km² Mijares River basin in eastern Spain, a heterogeneous karst system with strong surface–groundwater interaction. The model was forced with meteorological data for 2000–2014 and a land-use map derived from the SIOSE 2014 classification. Using the same forcing and experimental design, we generated a counterfactual non-karst scenario in which karst-specific subsurface processes were suppressed.
At the basin scale, results show that karst-induced subsurface storage and delayed water transfer strongly amplify the impact of climatic persistence. In the karst configuration, sequences of dry or wet years exert a stronger control on the partitioning of precipitation into evapotranspiration, infiltration, runoff, subsurface flow, and percolation than do isolated extreme years. In contrast, the non-karst scenario exhibits weaker hydrological memory, with more immediate and climate-proportional responses. In several flux components, the karst and non-karst simulations diverge not only in magnitude but also in their implied hydrological functioning.
At the land-use class level, forests and shrublands in karst terrain promote infiltration and evapotranspiration with negligible surface runoff, reinforcing delayed subsurface responses during dry periods. Agricultural areas show higher interannual variability, while artificial surfaces generate disproportionate increases in runoff, particularly during persistent wet sequences. These contrasts are markedly attenuated in the non-karst experiment.
Overall, this paired karst–non-karst modeling approach demonstrates that omitting or oversimplifying karst processes can lead to substantial errors in both the magnitude and interpretation of water fluxes under persistent climatic conditions, providing a robust basis for evaluating water-resource decisions in karst regions facing increasing climate variability.
References
1 Rivas-Tabares, D., Tarquis, A. M., Willaarts, B., & De Miguel, Á. (2019). An accurate evaluation of water availability in sub-arid Mediterranean watersheds through SWAT: Cega-Eresma-Adaja. Agricultural Water Management, 212, 211-225.
2 Rivas-Tabares, D. A., Saa-Requejo, A., Martín-Sotoca, J. J., & Tarquis, A. M. (2021). Multiscaling NDVI series analysis of rainfed cereal in Central Spain. Remote Sensing, 13(4), 568.