Flash floods are a major natural hazard in Mediterranean regions, causing significant damage to property, infrastructure, and loss of life. Climate change plays a crucial role in altering rainfall patterns, thereby directly affect flash-flood behavior. Despite extensive research, important gaps remain in understanding flash floods, particularly regarding event-based analyses using high-resolution distributed models capable of capturing flood dynamics in heterogeneous catchments and their response to climate-driven rainfall changes.

This study addresses this gap by investigating flash-flood behavior in the Yarkon–Ayalon catchment, a large (1,800 km²) Mediterranean basin in central Israel characterized by pronounced spatial heterogeneity. The upper part of the catchment is largely dominated by natural land cover on permeable soils, promoting higher infiltration, whereas the lower part is flatter and less permeable due to extensive agricultural and urban development, leading to rapid runoff generation during intense rainfall events. Streamflow observations from 14 hydrometric stations span a wide range of contributing areas (7–953 km²), enabling evaluation of flash-flood response across spatial scales at the intra-basin level.

We employ the Grid-Based Hydrological Distributed Runoff (GB-HYDRA) model, an event-based, high-resolution distributed hydrological model developed to simulate runoff and flash-flood dynamics. Model performance is evaluated using 37 historical flash-flood events, with calibration and independent validation conducted across multiple events and hydrometric stations representing different spatial scales. The model demonstrates moderate overall performance, with Kling–Gupta Efficiency (KGE) values of approximately 0.75 for runoff volume and 0.70 for peak discharge.

As a next step, the calibrated model is applied using high-resolution rainfall simulations derived from the Weather Research & Forecasting (WRF) model under historical and end-of-century climate projections (RCP8.5). The analysis focuses on changes in flash-flood characteristics across spatial scales and dominant land-use types, providing insight into the processes linking changing rainfall patterns to flash-flood response.